So I wanted to say you've got the idea now that although we are called the Particle Theory Group, we don't actually all work on particle theory.
Some of us work on string theory for us, work on mathematical methods connecting to different classes of theories.
It goes by the name of gravity duality or what we just refer to as the CFT correspondence.
Some of us work on things relevant to the Large Hadron Collider and some others work on issues connected with astrophysics and cosmology.
And by the way, there are only eight of us. This is not the view of a huge army of people, but what we do like is we direct with others,
we interact with the mathematicians, we interact with the astrophysics, the particle physics.
And although we are theorists, we also address to the experimentalists in first half of the marriage to them.
So can we help?
So I want to tell you about a sort of a you know, I have a day job as a theorist, but I do also have a second career as part of a experiment,
which I was invited to join now nine years ago, which is this amazing thing at the South Pole.
So I always like to show this thing, you know, you can teach on the back, but every direction points north here.
Okay. And that's where there is this amazing laboratory, which is this in fact, is what's on the surface.
The experiment extends down two and a half kilometres to the bedrock under the pool.
And it's amazing that, well, that physicists actually managed to convince people to give them the resources to build such a detector,
which obviously most of us, including many experimentalists,
thought was folly for many years until the day it came up trumps, which happened quite recently.
And that's what I'm going to tell you about. I will also tell you why theorists are interested and involved in experiments such as
these and what bearing it has on the kind of work that we do here in the role of centre.
So the title is Seeing the High Energy Universe.
How do you see the universe? We see it with photons coming along with past life, and that's all we know about the universe.
And if we plot with this in an ideal detector,
the amount of energy we are receiving as a function of the wavelength or the energy of the photon up
here you see that the sky is really dominated in terms of energy by the cosmic microwave background,
and there is the characteristic brown shape.
And we know that although our knowledge of the universe for many years has been restricted to just this optical band,
it so happens that the sun, our star emits light in that range.
And that's why our eyes are sensitive to that.
We don't see any of the rest of it, but we have been able to open new eyes in the universe, and that started with radio.
That was just during the war. And then microwaves, of course, and then we have gone through infrared ultraviolet.
This is important because distant sources are redshifted, as we said.
So in order to see them, you have to observe in the infrared.
And we just heard about an application of what interesting phenomenon we might see in the ultraviolet and X-ray image.
The final frontier here is gamma rays, but gamma rays can only take us so far.
They could take us to something of the order of ten DV, which is roughly the energy of the Large Hadron Collider,
because then the photons that we are trying to see on the route to us will hit
other photons that happen to be hanging around like the infrared background,
photons leftover from the formation of stars. And they're attenuated.
However, if we use charged particles, cosmic rays, we can in principle see up to 10 to 11 g.
They, too, will ultimately see the background photons as high energy particles because, you know,
from special relativity, if I have a ten to the 11 G, the proton that's the gum affected.
The relativistic factor is ten to the 11 because the proton visa V so to it a microwave photon which
is ten to the minus three electron volt actually looks like you multiply that by ten to the 11,
it looks like a ten to the eight V in other words, 180 photon.
So you are moving so fast that even a soft photon hitting you feels like a hard gamma ray and that would break it up.
And you have the so-called Grizzard Xuxa Guzman effect that they will create a lot of pions.
And those pions would go into neutrinos and those will travel all through the universe.
Nothing stops neutrinos. Therefore, ultimately, if you want to see the universe back to the early universe, you must learn to look at neutrinos.
That's the challenge. The challenge, of course, is that they're very hard to measure.
They're very hard to detect. So the story starts with this guy I mentioned discovering cosmic rays 100 years ago, 101 years ago now.
And that discovery has now been extended in this plot,
which shows you the flux of cosmic rays versus that energy through this 10 to 11 g v that I just motivated for you.
Okay, that's amazing. You can see the number of decades of energy that we been able to explore this domain with the variety of experiments,
some based on the ground, others flown on balloons.
