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Any. Good afternoon, ladies and gentlemen, and welcome to the Wilson lecture.

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The lecture is being given in memory of Felix Alexander Lindemann first discount towel.

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He became a doctor. He's professor of experimental philosophy in 1919 and director of the Clarendon Laboratory.

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He was one of the principal scientific adviser to the British government and in particular to Winston Churchill,

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and he brought many fine scientists from Germany in times that were very hard for them to Oxford,

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including Francis Simon, who was also being remembered in the lecture.

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Simon graduated in Berlin in the research group of Bostonians, the low temperature physics,

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unsurprisingly, and he was invited by Lindemann to join the Clarendon in 1933.

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In 1936, he became leader in thermodynamics. And then he joined the Manhattan Project that stayed in the states for a long time.

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He came back to Oxford, and he took place as a police professor in nineteen fifty six.

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Sadly, only one month before he died. This busy slide shows all the lectures in the first 50 years,

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the lectures being held continuously since 1960, with one exception, which I will mention.

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As you can recognise in this slide, most of the goal of late 20th century physics, including many, many Nobel prises.

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Since 2010, we had eight lecturers we most recent ones, including our first female lecturer.

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These are unveiled in 2016 and maybe set three of them Nobel prise recipients.

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You can see we had nine years since 2010 and all the eight lectures and the missing person is.

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Peter Higgs was supposed to have delivered the lecture in 2014, but he had to cancel the last minute.

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Nevertheless, this is the 60th anniversary I will sign the memorialise the very important anniversary and these occasion,

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these occasion is appropriate. It would be appropriate to take, as Jonathan Freedland would say, the long view.

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Sadly, I don't have the time to discuss where physics is coming from and where it's going.

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But I want to take two minutes of your time to discuss a very small pixel of a snapshot taken with a very long lines.

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The physicists in the Western world like to trace back the origin of their subject to a group of early Greek thinkers before Socrates,

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the so-called Pisa products and in particular to the earliest of them hailing

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in the 6th century B.C. from relators known not by chance as the physicist.

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So I ask myself, what would people like sailors or NASA managers on maximalists think of physics today where they if they were alive today,

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would they recognise any of it? I believe they would actually struggle with one important element of contemporary physics, which is the technology,

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in spite of the fact that technology comes from the Greek word TechNet,

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which means that is what is created and taken on, which means creatures including offspring.

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And this is the sense in which Homo uses the world.

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They would struggle because of their aristocratic disdain for anything that had remotely a practical application.

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In fact, the great epic of Hellenistic technology had to wait for another two centuries after Alexander the Great.

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However, the other aspects of physics that I believe they would recognise after all, their quest as their quest is,

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was to explain the cosmos in terms of its own inherent principle without making reference to the Olympian gods.

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And also, they wanted to find what is in common between things that appear very different.

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They believe, for example, that's all things have had something in common conceptually,

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and they call this common concept the archaic the original principle.

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And they would have no difficulty to identify the Ark, their ark with their own theory of everything.

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They also believe that everything that exists in the cosmos has emitted the material principle in common,

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which they call this story came from which the elements, the constituent elements from which are words like geometry.

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They thought this element, the original element, would be something rather simple, like water, fire, earth or air.

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So they will be surprised and amazed to learn of our belief that the principal constituents of

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the cosmos is something not only thoroughly unfamiliar but so elusive to be almost undetectable.

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Yet we know today that indeed, the greatest consumed constituents of matter in the universe is dark matter,

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which would be totally invisible if not for the influence it exerts by mutational differences observed on ordinary matter.

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Today's lecture has devoted the latest part of her career to make the invisible visible.

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And I thought, I give you there for the 60th anniversary lecture, Professor Eleanor a freedom.

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Professor Freeman was born in Milan, my hometown. Alma mater is University of Naples to it to remain in my theme, Napoli's The New City of the Greeks,

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which was built near the site where the siren Pacino, according to legend, drowned herself for the love of Odysseus.

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You get closer to a time, closer to a time.

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She started her research in Geneva with Professor Carla Rubio on liquid imaging detectors.

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And then she continues that at Harvard, as a postdoc at Columbia,

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she pioneered the development of content of its contents, the telescope based on a liquid xenon time projection chamber.

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And then on the basis of that, she proposed this so-called xenon project, which is for direct detection of dark matter using this technology.

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She started the Xenon Dark Matter collaboration in 2002, and she's been the spokesperson ever since.

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She leads a vast team of 170 plus scientists of many nationalities, and she holds countless grants of several millions.

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She had many awards in her career. She became a fellow of the American Physical Society in 2000.

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In 2005, she received a title of Charlie de la Repubblica Italiana from the president of the Republic of Italy, Khalid to Jumpy.

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In 2017, she received an honorary degree from the University of Stockholm.

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She's the recipient of the 2019 AAA Lancelot Purply prise.

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Without further ado, I give you Professor Elena Breguet.

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So it is a pleasure, thank you, Paula, thank you, young, thank you,

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this wonderful physics department and great university for the opportunity to be here.

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It's really an honour and a pleasure to tell you about the xenon project and its search for dark matter.

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And so we go straight there. He already told you that I would like to turn the invisible into visible.

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I wish my dream is actually to contribute to understand this big question about what this majority of the matter in the universe is made of.

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So and that is the goal of my project, which started, as Paolo said quite a few years ago.

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We have been searching with a family of detectors this time projection chambers a technology that the greca,

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which I hope the Greeks would appreciate actually, because they are amazing imaging devices.

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And despite all these efforts of all these years,

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we have yet to see a sign of a particle which we believe could make the dark matter of the universe, but we have not given up.

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This is the year of the xenon enten experiment, which I'll tell you briefly at the end.

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So we are building yet another detector, which is even larger and more sensitive.

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Lower background to to continue to search for this document.

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Dark matter is the dominant form of metal in this university, says invisible in the sense that we cannot use the telescopes that we have built so far.

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None of the telescope that we have built so far to to see it or detected it doesn't emit to absorb light.

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We know of its presence only through its gravitational effects on structures, and I will come to that more later.

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An attractive idea which remains with us today and still quite strong,

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is that this dark matter could be a new form of elementary particle yet to be found,

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and therefore we call it this weakly interacting massive particle.

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And the search for this WIMPs has gone on for tens of years now, and despite some setbacks,

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I think there is reason to believe that this is still a very attractive possibility for the dark matter.

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Whatever the dark matter is, the question remains today that is fundamental in this almost obligatory for us to find an answer,

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because how can we just go by this question, which is one of the most outstanding questions in physics, cosmology, astrophysics today?

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If that is so much connected to our own existence, without dark matter,

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there would not be this galaxy, and I had a nice picture of this beautiful galaxy in which we live.

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I mean, we have parts of this Milky Way, but from galaxy to galaxy to the larger scale structure,

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the glue which keeps all this together is what we call dark matter and with dark matter.

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Therefore, there could not be stars or planets, and we will not be here, so we need to find out what it is.

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And that's the purpose of my research and of the xenon project.

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It is a fundamental question. And so this beautiful picture there, as I already mentioned since the nice Paolo brought in the Greeks,

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I mean, it has been throughout the history of humankind.

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We have tried to understand the cosmos and answer the fundamental question What is the universe made of inventing?

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And I've seen this beautiful lab that Ian has across the road.

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I mean, we love to build instruments and invent new technologies.

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And so throughout the ages, we have been looking at not only our galaxy, but the universe at large with a variety of telescope.

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I was so excited to see pieces of the camera, which will go on the LSC for me, the next generation cosmology.

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So we are going to be essential, fundamental and precise to give us an answer on the other component of the universe, which is dark energy.

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I will not talk about it, but was great to see something being built for electricity here, and that's happening actually almost tomorrow.

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Twenty twenty twenty twenty one. So we have built all these telescopes to look at our galaxy and the universe, a large but none of these.

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So we can look.

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I told wavelengths from gamma rays all the way to radio, but none of these are going to give an answer to this question of dark matter.

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I believe, and I guess many of us believe that the the answer to the question of what dark matter is, my more likely might.

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Unlikely, likely come from experiments, maybe on Earth,

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we don't have to go out there experiments such as xenon or next generation, and so before I go on,

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I think it's also worth to say that what we see with these instruments, the visible matter is actually only one percent of the total.

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When we look at the beautiful sky at night, what we see in stars is actually such a tiny,

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tiny fraction is just the tip of the iceberg because the rest,

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the majority is in gas and dust, which fields this galaxy and the spaces between galaxies.

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And as we already said, the majority is dark matter when we say the majority of the matter in the universe is actually 85 percent to be quantitative.

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And these 85 percent, which is in dark matter, is not the number that we gave up lightly.

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This number comes from observations from observation on all astronomical scales.

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It comes from a variety of measurements from cosmology and astrophysics, and we know it very well.

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And as I said, that explains all of this structure, and we know it so well, mostly for the last 10 or more years through precision cosmology.

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We have this beautiful model of precision cosmology.

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And here, thanks to telescopes such as, of course, the blue map now Planck.

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I'm sorry. Planck no w map of Cuba even before.

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So for the last 20 years, actually or so, Precision Cosmology is giving us an exquisite amount of information about the origin,

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the composition and the evolution of this universe. And and from that.

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And of course, this telescope the the the plan.

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Because of course, looking at the cosmic microwave background,

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which is this leftover radiation made three hundred eighty thousand years after the Big Bang.

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So this is one observation from which the precision of the amount of matter or documents in the universe comes and the rest of this.

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The other component dimension itself is dark energy.

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And I also said that the there is there is a huge effort in building this next generation, more precise surveys to answer the question of dark energy.

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And so, for that matter, the story is very short.

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I can stop talking because we know it's there. We know exactly how much there is from all this observation.

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And unfortunately, despite all the efforts today, we don't know what it is.

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So we know of its existence for almost 100 years now.

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So the most, if you like famous or the most direct evidence or convincing evidence of the presence

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of dark matter is through these studies of the galactic rotational velocities.

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So this is like the stars in the galaxy rotate around the centre, just like planets and our own herd rotate around the sun.

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And so the same way that we can infer the mass of the Sun from the speed of the Earth around the Sun,

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we can infer the total mass of the galaxy from measuring the relative rotational velocity,

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which is depicted here in this cartoon velocity and km per second as a function of the distance of each of the stars from the centre.

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And this is what Vera Vera Vera Rubin in the Seventies with collaborator did the study Galaxy after Galaxy and finding this unexpected.

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And I wanted to say about Vera Rubin because we have a nice symposium next month in her honour.

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As you know, she passed away recently. So from these studies of rotational velocity, we we see these unexpected behaviour.

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Rather than seeing this velocity decreasing as expected from Newtonian mechanics,

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we see these velocities staying constant as far as you can measure is far from the centre as you can measure.

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And the only way to explain this behaviour is to invoke that there is about 10 times more mass in something which is not visible than the mass,

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which is visible in stars and gas and so on. So this is consistent with what much, much earlier.

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This gave three key also found by studying not galaxy, but an entire cluster of galaxies, such as the coma cluster.

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We have to invoke a large amount,

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maybe ten times more mass in Envisat to provide the gravitational attraction for these stars to keep rotating at this constant speed.

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But I think what is actually might? When I think of a way to see the presence of dark matter in systems, in astronomical systems,

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I think of gravitational lensing because I think it's very visual the gravitational lensing,

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which is of course expected or predicted by the general theory of relativity, which tells us that a mass bends light.

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So this is here shown, for example, for this bullet cluster,

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this this this collision of two classes of galaxy, which was observed quite a few years back.

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By now in this bullet curves, the measurement is very clear that the red region there is where the the the hot gas,

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the stuff that is visible is concentrated,

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whereas in the blue in the blue regions that you see in the picture is more the visible stuff and also the X.

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The x rays are in the red, in the red colour and the visible and the dark matter pass through each other without being affected.

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So in order to explain this measurements again, you have this from gravitation, from the gravitational lensing of these two clusters,

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you can infer the amount of document this is, for me, the most visual way of representing the presence of dark matter in the universe.

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So the question remains what it is not if there is there.

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I mean, there is dark matter and there is how much the question is what it is and the what, when before we answer what it is,

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we can just summarise briefly what we know about it from this variety of observation, the quantity I mentioned and we know very precisely this number.

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We know it's called at least moving on relativistic in order to allow these structures to form must be neutral.

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Or we would have detected and it's known baryonic.

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We know again from observation, both from CMB and other from nuclear synthesis.

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We know the amount of variance in the universe. And it must be stable in order to be still here today.

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And so when you put all these requirements together and you ask if any of the standard

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model particle which is schematic represented on the right there with the leptons on top,

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I mean the court on top and the leptons and the force carriers.

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When you ask if any of these elementary particles, the standard model could satisfy all these requirements.

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The answer is no. There is no standard model particle, which can be perfect.

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Document particle can then. So we say we are looking for physics beyond the standard model.

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That's why you hear this. We are looking for something else.

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And the leading hypothesis, which I already mentioned, is that this dark matter might be a new elementary particles,

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something which is a relic from the early universe when it was very hot and dense and so capable of producing stuff.

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And so this will be the weakly interacting massive particle as a relic and lets the universe today.

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And that's the inflation here and CMB we mentioned.

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So we're looking for this particle that if it is long lived or stable compared to the age of the universe,

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should just be around today for us to detect. And that's my, of course, hope and dream.

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And the reason the wimp this particle, as to be clear, is only one of the candidates.

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I didn't put a nice light where you have this view of theories or models that our friends can come up with.

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That is that there is a huge range of particle mass and also interaction strength.

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This is shown in a different way than usually we do where on the horizontal axis you have the particle mass in electron

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volts and on the vertical you have actually the the amount of papers that have been written on the specific candidate.

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And so the WIMP has been a very popular one and for very good reason.

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But I want to leave you the message for some of you, we are not familiar that it could be a fuzzy dark matter,

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which is 10 to the minus 20 something electron bolt. There is a theory.

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My colleagues at Columbia, actually, it could be a primordial black hole as I hear we heard last.

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I mean, you heard maybe recently a talk to the big black holes. It could be.

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Clearly, oxygen is a very well-motivated candidate and searches are going on for axial or sterile neutrino.

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But WIMPs have received a lot of attention, a lot of papers.

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And the reason why the WIMP is such a popular candidate, I think, is because it's theoretically like the oxygen is theoretically well motivated.

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We we have extensions of the standard model, such as supersymmetry or extra dimensions.

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Where a wind naturally comes comes out for fixing other problems in particle physics,

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so the neutral line or the least supersymmetric particle in Susi would be an ideal wind.

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And so we're still hoping to get this that I see with it, with the next generation, I mean, the upgrade.

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So we feel searching for new physics, the accelerator and we also still dreaming to find this particle in a direct detector,

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you know, direct detection experiment.

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So if they're there these particles, then we can calculate from the amount of dark matter that I know from astrophysics and cosmology, from CMB.

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I know how much dark matter there is in the halo of this galaxy and we know something about their velocity distribution.

197
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We know, and most recently, we have this Gaia measurements coming up with shaking a bit to the field,

198
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but we can calculate how many of them are around today.

199
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And so actually, you can put down the numbers and you know, very well, it's we have a large amount of particles going through you and me every second,

200
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but only a handful of them care to do any interaction with me or you or with our body, which anyway are not very good detectors.

201
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So we are searching for a very rare interaction and we are looking in three different ways before I move on to my specific topic.

202
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We have been looking for these WIMPs in three direction.

203
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I mentioned already accelerators such as at the Large Hadron Collider with Atlas and CMS and other detector,

204
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mostly Atlas and CMS, with searching for production.

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I mean, for new particles,

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we are also searching for the standard model particles the the UN relation products so wimps in dense regions of the cosmos,

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such as in the Sun or the centre of this galaxy, looking for gamma rays?

208
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We have Fermi satellite out there. We're looking for neutrinos. With IceCube, we're looking for aren't a particle, let's say.

209
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With the mass spectrometer, indirect detection is another area of search for WIMPs.

210
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And then we have the direct detection area where essentially is very simple there way we rely on this seminal paper that

211
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was written already a long time ago now by Goodman and Witten about the detectability of a certain dark matter candidates.

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And the principle is very simple.

213
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They suggested that if this particle is there, we can simply measure the energy which is transferred when a wimp scatters off an atomic nucleus.

214
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So is an elastic scattering of this particle, which could be v scale hundreds of GeV, hopefully a TV scale.

215
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And as a wimp scatters off a nucleus of an atom of standard matter, it will transfer some of these energy to this nucleus.

216
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This nucleus records and the energy of the recoil is our observable.

217
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And so that is the the first challenge that this and experimentalists looking for to build a direct detection experiment.

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The first question you want to probe is how much energy do I need to detect what is the best detector?

219
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And you can calculate from kinematics how much energy for different targets.

220
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And we're always talking about key. The scale tends to give very low energy, which is not typical of your standard gamma rays in the lab.

221
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So first challenge is the very low energy that you need to detect if a wimp scatters off a nucleus of an atom.

222
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And the next question that you ever see in experimentalists will be the next question I ask would be, but how many particles do?

223
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What is the rate? How many events do I suspect for unit time, unit mass units, energy the rate.

224
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And you can imagine that the rate of interaction of these WIMPs with matter depends on the number of particles in the halo of the Milky Way,

225
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where we are, it depends on their velocity distribution. You need to integrate over the velocity distribution.

226
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It depends on the mass of the how many nuclei I have in my target, but also in the mass of the WIMP and the cross section,

227
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which would come from some supersymmetric model, for instance, or some theoretical model.

228
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So when you put it together on this plot, here, I have the calculation of the rate assuming one cross-section,

229
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which is 10 to the minus 46 square centimetre here for the spin independent cross sectional when.

230
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With my just taking a number, which is the level where we are today, as I, we'll get to later and they assume assuming that this wimp is 50 GB mass.