They now fly balloons down there, darting on the prevailing winds, which stay up for days at a time.
And then, of course, on rockets and satellites and so forth.
We still are somewhat uncertain about where this energetic particles come from, why they have exactly this ball or shape.
Although Tony Bell, who is in the Clarendon Lab in the laser physics group,
had a interesting theory as to how they get that spectral shape, which we might be able to soon test.
And the real culprits, we believe, are these most violent sites in the universe,
the centres of galaxies like ours, which have got a black hole that is accreting matter,
shooting objects of plasma, which then evidence themselves as huge radio lobes or gamma ray bursts,
which are the most powerful explosions in the universe, as bright as the whole galaxy.
But we don't really know what they are, except that they also involve gravity.
They involved ultimately the energy of supermassive black holes dragging in matter.
That's the most efficient way to convert matter to radiation. And we believe these are implicated.
But one way to find out what these things are doing is to look into that which is very hard to do optically because things that are obscured by dust,
by radiation and so forth. But you can do it in neutrinos.
And neutrinos are always produced when you have high energy particles interact with matter and they are
produced essentially through the production of particles that you're familiar with by onset quads and so on,
which ultimately decay to neutrinos. And those are the guys we are to look for.
And you can see on this plot that the energy range of the CERN Large Hadron Collider is on the up to here.
Cosmic rays nature can do a lot, lot more than that.
And one of the big mysteries in this thing is to find out how it actually does that.
I should also mention that these neutrinos are actually quantum mechanical.
They oscillate. They are light particles that mix with each other as they propagate the oscillate from one type to another,
as dictated by the quantum mechanics that you have heard about.
And therefore, we have a laboratory for studying quantum mechanics on cosmological scales now, which would be very, very interesting.
So David showed a version of this which is even more spectacular,
which is that to create some of these particles of Planck energy, you'd have to build a collider as big as 100 light years.
For cosmic rays. It is not that impressive. But you still need to build a collider the size of Mercury's orbit.
To agree to that, to the level of the protons that you have actually observed on Earth in the period Ozone Observatory in Argentina,
which has observed particles. And the plot here shows that to just contain such a particle of that, it was enormous energy in a ring.
You need to have a magnetic field as strong as that and then extend as big as that.
The product of the two must lie on that line in order for the particle to even be held in its orbit according to the equations.
David, should you follow this to Exhilarated?
So upstairs we have the accelerator physics said to people worry there about how to accelerate particles to high energies,
develop new techniques, laser fields and so forth. Well,
nature clearly has a lot to teach us that we haven't yet learned how it manages
to do this without the benefit of thousands of trained engineers and physicists.
Okay. But there is the challenge for you. Okay. And here is that it's our pride and joy, and here we are being put to shame.
Okay. Now, the point here that I want to make is what, however,
those particles accelerate these enormous energy dick protons, they would ultimately make neutrinos.
So here is a schematic of how those neutrinos are being made through the processes that I told you about.
And we can make very simple estimates based on how much energy these sources are dumping into the cosmic rays.
We can normalise that to the amount of neutrinos you'd expect because roughly speaking, as much energy goes into the by-product as in the sources.
So whatever energy we can see in the cosmic rays should also be there in the neutrinos,
and we can make estimates of what sort of flux they should have. Obviously, I'm not going to show you the details,
but these are the kind of calculation that we make in order to estimate how big a detector we need to do this.
And turns out that nature has already provided us sources of neutrinos, which some of which are indicated here.
There is the cosmic neutrino background. We just heard about the cosmic background that might also be there somewhere.
This has not been detected. It's too challenging at the moment. But we have detected neutrinos from the sun.
We have detected neutrinos from Supernova 1987, which many of you will remember.
Most of my students are too young, and I tell them 1987.
And that was, well, they're still in primary school or something.
But we have also the relic neutrinos from past supernovae, which have yet to be detected.
But we have neutrinos being made in the atmosphere of the earth.
But that's not the cosmic rays which we can measure, and that is actual data from IceCube.
And we hope that ultimately, if you go to high enough energies,
we'll can start to see neutrinos that we have calculated must exist from active galactic nuclei,
from gamma ray bursts, and from this process that I mentioned, where the protons run into the cosmic microwave background and create pions,
and the process is always the same, which is shown here to gain the proton comes in, hits a nucleus in the atmosphere,
creates a so-called extended air shower, and that creates pions that which ultimately decayed beyond the neutrinos.
Those millions are going through us right now, as are the neutrinos.
Obviously, we cannot detect them because we are too small to do so.
You need a big detector.
We'll see how big when we do the classic back of the envelope calculation, because we know that neutrinos interact very, very weakly.
They interact with the cross-section, which is very,
very small compared to the kind of things we are used to see for photons or electrically charged particles.
But it you know that the typical cross-section is of ordinary bond.
That's why we invented the unit, which is ten to the -24 centimetre square.
This is nine orders of magnitude smaller. Okay? So therefore, this is the kind of calculation our undergraduates do.
How many nuclei do you need? Well, Avogadro's number is big, but you still need a lot of material.
And if you want the rate of events for neutrinos, it turns out that you detect one per unit in a kilometre to detector.
Okay, that's how big you need to get. You have to think big. How do you detect them?
Well, the neutrino come in, hit something and that would create a charge lepton for in this case a Bjorn monstrously long way.
And if they are travelling through a medium, they might be going faster than the speed of light in the medium.
And that would set up a cherenkov cone, a shockwave of light,
and we can detect that with sensitive photodiodes or for the multipliers budding in the detector.
And what you have done is to follow up this thing. You could do it in water.
People have thought of doing it in other media, but we decided to do it in ice because nature has been bountiful enough to give us a lot of ice.
And at the South Pole not you also have ice in Greenland.
That doesn't seem to have the right properties. This one is perfect. Because this is actually a plateau.
This is quite high up. Okay. And you already had the big base station did, which provides the necessary infrastructure.
And in particular, you know, flights can go there regularly, land on skis on the strip.
And this is where the base station is, about a couple of hundred people there, lots of experiments being done, including ones in cosmology.
But our route to work is over here, where you have the icecube detected by deep underground, under ice, rather two and half kilometres down.
What you do is you drill holes two and a half kilometres down with a five megawatt drill of hot water.
And as I show you very quickly, you can implant detectors in the ice before it freezes up, takes about a day,
and then you have there the strings in the ice, which have got the ability to see neutrinos.
And this is just to say, show that obviously I didn't do that work.
Lots of competent people from elsewhere did the work. They know what they're doing.
And however, Oxford is involved in that, as you see it, we have been there for some time.
That's along with people from elsewhere.
So something like 11 countries, it's a relatively small collaboration as far as experimental particle physics is concerned.
Typically, Atlas has something like 4000 scientists.
Okay. But the director itself is a challenge to build.
As I said, you build drill these holes, you load the strings.
The strings carry these so-called digital optical modules, which are very sensitive to tubes made by Hamamatsu.
And they are, of course, remember, the pressure down here can go up to 300 atmospheres.
They have to resist that. And happy to say that apparently 97% of our modules have survived.
And, you know, it's just like your mobile phone. Either it works or it doesn't.
If it works, it will work until the built in obsolescence period runs out.
In our case, that hasn't happened. But this whole area, of course, is an ice that is constantly moving.
And so somebody calculated that by 21, 20 or something, the whole array would have drifted to the edge of the Antarctic.
But, you know, we are doing experiments at the moment. We are fine.
And what we have right now is all the strings in the dice, and there are 60 of these modules on each string.
So you have a gigaton of instrumented volume now.
Now we are talking, you know, size does matter in this game.