231
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If you take this assumption for the US, if you like from the theory and you calculate for Zenani Germanium and argon,

232
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three of the target elements which are being used in these detectors with different as you see atomic number,

233
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what you want to take away and the rate here in events per K.V. per ton of

234
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material per year is shown as a function of the energy of the recoiling nucleus.

235
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The one the observable that I need to measure and what you want to take away is that if my detector,

236
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let's say the red curve is for Xena, which is the largest of these three nuclei here,

237
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if I can see 10 K view of energy with my detector and I have such a cross-section from some theoretical model,

238
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I only can see 15 events per person per 10000 kg of stuff per year.

239
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So I need to be very patient because I need to put together 1000 kg of Xena target within a year to see 15 events, assuming that this is correct.

240
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So we are talking. The second challenge of this direct detection is, of course,

241
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this very low rate and the low rate would not would not be as challenging if you compare it to the huge rate of other events, background events.

242
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So we have to face and to me, that's the holy grail of research search as we know you would not win by not reducing the

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background or the noise of your detector of your experiment to unprecedented low levels.

244
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So the third challenge is really to control and reduce the background.

245
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I put that cartoon wherever I took this from I and remember Trinity College.

246
00:29:18,070 --> 00:29:22,030
But that's I mean, that's more for a public lecture was to say that.

247
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I mean, we are radioactive. Yeah, definitely. I'm very radioactive, especially when when I talk about ways, the Geiger counter.

248
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But we have a lot of radioactivity naturally in radioactivity, in materials with which we build detectors.

249
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Intrinsic L.A. It is one source, but there are other sources of Beckman that we have to fight,

250
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and we have been getting better and better in the last 10 years, I would say.

251
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In both finding the lowest radioactivity material to build these experiments, sometimes you have contradictory requirements,

252
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you have to do cooling and you have to build also something which is less hot and also trivial as a bigger.

253
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But we also, as you know, control other sources of background,

254
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which I maybe summarise a bit here in the sense that the the reason why all these experiments are actually operated,

255
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not in this lab, on my lab at Columbia,

256
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but deep in a mine or in a in an underground tunnel, is because the first thing we want to do is to shield ourselves from cosmic radiation,

257
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cosmic ray muons that are attenuated by that and the enemy the cosmic ray muons bring us are the neutrons.

258
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So neutrons are the worst enemy for a dark matter search since the neutral and neutron behave exactly like a wimp gives similar signature,

259
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with the exception of the multiplicity of interaction, which you can take advantage of if you build a large experiment,

260
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I'll come to that later so we go deep underground to attenuate the flux of cosmic radiation.

261
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We choose these materials to have the lowest gamma beta radioactivity by painful searches,

262
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namely screening, where every piece of plastic or metal that we use,

263
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we don't just buy then build, but we just undergo a very serious screening campaign to select the most appropriate.

264
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And that can take months and essentially also very good dealing with manufacture because no

265
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steel product producer wants to keep 10 plates of metal for you until you finish your counting.

266
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And so usually I have to intervene and I've managed so far,

267
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but it is a very hard challenge to identify the lowest activity material to build your detector.

268
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And ultimately, you have, of course, this other radiation neutrinos, which will become finally our signal.

269
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So neutrinos from the sun neutrinos melt atmospheric neutrino from supernova.

270
00:32:05,920 --> 00:32:11,770
Hopefully, these detectors that we are building as we scale up in sensitivity are going to become

271
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neutrino detectors because we have no way of distinguishing then the signal from neutrinos,

272
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from the signal, from a wimp. And so these are the challenges, the energy.

273
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Extremely challenging, low energy, the very low rate compared to these huge background, and of course, the new train also called the floor,

274
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as we call it, there is a certain limit after which we're going to actually searching for neutrinos because we will not distinguish this wimp from it.

275
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So now we have been very inventive in choosing targets and techniques and experiments.

276
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This is just a zoo of the many experiments and techniques that people have used and are still using today to search for dark matter.

277
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And so we go from bubble. Beautiful bubble chambers to scintillating to ioniser.

278
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And essentially the principle is that whenever you have radiation such as that from a recoiling nucleus hit by by a wimp,

279
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when you have radiation in a material, you're going to have other ionisation, scintillation or vibration of the letters.

280
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So a variety of experiments many of them use, actually two of the signals are the charge a or charge and phone on.

281
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Very few use just one signal because, as we mentioned,

282
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the holy grail is to have a handle on the background and the more information you have, the better you are.

283
00:33:42,670 --> 00:33:45,460
So I'm going to, of course,

284
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not give you much information about all these experiments that you see is quite a variety in the variety of technology and targets.

285
00:33:53,980 --> 00:34:02,680
But when you look at what the state of the Earth is, there is a plot that I can show and namely that the field, of course, is very competitive.

286
00:34:02,680 --> 00:34:09,310
We are searching for something which is definitely, I still believe, worthwhile searching.

287
00:34:09,310 --> 00:34:13,330
And so there's a lot of competition, but the progress has been very rapid.

288
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This is as a function of time.

289
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The cross section that has been, let's say, probed the cross section for coherence, scattering a wimp on nuclear arms in square centimetre.

290
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So that's the cruise section as a function of time.

291
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And you see, I think what's relevant, we haven't seen a signal, but what we have done in the last 10,

292
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15 years is to exclude or probe four or five orders of magnitude in this cross section.

293
00:34:41,890 --> 00:34:45,370
And what I and of course,

294
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the red triangles are the leading edge technology which has been able to achieve the the

295
00:34:51,580 --> 00:34:57,160
fastest progress and the best progress has been the liquids in detective technology.

296
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Those are the triangles and that gives you an idea.

297
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And also, we have gone from 10 to the minus 40 or so square centimetre to two better than 10 to minus 46.

298
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So this is in the last 10, 15 years or so and incredible progress.

299
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And I hope that in the next five years, in case I missed two, if not in my conclusion,

300
00:35:23,890 --> 00:35:29,620
but of course, we are looking forward to the next decade and the next four or five years.

301
00:35:29,620 --> 00:35:37,420
We'll see another order of magnitude improvement. And and you might say, and what if you don't find it yet?

302
00:35:37,420 --> 00:35:40,630
And so the point is that at this stage, especially in my life,

303
00:35:40,630 --> 00:35:48,520
I never felt better off finding nothing because even if we find nothing is going to be really a paradigm shift because we have,

304
00:35:48,520 --> 00:35:50,620
we would have put to rest completely.

305
00:35:50,620 --> 00:36:01,720
This idea that dark matter is, let's say, a weekly interacting, massive particle and kind of direct our both experimentally and theoretically,

306
00:36:01,720 --> 00:36:10,780
the field in searching elsewhere is going to be very important to finally explore the whole parameter space as sometime we say,

307
00:36:10,780 --> 00:36:17,290
with the next generation of experiments such as the one we're building, we're getting very close to that.

308
00:36:17,290 --> 00:36:22,180
Of course, theorists will still give us some solutions.

309
00:36:22,180 --> 00:36:31,390
But in terms of the wimp particle, I think we're getting very close to where the findings or finally put it to rest.

310
00:36:31,390 --> 00:36:35,500
Now you can see it in these other plants. I mean, this is the standard.

311
00:36:35,500 --> 00:36:39,710
Where is it? Sorry, there was an error and the little.

312
00:36:39,710 --> 00:36:48,770
Person, I found usually you see more like this in talk, that's the state of the art of direct detection with a variety of experiments,

313
00:36:48,770 --> 00:36:54,590
not all of them are shown again cross-section versus the mass of the wimp.

314
00:36:54,590 --> 00:37:02,990
And you can see all the solid lines are exclusion limit constraints, which have been placed by a variety of experiment.

315
00:37:02,990 --> 00:37:11,540
And the dotted line are what are projection on what experiments are going to do in the next, let's say, four or five years.

316
00:37:11,540 --> 00:37:18,680
And so you see that we are going the best current constrained or limit is the solid black line,

317
00:37:18,680 --> 00:37:22,970
which was placed last year by the xenon one time experiment with a few times,

318
00:37:22,970 --> 00:37:33,560
then with minus 46 square centimetre for a 30 or so GeV wimp and the next generation xenon in tone and Elzie,

319
00:37:33,560 --> 00:37:38,960
similar of similar sensitivity, are going to probe an order of magnitude.

320
00:37:38,960 --> 00:37:46,100
And ultimately, we are speaking of a next generation yet observatory, the Darwin Observatory,

321
00:37:46,100 --> 00:37:53,210
which will finally explore the entire region for heavy winds down to the neutrino floor.

322
00:37:53,210 --> 00:37:59,030
So that's what we are looking for forward to in the next decade or so.

323
00:37:59,030 --> 00:38:05,600
But again, it tells you that Xenon has been leading the search, and the reason is why xenon.

324
00:38:05,600 --> 00:38:12,980
I mean, just a few words about what is special about this zone and I took the periodic table is a noble gas on the right.

325
00:38:12,980 --> 00:38:16,280
And so I like to speak for an hour about my favourite liquid.

326
00:38:16,280 --> 00:38:22,250
But anyway, it's one of the noble gases is not the heaviest is the heaviest, actually, if you exclude radon,

327
00:38:22,250 --> 00:38:29,930
which is radioactive anyway, and so it is abstracted from the atmosphere is a by-product of air distillation,

328
00:38:29,930 --> 00:38:43,340
and it's actually their distillation is driven by the need of oxygen, which is needed to to produce steel and therefore the price of the zone.

329
00:38:43,340 --> 00:38:53,810
And we chase in the atmosphere one of the rarest in terms of per mole point or nine, uh,

330
00:38:53,810 --> 00:38:59,570
10 to the minus maybe parts per billion, I forgot the very, very tiny amount in the atmosphere.

331
00:38:59,570 --> 00:39:08,360
So the price of this xenon gas, which is extracted from the air, is actually fluctuating with the economy because it is a by-product of oxygen.

332
00:39:08,360 --> 00:39:16,910
So if we need to build a lot of new building like this once or bridges, we need steel and we need oxygen.

333
00:39:16,910 --> 00:39:22,130
And so the prices is low. Otherwise the price of when the economy slows, it just shoots up.

334
00:39:22,130 --> 00:39:27,980
So even if it shoots up, actually, these are the last bullet is the moderate cause.

335
00:39:27,980 --> 00:39:32,780
Why xenon is interesting for dark matter, specifically document to target or detect it is there.

336
00:39:32,780 --> 00:39:43,570
Despite this fluctuation with the market, you actually have a very modestly cost of material compared to semiconductor or other.

337
00:39:43,570 --> 00:39:50,760
The target, let's say, even $2000 per kilogram today compared to I don't know why I put gold because I like gold,

338
00:39:50,760 --> 00:39:55,910
but I mean, it's still cheap, but it's very cheap compared to germanium or silica.

339
00:39:55,910 --> 00:40:04,190
So you can have the first driver for the noble liquid, such as xenon was the scalability of this dark metal detector,

340
00:40:04,190 --> 00:40:13,070
and we have been able to put together more than 3000 kilogram detector starting from a twenty five kilogram detector has been a huge progress,

341
00:40:13,070 --> 00:40:18,500
not just in terms of four or five orders of magnitude exclusion of these WIMPs,

342
00:40:18,500 --> 00:40:27,390
but we have also improved the technology and build detectors which have gone from tens of kilograms scale to thousands of kilograms with xenon,

343
00:40:27,390 --> 00:40:32,180
one town being the first t.p.s. with three thousand three hundred kg,

344
00:40:32,180 --> 00:40:37,850
and now we're building an eight thousand four and a kilogram detector, which seems actually unreal.

345
00:40:37,850 --> 00:40:46,280
But the reason why we like it. First of all, for wind, for coherence gathering of these particles, nucleon is a very large nucleus.

346
00:40:46,280 --> 00:40:49,730
So there's a lot of protons and neutrons to scatter.

347
00:40:49,730 --> 00:40:58,970
Officer is good for spin independent coupling, but xenon also has a variety of isotopes with spin, and so we can probe simultaneously.

348
00:40:58,970 --> 00:41:06,950
If this wimp likes the spin and maybe does something with this nucleon so we can improve spin dependent coupling with the same target,

349
00:41:06,950 --> 00:41:15,050
which cannot be said for our goal. For instance, the cryogenics, I think that's been as been a showstopper for a long time,

350
00:41:15,050 --> 00:41:19,820
but we don't use xenon from the endless field as a gas we use.

351
00:41:19,820 --> 00:41:24,230
Oh, I see. I'm sorry. It's too active.

352
00:41:24,230 --> 00:41:29,690
We use xenon in its liquid form, so we take the gas, we condense it.

353
00:41:29,690 --> 00:41:33,020
We go to freeze painful process of making it liquid.

354
00:41:33,020 --> 00:41:39,380
And the reason is that in the liquid state it is three grams of super CCS is a very dense liquid with a.

355
00:41:39,380 --> 00:41:45,470
Fifty 54, it gives you a very good stopping material for penetrating radiation,

356
00:41:45,470 --> 00:41:52,380
you need only the mean free path of enemy v gamma ray in liquid xenon is five and a half or so centimetres,

357
00:41:52,380 --> 00:41:56,870
so only a few centimetres of Xena can absorb a lot of these radioactivity,

358
00:41:56,870 --> 00:42:03,050
let's say from wolves of the container, from the photo sensors and so on, a very good stopping material.

359
00:42:03,050 --> 00:42:07,940
And we have learnt how to make it liquid with commercial technology.

360
00:42:07,940 --> 00:42:13,820
We have a mature technology today with cryo coolers, Paul's tube refrigerators in particular,

361
00:42:13,820 --> 00:42:17,900
which we have shown to not only liquefy but also maintaining cold.

362
00:42:17,900 --> 00:42:24,200
This liquid masses of liquid at the tone scale over periods of a year or more.

363
00:42:24,200 --> 00:42:31,460
And as you can imagine, for the next generation, we need to operate this detector, not flame for a year, for more than a year.

364
00:42:31,460 --> 00:42:36,650
We need three or four years of running in order to acquire the statistics that we need.

365
00:42:36,650 --> 00:42:44,330
So stability of the detectives are essential and so mature technologies are needed.

366
00:42:44,330 --> 00:42:54,710
I think the most important of the no intrinsic radioactivity is also important only Krypton, which is also a noble gas.

367
00:42:54,710 --> 00:42:55,310
And you, of course,

368
00:42:55,310 --> 00:43:04,280
when you strike from the area of all kinds of stuff with Krypton is a war is a worrisome contaminant because of the Krypton 85 radioactive isotope.

369
00:43:04,280 --> 00:43:10,970
But we have mastered out to reduce the amount of Kryptonian xenon again by cryogenic distillation.

370
00:43:10,970 --> 00:43:16,310
To me, the most important reason why we use xenon is because amongst all the normal liquid,

371
00:43:16,310 --> 00:43:20,780
it is the best ionised and sincerely to namely the light field.

372
00:43:20,780 --> 00:43:31,400
How many photons per unit energy the charge yield, how many carriers you have is the highest compared to argon, let's say, or others mostly are.

373
00:43:31,400 --> 00:43:39,740
And so the the two signals of ionisation and scintillation which are producing liquid Xena through this complex mechanism.

374
00:43:39,740 --> 00:43:42,920
But most in simple words, whenever you have radiation,

375
00:43:42,920 --> 00:43:49,550
you're going to have other direct excitation of xenon atoms and molecules and you produce these estimates,

376
00:43:49,550 --> 00:43:55,400
which then go to the ground state by this photon scintillation light photons,

377
00:43:55,400 --> 00:44:05,810
which find the very deep you 178 nanometre direct scintillation like the scintillation light is actually prompt few nanoseconds fast.

378
00:44:05,810 --> 00:44:15,560
And it's also very much the decay component depends also on the particle, so you can have particle identification from the pulse shape of the light.

379
00:44:15,560 --> 00:44:21,620
You, you, you contribute to the light. So call this one signal in our business.

380
00:44:21,620 --> 00:44:26,600
Direct light is also produced from the recombination process, which is field dependent.

381
00:44:26,600 --> 00:44:36,530
However, the electron ion pairs produce in liquid xenon by ionisation like to recombine each other unless you apply an electric field.

382
00:44:36,530 --> 00:44:42,020
We do apply an electric field, but a certain fraction of an electron recombine,

383
00:44:42,020 --> 00:44:47,240
and the recombination process also leads to the formation of the same excitement and to light.

384
00:44:47,240 --> 00:44:55,160
So we have to origins of this in the laser light and liquid xenon, and we use both and the Oregon particle dependent.

385
00:44:55,160 --> 00:44:59,270
And then you have the ionisation signal, the charge, which we call us to.

386
00:44:59,270 --> 00:45:06,770
We don't detect the majority of the energy which has actually goes inelastic nucleus scattering the heat.

387
00:45:06,770 --> 00:45:16,100
Not yet in this detector. So we take advantage of both signatures of light and charged produced by radiation only cuisine.

388
00:45:16,100 --> 00:45:22,460
Having solve the technical challenge of detecting 178 nanometre light working

389
00:45:22,460 --> 00:45:27,230
with manufacturers such as armaments over more than 10 years to build tube,

390
00:45:27,230 --> 00:45:36,830
which can not only have decent efficiency of these very deep UV light, but also the challenges that they have to work and minus under the greasier.

391
00:45:36,830 --> 00:45:39,530
So I forgot to mention we liquefy Xena.

392
00:45:39,530 --> 00:45:46,490
The easy cryogenic means close to minus under the greasy, which still very warm compared to nitrogen or Oregon temperature.

393
00:45:46,490 --> 00:45:51,380
But this fortitude working on minus under is not something you buy off the shelf.

394
00:45:51,380 --> 00:45:59,510
And the other challenge you tell Amazon despite all the money you want the least uranium, thorium and potassium and all the rest.

395
00:45:59,510 --> 00:46:05,330
So they're reducing the radioactivity of the entire envelope of all the diner's structure.

396
00:46:05,330 --> 00:46:12,410
Everything which makes a PMTA has been a saga which we have worked together with the manufacturer.