We do need to have that kind of volume to be able to get a event rate that's at all interesting.
And as I indicated, you have these detectors looking for the flashes of light, the faint blue light.
That's what the wavelength of radiation is at.
And you detect that in these things and the timing tells you what direction they're coming from.
I'd show you some actual data later, but really we are looking at this so-called charge current interaction with a neutrino exchange,
a W boson with the one of the target nuclei creates a muon that is the we are looking for and of course a local record.
Right. If it was the electron neutrino that is, you know, the signature is different.
We see that. So this is what the Bjorn Neutrino track looks like.
There is a lot of information here. I'll be obviously skipping over all these things, but please feel free to ask me questions later.
So the colour code is actually the timing that tells you which one triggered earlier, which would trigger later.
And obviously you can reconstruct the direction very well. But because the neon is passing through, we can only get a lower bound on its energy.
We can only measure up the amount of energy deposited while it was there.
So here is the timing. Good red means immediately this blue means delayed.
And from that we can infer a lot of other information as well as to the energy of the event.
The other kind of they call it topology have objected that topological needs to articulate, but the experiment is calling them topology.
For some reason they have a different signature.
This is an electron neutrino that created an electron and the electron does not have much of a range.
It is, as you know, a lot lighter than the moon. It stops almost immediately.
So you just see a huge mushroom of light in the detector that's about 100 metres across.
Okay, that's an energetic electron neutrino. We know the energy now pretty well, but the pointing is very pure.
How do you know what direction that blob came from? Right. But we'll see that experimentalists are very clever and find ways to do that.
So we are looking for different kinds of neutrinos that have different signatures.
Some of them make charge leptons, and then they can also have interactions with the exchange, a desired boson rather than a W boson.
These are the so-called neutral current events. Right. In fact,
one of the first neutral current events that established the standard model was found in the bubble chambers photograph just downstairs
with the Dallas centre now is years ago and we therefore have a long association with the history of neutrino physics here in Oxford.
I mentioned Dawn Perkins and others earlier and we are today carrying on the
legacy by looking for these very energetic neutrinos coming from outer space,
which give us both tracks through events such as this, or showers, as you see here,
or cascades, as you call them, which could be a signature of any one of these kind of things.
But you make it all lived on, for example, or electron, but not a view on which would give you a track.
So basically we know the taxonomy of these things.
We know what we are looking for, we know how to identify them. And then the question is,
are we sensitive enough to see some of these cosmic sources that we know must be out there because we see that charge counterparts, the cosmic rays?
And this is the current status we have seen, as I said, neutrinos from supernovae and from the sun.
We have seen the atmospheric neutrinos. We can in principle see the neutrinos from gamma ray bursts and going up to here using the IceCube detector,
because we now have to learn a little more than the GV and MF that you've been using.
These giga be sped up and you have to go further to exa electron volts and then to better electron volts and finally to z to electron volts,
which is ten to the 11 G. Okay, so that's how we load plus six here.
We just extend the energy they give it. Okay.
And we also have the low energy frontier is equally interesting because this is where we can look for dark matter,
which Felix gives such a wonderful talk to us about. One of the synergies you mentioned was then violation of dark matter elsewhere in the galaxy.
And of course you are talking about searching for photons, but photons can get absorbed, neutrinos don't.
So we can look, for example, at the sun, which has been sweeping up dark matter for the last 5 billion years,
which are annihilating inside the sun right now as I speak.
And if we see a single high energy neutrino from the sun, one high energy neutrino C of energies in that range, that would be a tremendous,
stupendous discovery because there is no way that any astrophysical process in the sun can make that it would be a signature of dark matter.
And we are also trying to do fundamental physics with this by starting this neutrino oscillations,
by lowering the threshold of our detectors to a few GV because then we can do experiments
using the free beam of neutrinos that nature has given us made in the atmosphere,
which allows us to probe certain fundamental aspects of the neutrino mixing and the quantum mechanical oscillations
such as the mouse hierarchy and possibly one day the CP violation that might be there in the usual sector,
whether there are single that this new kinds of neutrinos, etc., etc.