397
00:46:12,410 --> 00:46:20,150
So quite few challenge to have photo sensors to see this light, and we have actually solved the problem, at least for liquid.

398
00:46:20,150 --> 00:46:27,980
So we take advantage of these two signals in a time projection chamber and a time projection chamber.

399
00:46:27,980 --> 00:46:39,210
Essentially, the 3D imaging device is in homogeneous detector, where you have this volume filled with purified liquids RNA and you are.

400
00:46:39,210 --> 00:46:44,820
An electric field across electrodes to produce, of course, to allow the chargers,

401
00:46:44,820 --> 00:46:53,970
which are free from two to separate the electrons from the ions and and and raised the charges against this electric field.

402
00:46:53,970 --> 00:46:58,950
But we are not attempting to directly measure these few electrons, which are produced by a,

403
00:46:58,950 --> 00:47:03,720
let's say, a 10 K the nuclear recoil because this is a slight escape.

404
00:47:03,720 --> 00:47:10,320
But for many years from the beginning of this business, the question I have in mind is not so much if wind exists or not,

405
00:47:10,320 --> 00:47:14,010
but how many electrons and how many Fullerton's is them?

406
00:47:14,010 --> 00:47:24,210
10 KV recall gives me the detector. We had no idea because nobody had measured 10k v nuclear recoil with neutron neutron scattering experiment.

407
00:47:24,210 --> 00:47:27,810
Dedicated experiment. And the story is very simple.

408
00:47:27,810 --> 00:47:40,500
You expect maybe five electrons, per K.V. in terms of if a nuclear recoil or one CV's about five or six electrons or so in the same four photons.

409
00:47:40,500 --> 00:47:46,320
So it means that you are really looking for a handful of photons and the handful of carriers to

410
00:47:46,320 --> 00:47:51,810
detect you're not going to have a charge sensitive amplifier to detect the tiny charge signal.

411
00:47:51,810 --> 00:48:00,360
The trick has been from the beginning, the so-called dual face-to-face time projection chamber essentially that the free electrons,

412
00:48:00,360 --> 00:48:05,730
which are free from electro negative impurity, which make it across the field,

413
00:48:05,730 --> 00:48:14,770
we extract them easily because of the ionisation of funding from the point of view of potential is very easy to extract.

414
00:48:14,770 --> 00:48:23,400
This carries from liquid took us, so we extract them from liquid to the gas phase on top by applying a very strong field in the gas,

415
00:48:23,400 --> 00:48:29,970
and there's the accelerating the gas on top of the liquid. These electrons produce more, more V2V photons,

416
00:48:29,970 --> 00:48:36,360
so we end up we end up changing the charge signal into a light signal and using the

417
00:48:36,360 --> 00:48:41,580
same photo sensors to detect both the primary light and the secondary scintillation,

418
00:48:41,580 --> 00:48:51,360
which is proportional to the energy deposited. So we have so far these experiments I've used to arrays of photo sensors,

419
00:48:51,360 --> 00:48:59,580
one placed in the liquid below the catalyst to see mostly the primary scintillation light because of total internal reflection.

420
00:48:59,580 --> 00:49:04,080
You need a big photo tube down there or very closely packed array.

421
00:49:04,080 --> 00:49:09,180
And then the other array of photo sensor is placed in the cold gas above the liquid.

422
00:49:09,180 --> 00:49:15,540
And from the pattern of light, which you can measure, you can see on your photo sensors.

423
00:49:15,540 --> 00:49:24,810
You actually can reconstruct the X and Y position of the interaction, and the third coordinate comes from the measurement of the drift time.

424
00:49:24,810 --> 00:49:32,940
If you know the drift velocity, you get the Z coordinate so you have a 3D imaging detector, which enables you very powerful.

425
00:49:32,940 --> 00:49:39,840
And the most powerful advantage of these 3D tips is actually to on an event by event basis to

426
00:49:39,840 --> 00:49:45,390
fiducia lies your volume to know where the event happens and therefore choose only a central volume,

427
00:49:45,390 --> 00:49:49,140
which is very free, is depicted here.

428
00:49:49,140 --> 00:49:59,940
You can choose whatever volume is less radioactive if you like, or less free and more free from vehicle to be your target for a whim search,

429
00:49:59,940 --> 00:50:07,680
which has been very powerful in controlling and reducing the background and the wave form that you see on the bottom.

430
00:50:07,680 --> 00:50:17,640
The other advantage that we take of this to signal is that the ratio of the charge to light in liquids in it is very strongly,

431
00:50:17,640 --> 00:50:22,530
very different for a minimum ionising particle than for a neutral wimp.

432
00:50:22,530 --> 00:50:33,190
All the same energy. So this is the additional discrimination parameter that we use that ratio charged to light in the cuisine.

433
00:50:33,190 --> 00:50:37,830
And maybe I forgot something else, but I think is mostly visualisation.

434
00:50:37,830 --> 00:50:43,530
Of course, the stopping power of xenon itself, the edges we can reduce very weak.

435
00:50:43,530 --> 00:50:48,180
We stay away from. If you look at one of the distribution of events in these detectors,

436
00:50:48,180 --> 00:50:56,040
you see all these large rates next to the photo photo sensors next to the walls where the radioactivity,

437
00:50:56,040 --> 00:51:06,120
let's say cobalt 60 or potassium 40 different parties more abundant and you're going to cut out those regions by having this 3D imaging.

438
00:51:06,120 --> 00:51:10,830
So we have made a huge progress over time with this family of detectors,

439
00:51:10,830 --> 00:51:19,320
including some by other collaborations, which will come from the same friends.

440
00:51:19,320 --> 00:51:26,190
We were all together, but then we split. But we what we have done is to actually going from the xenon 10 detector we

441
00:51:26,190 --> 00:51:32,730
take the blue are the number of kilogram in the field as a target for WIMPs.

442
00:51:32,730 --> 00:51:38,580
We have gone from five kg to thousand or thirteen and a kilogram today and.

443
00:51:38,580 --> 00:51:44,910
But we would have not reached anywhere by just scaling up the mass and being able to cool a few

444
00:51:44,910 --> 00:51:51,030
thousand kilograms if we wouldn't have reduced the bottom boxes show the amazing progress we

445
00:51:51,030 --> 00:51:56,640
made in controlling and reducing the backward and where xenon 10 was completely radioactive in

446
00:51:56,640 --> 00:52:01,230
the sense that it was a prototype almost built off the shelf or whatever I had at Columbia,

447
00:52:01,230 --> 00:52:05,550
then to the lowest background detector that we have ever built.

448
00:52:05,550 --> 00:52:17,610
Xenon one thing today is the lowest background we are measuring point two events per ton per K.V. per day in the xenon 110, despite its large size.

449
00:52:17,610 --> 00:52:23,640
So that has been, in my opinion, one of the greatest achievement that we have made with the Zen programme,

450
00:52:23,640 --> 00:52:30,960
which has enabled us to do not only wimp surge, but also other rare events such as I hope I'll have time to tell you.

451
00:52:30,960 --> 00:52:41,400
So implementing the TPC, which I hope I explain to you in this in this phase programme of xenon from xenon 10 to zero one ton,

452
00:52:41,400 --> 00:52:47,190
which by now is stopped, we stopped it at the end of last year to make room to this current phase,

453
00:52:47,190 --> 00:52:54,420
which we call xenon intone with 8400 and the challenge and to achieve another order of magnitude,

454
00:52:54,420 --> 00:53:02,040
both with the scale mass, but also look at the the background reduction or another factor of 10.

455
00:53:02,040 --> 00:53:07,440
But look at the challenge in terms of the technology, we are going to drift from 15 centimetres, you know,

456
00:53:07,440 --> 00:53:16,050
10 to 150 in xenon and time, which has never been done, is, you know, one tonne was the first t.p.s. with a metre drift.

457
00:53:16,050 --> 00:53:21,930
And now we want to go one enough hopefully will work, but that's where we are planning to do.

458
00:53:21,930 --> 00:53:27,870
And and whereas in and of course, xenon, as I mentioned, we are not the Columbia.

459
00:53:27,870 --> 00:53:33,810
We're not in either the rain or we're not here. We are under the beautiful mountain of the central opinion.

460
00:53:33,810 --> 00:53:38,670
We are at the laboratorio nazionale, the Gran Sasso in central Italy.

461
00:53:38,670 --> 00:53:50,190
And so, as you know, L'Engle's is one of the so far is still the largest underground laboratory worldwide is not as deep as others,

462
00:53:50,190 --> 00:53:56,730
such as no lab or the Jingping lab in China, but it is a wonderful place to operate.

463
00:53:56,730 --> 00:54:02,640
These rare event searches and xenon programme has been deployed against us and since the beginning,

464
00:54:02,640 --> 00:54:08,280
with xenon 10s in an underground interferometer tunnel and xenon one tunnelling all be one of

465
00:54:08,280 --> 00:54:17,450
the three big caverns or cathedral that these laboratory offers is about 100 metre long tunnel,

466
00:54:17,450 --> 00:54:22,390
not tunnel covers about what is a 15 metre tall.