So that was all. This was all you know what you put in the proposal and you hope for the best that somebody will fund you to build a detective,
as the did, and so on and so on. But of course, the payoff is after years and years, you finally see them.
And these were the first two events that you saw. You can look at the tremendous energy.
This is, you know, two orders of magnitude beyond that at sea already.
And, of course, being the serious people we are, we call the Bert and Ernie.
Okay? And they made the cover of physical review letters.
Okay. And then, of course, that opened up this possibility that we are seeing cosmic neutrinos.
But the case wasn't yet clear because here is the plot of what we expect to see, for example,
from the process with the protons of cosmic rays run into the cosmic microwave background and that they are called cosmic neutrinos.
And this calculation was done by Marcus Aurelius, who was our post-doc here, and some of us.
And we made the most flexible assumptions we could make about this process, and nonetheless, we could push it up above that red line.
And you see these events like clear above it, not that much clear.
The axis is only about three sigma. It is not enough to call it discovery,
but it's certainly better though rapid date intruders that we are able to see high energy events
for which we do not have an explanation in terms of the so called guaranteed cosmology in flux.
These must be to do with the sources. Okay, so we decided we have to do something about it.
We have to look for these guys.
And the problem is that normally what we do is we look through the earth because when we look up, the cosmic rays are creating so much background.
When you look up, we are blinded by it. Would see that you have to reject one in 10 million events in order to see what you're looking for.
That's because these cosmic rays are creating this huge flux of neutrinos.
And also, of course, they're companions in the process which have a huge event rate upwards.
We need to look down to see them, but then we are not sensitive to the bulk of the signal which is upwards, right?
So therefore what we are really doing is we are following this track of this cosmic
rays that we know do exist and trying to see if somewhere new physics comes in,
a new signal comes in. There is also a signal from the production of so-called heavy flavours like,
you know, button quarks or job quarks, which we know must be there at some level.
We have not seen it yet. But what we are hoping to see is some new flux coming in here, which in this scale, which is energy squared times,
the flux would come out of the horizontal line as distinct from the steeply falling spectrum.
That is the theoretical calculation, that's the measurement. Very good agreement, you have to agree.
But we are looking for something like this and this is our got involved now the name of the of the this
this is okay this may not be as much of a challenge as the dark matter surge that Felix talked about.
But it is challenging all the same because if I look in Zenith Angle,
this is looking up South Pole, this is looking down through the earth towards the North Pole.
And you see that the background of atmospheric nuance is huge.
Okay, so we have to somehow reject these guys.
If you look up, we don't want to see the ones from the cosmic ray directions.
We want to look at the closely Filipinos that are coming behind them.
So we have to basically reject one in a million events because the thing we are looking for is down here and the background is up here.
Okay. Looked impossible. But in fact, it is not impossible.
What we can do is that we can use the detector itself as its own veto.
We can sacrifice part of the altar detector and basically demand that what you are looking
for is not accompanied by a view on which would have been made in the same direction.
And that must be it that produce the neutrino. So we basically throw out any event which does not start in the detector.
So basically, if it if there is any action on this periphery, then we just throw it out.
We just look for what is happening inside the detector.
The argument being that it has to be a neutral particle in order to enter without giving any signal there and then do something spectacular in here.
Right. And we had managed to do this, that when I say again, we I mean, the competent experimentalists on this experiment have managed to do that.
The energy threshold has been lowered down to 40 TV, which is a low energy for us,
although it is still about four times higher than the energy of that at sea.
We look for events which are extremely bright, which triggers, you know, a very large number of output tubes,
which I forgot to mention since I skipped over the details, digitise the signal right there.
So it comes to the surface. It is in a form that I could analyse on my laptop, in fact.