467
00:54:22,390 --> 00:54:29,400
So they are beautiful spaces where we actually don't have to back too much.

468
00:54:29,400 --> 00:54:36,960
When you graduate student to go and spend not just a week, maybe months of time because the wine is cheaper than Coke, that's what they tell me.

469
00:54:36,960 --> 00:54:42,030
So but they love to go to lengths and that's where xenon is.

470
00:54:42,030 --> 00:54:49,290
And this this. I wouldn't be doing it without these mostly young guys and maybe the oldest.

471
00:54:49,290 --> 00:54:53,880
So the collaboration is today more than a hundred and seventy people.

472
00:54:53,880 --> 00:54:59,340
This is a collaboration meeting at Columbia actually last May a year ago.

473
00:54:59,340 --> 00:55:03,510
So a lot of post-docs, students, a lot of graduate students.

474
00:55:03,510 --> 00:55:10,620
And the thing? And so of course, they're coming from different U.S. institution University of Chicago Arise,

475
00:55:10,620 --> 00:55:17,850
Purdue and San Diego and whatever, but also all around the world, actually a lot of European, as you know.

476
00:55:17,850 --> 00:55:27,000
But what I'm most proud of actually, is this moving these people around the collaboration and of course, to the competing experiment.

477
00:55:27,000 --> 00:55:33,450
Once you mentally you train these people in the art of this cryogenic noble liquids,

478
00:55:33,450 --> 00:55:37,410
it's a very specialised field and there are very few around the world.

479
00:55:37,410 --> 00:55:44,610
So when they finish the graduate students, we encourage them to get a postdoc here and there and stay within Zen.

480
00:55:44,610 --> 00:55:52,080
And that does work very well. And to the advantage of the project and the fact that these detectors are still

481
00:55:52,080 --> 00:55:58,890
tabletop zen one time and even an almost can be the TPC can be on this table actually

482
00:55:58,890 --> 00:56:03,390
empowers these young people because they can contribute to every aspect from the

483
00:56:03,390 --> 00:56:10,130
beginning they feel really connected in and they feel the maker of the experiment.

484
00:56:10,130 --> 00:56:14,580
So it has been so far an easy task. I don't know with the scale up for that.

485
00:56:14,580 --> 00:56:23,070
But so that's the collaboration, and this is how it looks like if you visit this underground, this is an overview of all of the system.

486
00:56:23,070 --> 00:56:29,400
Zino went on and on and on. We will use the same shielding being underground.

487
00:56:29,400 --> 00:56:36,450
A and sensor with 15 under a metre of rock is still not sufficient to attenuate all the cosmic radiation.

488
00:56:36,450 --> 00:56:38,370
So we use a lot of other.

489
00:56:38,370 --> 00:56:47,880
Of shielding, and of course, as the experiments have increased, the most popular and cost effective materials become water purified water,

490
00:56:47,880 --> 00:56:58,230
which is actually implemented instrumented with photo multipliers so that you turn your water tank, tank or water into a Cherenkov muon detector.

491
00:56:58,230 --> 00:57:08,730
So the Zino went on time projection chamber and the next one is in a seven under cubic metre tank filled with pure water ferrel type.

492
00:57:08,730 --> 00:57:15,270
We have a purification plant, and this water and this water tank is, of course,

493
00:57:15,270 --> 00:57:24,560
lined with photos tube waiting for the multiplo to see to tag muons and therefore to know when there is immune and potentially a neutron.

494
00:57:24,560 --> 00:57:34,290
We don't take the event in A. Coincidence when the detector? So there is a big water tank with the central detector inside and as you can see,

495
00:57:34,290 --> 00:57:40,680
all the cryogenic and the cooling is done at a distance, something that we invented within a 100.

496
00:57:40,680 --> 00:57:50,730
So the cryo coolers are on the top floor of these so-called service building next to zero one ton tank, there is a three story about 10 metre tall.

497
00:57:50,730 --> 00:58:00,420
The tank is about 10 metres tall and 10 metre diameter, 10 metre tall building made with transparent walls.

498
00:58:00,420 --> 00:58:05,580
I insisted on that, spending a bit more money so people could see the beautiful things that we put in there.

499
00:58:05,580 --> 00:58:12,540
Because when you go into these underground laboratory, you just see these boxes that just look like trailers and you see nothing inside.

500
00:58:12,540 --> 00:58:17,280
And now everybody loves to come and see and they all stop in front of one thought.

501
00:58:17,280 --> 00:58:25,170
This is not because we didn't have money for windows, so top floor as the cryogenic system with the purification,

502
00:58:25,170 --> 00:58:30,720
the metal floor has the the acute room and also the Krypton distillation column,

503
00:58:30,720 --> 00:58:39,600
which sits on the first floor, sticks up because of a 5.5 metre cryogenic distillation tower to reduce the Krypton and xenon.

504
00:58:39,600 --> 00:58:40,650
And on the ground floor,

505
00:58:40,650 --> 00:58:51,930
we also have the the storage of this large quantity of xenon and the photo tube are the most expensive capital investment of this experiment,

506
00:58:51,930 --> 00:58:56,550
with equal amount of so-called dollars per unit or something.

507
00:58:56,550 --> 00:59:04,980
But so we don't want to lose. As you can imagine, Zain and the money on the Aether has been very effective and you won't be reused for Anton,

508
00:59:04,980 --> 00:59:11,740
although we will add in addition to the new and Cherenkov to the water Cherenkov New and V2,

509
00:59:11,740 --> 00:59:16,490
we're going to air the neutral veto by dropping the water,

510
00:59:16,490 --> 00:59:23,850
the clean water with gadolinium sole using the legacy of all of S.K. And so with the Japanese,

511
00:59:23,850 --> 00:59:28,500
which we have handled recently in the collaboration, thank god,

512
00:59:28,500 --> 00:59:35,280
we have had this additional technology that which we can explore for neutron vetoing

513
00:59:35,280 --> 00:59:41,850
since the lab has quite some strict restrictions about scintillating Earth against us.

514
00:59:41,850 --> 00:59:48,450
So if you might know, given the nice present of Orexin spill many years ago,

515
00:59:48,450 --> 00:59:57,300
we are suffering so no liquids and the but probably gadolinium loaded water will be allowed and we will have our new interim v2.

516
00:59:57,300 --> 01:00:06,840
The neutron V2 allows us to to have actually less than 0.01 neutrons per tonne per year.

517
01:00:06,840 --> 01:00:13,080
That was a xenon one tonne level that we achieved, and that's that was quite good.

518
01:00:13,080 --> 01:00:22,600
But we need to do this better for intone. So inside that water thing is this beautiful detector that I told you already how it works

519
01:00:22,600 --> 01:00:30,780
ton of the 3.2 tonne which need I needed to be cooled and I mean liquefied in this vessel.

520
01:00:30,780 --> 01:00:34,170
Two tons are in the actual in the active volume.

521
01:00:34,170 --> 01:00:44,310
And out of those two tons, we physicalize and do 1.5 one tonne 1.3, depending on the search that we're doing the two areas for the multiplier.

522
01:00:44,310 --> 01:00:48,510
These are trained for two to biome and that's a very low radioactivity.

523
01:00:48,510 --> 01:00:55,830
They're about one of 15 total between top and bottom, and this is our wimp would look like in zero one ton.

524
01:00:55,830 --> 01:01:00,120
Essentially, you're going to look for something which has four four two electron signal

525
01:01:00,120 --> 01:01:05,160
in as one and maybe with amplification is built in amplification in the gas.

526
01:01:05,160 --> 01:01:12,460
We're still talking about a few hundred for two electron for a charge based on what we know from calibration.

527
01:01:12,460 --> 01:01:16,020
So this is our signal will look like you see a lot of copper here.

528
01:01:16,020 --> 01:01:24,840
The scope of the field shaping over the one metre. All the white stuff is Teflon because we use a lot of this material to Peterffy,

529
01:01:24,840 --> 01:01:33,450
both as insulator but also as a structural support because it's a good reflector actually for very deep UV light Teflon.

530
01:01:33,450 --> 01:01:38,670
Ideally, you would like to have water tubes all surrounding the the cylindrical structure.

531
01:01:38,670 --> 01:01:45,000
And this deep issue, of course, is not naked, as it is here, this is just the moment where we were installing.

532
01:01:45,000 --> 01:01:53,130
It's contained in a double walled stainless steel, very low radioactivity still cries that, you know,

533
01:01:53,130 --> 01:02:01,170
the inner vessel and two independent vessels in another vessel insulated with vacuum in many, many forms of mylar.

534
01:02:01,170 --> 01:02:06,000
But you also notice that the outer dome is much larger than what would be needed.

535
01:02:06,000 --> 01:02:11,670
Because we had the vision, I had the vision to go to this next step in an easy way,

536
01:02:11,670 --> 01:02:17,880
changing the innovation and keeping the outer vessel and the other infrastructure, which is what we're doing today.

537
01:02:17,880 --> 01:02:22,080
And to give you a size, I guess, that I do in public lecture, but that's me.