But my shift was a few weeks ago. We can actually run the S.A. from a laptop and wi fi.
Okay. I don't need to go to the pool and, you know, to to to run it.
I mean, this is remarkable. This is the nature of. And it also is good for the ozone layer.
I think so. That's fine. Now what we have here is a possibility of looking at this neutrino flux against this background by doing this clever trick.
But of course, when we do this, we also suppress track like events because track like events are coming through there and predicting them.
So ten to I would expect to find mostly events due to electron and neutrinos which have come in here without an accompanying view.
And I've created an event in my detector. I have sacrificed out of 30%, but that's still a lot of detector left.
And what you see here is I mean, I thought I would really show you some actual data.
So you get a feeling for, you know what, we really work with the kind of analysis what needs to do.
This is the background. And what we have managed to do is to separate this little part here with more than 6040 electron heads,
which do not leave any trace in the outer part of the V2, which allows us to say that this cannot be part of that and this is something new.
This is the signal that we are looking for. Okay.
And although this is not theoretical physics, what actually goes into doing this separation is theoretical physics.
The algorithms that are used have interesting connections to mathematical structures that are used in other parts of theoretical physics.
I could tell you about that in some detail. But let me show you some pretty pictures, because ultimately it's these things that we live for.
So when we did this analysis, first thing we did was we discovered Bert and Ernie, but we found 26 other events.
Okay. And now we have some significance because we see 28 events.
But that expected background is only about of the order of ten events.
So now we do have something which is stronger than nearly five standard deviations.
And if you include those two, it is actually above five. So it's time to well, time to get excited.
Right. And you see that most of these events are blobs. They are not things which have got accompanying beyond tracks.
This one is emission drag, but this is electron or it is, you know, or it could be a neutral colour individual GMO neutrino.
We cannot tell just by looking at that. We have to do a little more work.
We have to ask what that distribution is, energy versus the declination angle.
They seem to be mostly showers, as you see here, only a few attracts, but that's as we expected.
Here are Bert and Ernie sticking out at the Beav.
I mean, this is a tremendously high energy and it tells us that we have found something new in nature.
Nobody has been able to create particles of that energy before, at least in neutrinos.
And you can even from those blobs, this is a very busy plot.
But just to sort of show you that this blob here, you wonder which direction the painted neutrino came from.
Well, if it came from this this direction, according to the red line,
then you would expect the timing of the hits and the photo multipliers to be according to the red line.
If it came the other way, then that would be the blue line.
Then the timing would be according to the blue line. And you can see that the data actually allows us, by looking at the so-called reforms,
to pick out what direction it came from, by looking at this timing.
And therefore, we are able to identify what direction in the sky this apparent blobs came from,
which is, I think that the clever because that then allows us to start doing astronomy rather crudely.
So the first thing is that we have this events which are above the expected background.
Those are those points that you see here. This is the expected background with very conservative uncertainties.
And those tell you a bit more about that in a minute. That's where our contribution came in in estimating that uncertainty.
But, you know, things are not clear. Is that cut off beyond that point?
These are upper bound. So there is no events there. And there also seems to be a upper bounds here.
Is that a gap there? At higher energies, there is the so-called glashow resonance where the electron neutrino can come in, create a W boson.
And are we seeing that? These are all questions that we have yet to answer.
But meanwhile, it has been very rewarding.
Your reported breakthrough of the year as a science, as a physics result, and the science of it put us on the front cover.
That event that I showed you earlier, which is now called Big Bird,
and the distribution of these events in declination, in the direction of the sky that they're coming from.
I showed you already. That's the South Pole. This is the North Pole.
And we see the distribution is in fact quite different from what you would expect according to the background atmospheric neutrinos,
which is this blue line. In other words, this is not coming from a particle that is being made in the atmosphere by some exotic process.
That is a possibility. We can rule that out. They are definitely consistent with something which is isotropic about us.