538
01:02:22,080 --> 01:02:31,020
That's that's the size of the outer vessel, the crisis that's selling at the company, checking that was just cut the dome, you know, you have to form.

539
01:02:31,020 --> 01:02:39,300
The steel is five centimetres steel formed into this dome shape and to give you an idea of the size.

540
01:02:39,300 --> 01:02:43,770
And of course, that vessel has to be filled with above 600.

541
01:02:43,770 --> 01:02:49,710
We need about 600000 litres of gas to make this three and a half ton.

542
01:02:49,710 --> 01:02:51,780
So you don't want to deal with all of these bottles.

543
01:02:51,780 --> 01:03:00,910
So we we had to design at the beginning of the project something which was very effective and very reliable of storing this precious material.

544
01:03:00,910 --> 01:03:08,430
So we designed this beautiful piece, which is for storing and also recovering in a case of an emergency.

545
01:03:08,430 --> 01:03:15,420
The precious xenon in both gaseous, liquid and we can solidify is a cooled by nitrogen sphere.

546
01:03:15,420 --> 01:03:22,560
Double world again spherical vessel 70 Bar can keep the pressure up to 70 bars.

547
01:03:22,560 --> 01:03:24,000
So even if there's an earthquake,

548
01:03:24,000 --> 01:03:32,100
which is not so unfortunately uncommon in central Italy there and we can all go underground and there is no nitrogen,

549
01:03:32,100 --> 01:03:35,580
the xenon can be kept in gaseous form in that vessel.

550
01:03:35,580 --> 01:03:42,750
There was a very important cryogenic plant, but of course, the the heart of the experiment is this cryogenic system.

551
01:03:42,750 --> 01:03:46,740
I don't have time to go in detail. That's mostly my group at Colombia.

552
01:03:46,740 --> 01:03:57,750
Using the legacy of xenon 100s in a one ton demonstrator in my lab, we use two to refrigerator with two under lots, so cooling power each.

553
01:03:57,750 --> 01:04:04,170
They are redundant. One to watch is sufficient to keep these three and a half ton call and I work very reliably.

554
01:04:04,170 --> 01:04:14,220
But you see the xenon is liquefied in this through this funnel by this positive refrigerator, but with is not sitting on top of the detector.

555
01:04:14,220 --> 01:04:23,130
The detector is in the water tank, but then is actually driven by gravity only through this long umbilical cord because we want all the radioactivity,

556
01:04:23,130 --> 01:04:27,090
which is, of course, this cryo cooler asking a company to make me cry.

557
01:04:27,090 --> 01:04:31,800
Apollo, which is low energy activity, will cost me years and tons of money I don't have.

558
01:04:31,800 --> 01:04:39,150
So we invented a way to keep the machines far away and cool it at a distance, as we say, and it has worked very nicely.

559
01:04:39,150 --> 01:04:46,080
This pipe is, of course, a very it's part of the detector and is filled with in and out xenon line and of course,

560
01:04:46,080 --> 01:04:52,800
all the cables for the signal and the eyeballs. This is a very complex piece and part of the detector.

561
01:04:52,800 --> 01:04:57,840
So you have the cryogenic system and you also have, of course, the purification system.

562
01:04:57,840 --> 01:05:01,530
Xenon has to be cleaned from, of course,

563
01:05:01,530 --> 01:05:11,040
electron negative impurity oxygen molecules will just if you lose even one electron or to remember that I have only five or six handful of electron.

564
01:05:11,040 --> 01:05:17,130
So keeping a log in a semiconductor free from impurities is a key challenge.

565
01:05:17,130 --> 01:05:23,340
But we have most of these over the time we are using in this experiment, gaseous purification.

566
01:05:23,340 --> 01:05:25,080
We actually vaporise.

567
01:05:25,080 --> 01:05:34,470
We take the gas on top of the liquid and we pass it through our temperature getters for xenon and tun and next generation detector or in my lab.

568
01:05:34,470 --> 01:05:38,550
Actually, we are perfecting no liquids in on purification system.

569
01:05:38,550 --> 01:05:45,990
We are cleaning the xenon directly in the liquid phase with the with the barber Nicholas pumps and different type of

570
01:05:45,990 --> 01:05:54,240
filter in order to be much more effective and fast in passing all these 8000 kilograms of stuff through filtering.

571
01:05:54,240 --> 01:05:57,060
And that is going to be used for Anton.

572
01:05:57,060 --> 01:06:04,920
So the cryogenic plants and again, picture just to show you an idea, but there's the picture of the cloud and this is the sphere.

573
01:06:04,920 --> 01:06:13,100
I mentioned it again. It was my response would be that's why I like it, and that's helping again with my students and postdoc.

574
01:06:13,100 --> 01:06:18,650
I have to be everywhere and this experiment, I cannot be away, so you will see me on every piece,

575
01:06:18,650 --> 01:06:23,660
but not on the column, because Christian priests in name or my best friend.

576
01:06:23,660 --> 01:06:28,550
He's very jealous of his own things, so I cannot be next to his colours.

577
01:06:28,550 --> 01:06:33,110
No kidding. Yeah, there was around, actually. So that's good.

578
01:06:33,110 --> 01:06:42,980
Genevieve installation is a beautiful work spectacularly. It has enabled us to lower the Kryptonians in it to below one parts per trillion,

579
01:06:42,980 --> 01:06:48,060
which is the level that we had projected that we need in order to achieve the sensitivity.

580
01:06:48,060 --> 01:06:50,000
So we have mastered the.

581
01:06:50,000 --> 01:06:59,330
The challenge that we have for next generation and any other experiment, like LG and others, is going to be mastering how to control the radio.

582
01:06:59,330 --> 01:07:06,320
The rhythm, which is everywhere, which is emanating from every surface. If I don't have time to say, probably I'm thinking too much of the time.

583
01:07:06,320 --> 01:07:14,930
The one ton year then went on achieve the longest data taking of a liquid xenon t.p.s.

584
01:07:14,930 --> 01:07:22,460
two hundred seventy nine live days from sometime November of sixteen to February of 18,

585
01:07:22,460 --> 01:07:30,020
with the earthquake in between for which we were lucky because nothing was destroyed, so we could continue running a few weeks later.

586
01:07:30,020 --> 01:07:39,350
So in total, with one point three turn of CO2 so that we selected out of the two ton, we have this one ton year exposure,

587
01:07:39,350 --> 01:07:48,980
which has been used for a variety of searches for both coir and scattering, a wind spin dependent wimp pi coupling and the search.

588
01:07:48,980 --> 01:07:55,580
And the analysis goes on. We are searching a variety of we model that I'm not going to tell you too much about it.

589
01:07:55,580 --> 01:08:00,470
You know, probably the paper is, uh, we blinded those data.

590
01:08:00,470 --> 01:08:04,850
This is the way that the whole analysis would be.

591
01:08:04,850 --> 01:08:11,000
All talk here, but we carried out the first analysis for spinning the pan in a blind way.

592
01:08:11,000 --> 01:08:16,460
And so this is the so-called S two over S1 plot where you see charge versus light.

593
01:08:16,460 --> 01:08:20,600
The blinded region is, of course, what we would expect based on calibration,

594
01:08:20,600 --> 01:08:25,400
when neutrons and other sources where we would expect WIMPs to show up, right?

595
01:08:25,400 --> 01:08:30,890
And so we blinded the they. Then we took quite a few months longer, always than I was.

596
01:08:30,890 --> 01:08:33,590
And when we are blinded, that's what we saw.

597
01:08:33,590 --> 01:08:41,780
And remember that the contours, the red dotted line, if you can see, is more or less where the neutron band would be.

598
01:08:41,780 --> 01:08:45,290
So we end up with this number of events.

599
01:08:45,290 --> 01:08:54,320
We did an ambient profile likelihood analysis and the pie chart on these events is actually presenting the fractional PDF,

600
01:08:54,320 --> 01:08:57,950
the Providence, the functional of every background component.

601
01:08:57,950 --> 01:09:06,140
We studied very carefully, and for it to give room for the cross-section that we thought would fit best.

602
01:09:06,140 --> 01:09:15,290
So when you look at these events and you jump off, join when we did the unblinding and it was done actually Colombia with many institutions remotely,

603
01:09:15,290 --> 01:09:22,100
you could see there's going to be a documentary showing some time actually on the 19th of this month in London.

604
01:09:22,100 --> 01:09:29,720
But you can see my said phase and everybody's said phase because none of these events could be a wimp because if you analyse one by one,

605
01:09:29,720 --> 01:09:34,730
you see that one is too close to the wall or is through electronic records type.

606
01:09:34,730 --> 01:09:45,800
And so. For a Three Sigma, I mean, I mean, we said we set our goal to a Three Sigma, at least kind of excess.

607
01:09:45,800 --> 01:09:52,190
And so we only the what we found is that where is the distribution in space?

608
01:09:52,190 --> 01:09:57,920
Maybe I should show you this, this in the paper when we look at them in space, in in 3D.

609
01:09:57,920 --> 01:10:02,420
We see that some have more, some issue or another issue and other issues.