So that's the first sign that we are on to something that is of potentially, well,
cosmological or cosmic at this interest that might be coming from the halo around our galaxy, which is also symmetric about us.
But they might be coming from extragalactic objects which would by definition be isotropic about us.
And there is a lot of physics that goes in here that I can only allude to at high enough energies.
Neutrinos will be absorbed in the atmosphere. This is showing that attenuation for different energies and that allows us to
make estimates of how many we should expect as a function of the zenith angle,
knowing the cross-section.
And then we can compare that with the data and then we can conclude that what we are seeing is definitely the extraterrestrial neutrinos.
They're not being made in the atmosphere of the earth and they are probably coming from extragalactic objects.
All do currently. We cannot be sure of that. They could be coming from within our galaxy.
Right. And so at the moment, the bottom line is just this.
What does that distribution look like on this guy? Well, this is what is shown here.
This is called the log likelihood. This is a measure of the probability that the event actually came from that direction.
The fuzziness is because the reconstructions are not accurate.
I told you that. Plus minus ten, 15 degrees. So this is hardly astronomy.
But, you know, you have to take a first step. And this is the same thing being shown in different coordinate systems.
So this in this coordinate system, which is the so-called equatorial system, that is the galactic centre,
and there appears to be a clustering of events around the Galactic Centre, as you would expect for something to do the galaxy.
Maybe this neutrinos are from the decay of dark matter. But in fact, one of the highest energy events did come from that direction.
But again, the same. This is the Galactic Centre. Now in galactic coordinates where it's of course at the centre of the picture.
But at this point, you go and talk to your statistics chums and they sort of throw cold water on you and they say,
well, yes, that's what it looks like to you.
But it's not actually true because, you know, if you spend enough computer power doing random realisations of the sky scanning in right ascension,
you find that 8% of the time you'll get a clustering like that just by chance.
Right. And 8% is not small enough for us to think that it is significant.
So what's the answer? Well, you could continue debating about what sort of statistics we should use, or better still, get some more data.
Right. And that's exactly what we are now doing. So we'll soon know whether the source is a galactic or actually extragalactic.
There has been a profusion of heretical ideas about what these events could be due to,
and they are so too small for you to read from the back deliberately.
Okay. Because. Because some of them are very baroque and I would not want to.
So here is testing the DVD with high energy neutrinos. Sup with neutrinos from unidentified sources, the super heavy particle origin.
And you know, some of them have more than one sort of implausible thing died in.
But you know so there are a lot of. Well, I just want to say, people theorists always get excited when these things appear,
because now is a chance to try out some of these new ideas we have had about new physics and to see this survive,
or indeed, they might be responsible for some of these things. So let me just give you the current picture.
I showed you this already. This these have been seen for some time.
These are just conventional neutrinos from beyond on condition that most of you.
But now we are seeing the spectrum which looks flat because this is plotted in energy squared times, the floods.
So if spectrum that goes as one over the energy squared would look horizontal.
And we are seeing this. And this is roughly where you expect events to be.
President Trump Gamma Ray Bursts from active galactic nuclei.
We obviously don't have enough information yet to test those theories in detail,
and we are heading towards the energies where you would expect this guaranteed flux of
neutrinos from the interaction of cosmic rays with the cosmic microwave background.
So things are getting very, very exciting, though.
But let me just tell you for a second, you might be wondering, this is all very fine stuff, but what is a particle theorist doing in this experiment?
Well, uploading a flux here you have some events.
But to convert an event into a flux, you need to know the probability of the interaction of the particulate matter.
Okay. How often does it interact? Now we know, of course, at what rate neutrinos interact when they're at laboratory energies.
That's how you measure it. Okay.
But we are not talking about energies which are 2000 times, 10,000 times higher than anything we have ever had in the laboratory.
So you have to extrapolate how do you extrapolate from what we know in a meaningful and sensible way and estimate the uncertainties?