610
01:10:02,420 --> 01:10:09,140
So we don't call them wimp and we can, of course, do a profile analysis.

611
01:10:09,140 --> 01:10:12,410
And the result is consistent with a new life path.

612
01:10:12,410 --> 01:10:17,690
This is still and so we only could put an upper limit and constrain.

613
01:10:17,690 --> 01:10:19,610
And that is the results that we have seen,

614
01:10:19,610 --> 01:10:27,770
which is the more stringent constraint so far for independent the the one sigma two sigma bend in green and yellow.

615
01:10:27,770 --> 01:10:32,840
These were the previous limits by Lux and pandemics, too.

616
01:10:32,840 --> 01:10:40,490
And so this is the state of the art today, I think is still, of course, is going to be there for a while until the next generation comes up.

617
01:10:40,490 --> 01:10:45,410
And that's where we are about a few times then the minus 46.

618
01:10:45,410 --> 01:10:50,510
But and we have done, of course, for independent and pioneer coupling,

619
01:10:50,510 --> 01:10:56,420
but more recently probably have seen in the news that even if we didn't find WIMPs,

620
01:10:56,420 --> 01:11:04,670
we recently measured, we observed the rarest decay on Earth ever seen in a detector.

621
01:11:04,670 --> 01:11:10,070
This has made a lot of news. And first I was sceptical. They might say I want to find the waves,

622
01:11:10,070 --> 01:11:20,600
but it's true that we have observed these two new trainer double electron capture in Xenon 124 using xenon month on and the way she read the paper,

623
01:11:20,600 --> 01:11:23,690
which is in nature. We made the cover of Nature.

624
01:11:23,690 --> 01:11:31,280
It's actually quite amazing, and it was possible just because the detector is so well understood and low in radioactivity.

625
01:11:31,280 --> 01:11:42,780
So Xenon 124 is one of the isotope essentially of about a kilogram of xenon 124 atoms within the xenon one ton figure on Mars.

626
01:11:42,780 --> 01:11:48,830
So out of this one kilogram. And so very rarely, these two protons take simultaneously.

627
01:11:48,830 --> 01:11:54,830
Two protons take these two electrons from a case of become neutrons and me two neutrino.

628
01:11:54,830 --> 01:12:05,210
And this and goes to tellurium. And this then decay as a lifetime or oflife of 1.8 times 10 to the 20 to no.

629
01:12:05,210 --> 01:12:12,290
The press release a trillion longer than the life of the then left and then the age of the universe.

630
01:12:12,290 --> 01:12:21,230
And that is true is a very rare event. We look forward actually with more data from Zeno One-ton as well because we have more data,

631
01:12:21,230 --> 01:12:28,160
but also with xenon and time to hopefully see also the neutrino less to double electron capture.

632
01:12:28,160 --> 01:12:35,990
That would be amazing. So that gives us something. They gave us quite some boosts and confidence that this detector,

633
01:12:35,990 --> 01:12:43,370
which is through is amazingly good to see are the rare events and not just the wimp interaction,

634
01:12:43,370 --> 01:12:48,410
although I believe there will remain my main dream and not the neutrino.

635
01:12:48,410 --> 01:12:54,650
Sorry, that's my own perspective. But yes, I'm excited, but I want to see this WIMPs.

636
01:12:54,650 --> 01:12:59,130
OK, so this is the recent the most recent result.

637
01:12:59,130 --> 01:13:06,590
They made quite some news, I have to say more unexpected, and I was more surprised.

638
01:13:06,590 --> 01:13:13,370
I should say maybe I wonder what will happen if we because the probability that here is more is is a lot

639
01:13:13,370 --> 01:13:22,880
of nuclear physics and people get very attracted by this possibility of measuring such a long decay in.

640
01:13:22,880 --> 01:13:32,450
But and I think before we can call any and this was a 4.4 sigma, we didn't call it discovery because it was four point four and not five.

641
01:13:32,450 --> 01:13:42,200
So we have more data, but it is a very kind of easy kind of result in my mind because if you're going to have an excess,

642
01:13:42,200 --> 01:13:49,330
these were under twenty six events. I'm never going to run twenty six events from wins because we know unless the curve

643
01:13:49,330 --> 01:13:54,440
sexual is completely wrong and we all made a mistake and we excluded events in the past.

644
01:13:54,440 --> 01:13:58,550
When am I going to see in twenty six events for WIMPs?

645
01:13:58,550 --> 01:14:04,910
So it's going to be very tough, probably to convince ourselves and the world that we have a signal from wimp.

646
01:14:04,910 --> 01:14:07,010
But we are going, we're not giving up.

647
01:14:07,010 --> 01:14:14,720
As I told you, we are building xenon and tunnel and essentially to make the story short, because I'm running out of time.

648
01:14:14,720 --> 01:14:20,210
These are the we are building a new detector and the new crimes that in fact,

649
01:14:20,210 --> 01:14:27,170
I'm going to tell the fabricator just tomorrow to check on this crystal and the liquid xenon to the situation.

650
01:14:27,170 --> 01:14:36,140
And the goal is to to actually reuse the infrastructure that we already tested well within a month on by building the new detector.

651
01:14:36,140 --> 01:14:42,540
Yes. But this liquids integrity fixation is going to be vital because we are running now with maybe 100 standard

652
01:14:42,540 --> 01:14:50,910
litres per minute when we purify gas in liquid phase because the gas to liquid ratio is five hundred and fifty,

653
01:14:50,910 --> 01:14:58,020
he takes one of 50 litres of gas to make one litre of liquid with a density of three.

654
01:14:58,020 --> 01:15:05,340
So if we can purify in the liquid phase, we are going is the equivalent to circulate a 5000 standard litres per minute.

655
01:15:05,340 --> 01:15:12,660
This means you can clean this large mass relatively fast and get because before you can search for anything,

656
01:15:12,660 --> 01:15:16,620
actually you have to drift discharges in this detector.

657
01:15:16,620 --> 01:15:23,180
And so the purity of the quality of the material is essential. This liquid purification system is being built.

658
01:15:23,180 --> 01:15:29,670
Going to check on that, I mentioned the neutron V2 with the gadolinium due to water using the same thing.

659
01:15:29,670 --> 01:15:37,670
And the other major contribution again with my friend Christian in the Muslim group is going to be a raisin distillation column,

660
01:15:37,670 --> 01:15:43,020
had a dedicated column or so cryogenic to remove the autoremove.

661
01:15:43,020 --> 01:15:50,280
To read Yeah, to remove some of the source type of the type of sources of rain from the detector itself,

662
01:15:50,280 --> 01:15:58,890
which is the ultimate background that we are facing. So we want to get there, as you know, an order of magnitude better than zero one ton.

663
01:15:58,890 --> 01:16:05,460
Of course, we are not alone. I like to show this way, maybe by 2025, because we will need maybe 20,

664
01:16:05,460 --> 01:16:11,030
20 tonne your exposure at least four years of running with them, mass and the a z.

665
01:16:11,030 --> 01:16:17,100
Of course, you know, in this country, very strong and in us, we all friends, we are competing now.

666
01:16:17,100 --> 01:16:22,260
We're all happy that we are doing both in the end zone and intellectually because there is nobody else there.

667
01:16:22,260 --> 01:16:27,630
So you better guys do it fast because we need to check on each other.

668
01:16:27,630 --> 01:16:36,540
And then there is panda eggs. The Chinese keep going on. They own these Appendix four for TON, which doesn't make much sense, to be honest,

669
01:16:36,540 --> 01:16:43,080
except that if we both fail healthy and, you know, Nantong and then we have the liquid argon,

670
01:16:43,080 --> 01:16:53,940
we have Christiane and Co. I hope they move fast 20000 kg and beautiful detector with liquid argon silicone for the tube readout,

671
01:16:53,940 --> 01:16:58,410
which is being built, but I'm pretty sure it will come later than that.

672
01:16:58,410 --> 01:17:04,290
And then ultimately the Darwin if we're going to do that. So this is where the game is going to be played for.

673
01:17:04,290 --> 01:17:09,480
They have mass. I didn't tell you about the rumours with where there's a lot of excitement and

674
01:17:09,480 --> 01:17:15,300
beautiful technologies which are more even table talk smallest vernment with CCD,

675
01:17:15,300 --> 01:17:21,810
with lots of from demick to Sensei to whatever that keeps going and we need to search everywhere.

676
01:17:21,810 --> 01:17:33,000
But for every mass, for high mass winds, I think the game is going to be played by the liquid xenon and hopefully by the liquid are the experiment.

677
01:17:33,000 --> 01:17:35,880
And so I will conclude, yeah, no need for conclusion.

678
01:17:35,880 --> 01:17:43,050
I just want to reiterate that we're not going to sit as the new double electron capture has shown recently.

679
01:17:43,050 --> 01:17:55,620
We have a hole in principle, a rich science that we can do with this very low background detector massive detector, including, of course, neutrino.

680
01:17:55,620 --> 01:18:00,180
I mean, my dream would be supernova seen an incoming.

681
01:18:00,180 --> 01:18:24,170
Thank you for listening. So.