Because that is crucial to establishing whether you have a signal that is significant or not.
Right.
So I just want to give you a plug very quickly, because I realise we are already over our scheduled time of how it makes sense to be in a department.
But fortunately our neighbours have been doing things which turn out to be very relevant to this.
In particular, particle physicists here have been involved in an experiment called Hera at Hamburg,
which has been measuring a process called deep inelastic scattering,
which is exactly what you are measuring in IceCube, except they have been doing it with electrons and protons that neutrinos,
you can't accelerate neutrinos, but they do it with electrons.
But electrons for most purposes are like neutrinos that are good electromagnetic interactions,
but otherwise they are particles that interact with protons without strong interactions.
And that diagram shows the technical king and are deliberately kept in all this stuff that I'm not going to explain.
Just to impress on you that there is some hard core physics behind all this.
You have to do a lot of work to measure. The probability of a neutrino interacting with the so-called protons within the nucleus, you know,
the quarks and the gluons and their distribution within the nucleus is parameterised by things called proton distribution functions,
which are these quantities here. And those, in turn are related to the measurements that you can make at the large at the heat machine.
So what you have here is a measured in those kinematic variables that I had written on the page,
did the momentum transfer in that interaction and the fraction of the momentum of carried by
the struck button of what range has been investigated by experiments and these experiments,
H1 and Zuse Zuse was the experiment here with people involved as investigated a
much deeper kinematic range than before and found something very surprising.
When you look at the universe at very low volcanics x,
this is the parameter that characterises the fraction of the momentum carried by the struct part on the nucleus is basically made of glue.
This is the glue on structure function which you see here has been divided by 20 in order to bring it down to this scale.
Otherwise it would be up there. The nucleus is basically do this constituent golf that you've heard about,
which make up a proton are entirely unimportant when you look at it in this kinematic region.
But because you can create space in pairs of gluons, it is one of the processes which essentially swamp the nucleus.
So we have to understand how neutrinos interact with that stuff in order to be able to interpret the findings of IceCube.
And we have done that.
We can calculate the cross section for neutrinos to interact with the charge current, for example, as a function of energy with that precision,
by taking the data that I just showed you and extrapolating it to the energies that which are now observing icecube neutrinos,
that acceleration induces some uncertainties.
You have to use the machinery called the dotted group of other parts of the equation, and that uncertainty is reflected in that band there.
And so a lot of hard work has gone into it, a large part of it done by my extraordinarily.
But in order to calculate that quantity and that is now the standard input into all these experiments like IceCube and others,
which are seeking to determine whether cosmic neutrinos exist.
And there is also the possibility that we might be able to turn the table.
Our colleagues who work on the dynamics of quantum thermodynamics tell us that this is what the nucleus
looks like in the terms of the model that we are familiar with in walks rattling down somewhere.
But in this kinematic range, the density of gluons is growing so much that the thing is becoming opaque.
It's like a black disk. You might have phenomena which are non-productive in nature.
You might form a new phase of matter, something called the colour gluon condensate.
How do you test these ideas? Well, let's gather neutrinos of this, guys,
and see whether the predictions differ depending on what theory is the correct theory
of this thing here and here you see that there are clearly differing predictions.
Now, this is an energy of ten to the seven gbps we have measured so far, ten to the six.
But all these models give the same answer. But if you can go up to these energies,
then we can tell the difference between what the physics of low excuse CCDs a field of great interest to people doing one of two dynamics.
And how are you doing that? By measuring neutrinos down at the South Pole under ice.
I really like this this interplay of, you know, very different spheres of activity, which all bear on the same theoretical issues.
But Ice Cube's physics program is broader even than that.
We have already mentioned this part here at the search for extragalactic signals,
point sources, gallery births, etc., etc. We also look for dark matter.
As I mentioned in passing, we look for exotic particles like monopoles which might be caught in the ice because if they are slowly enough moving,
they can get ionised and they can. They might lose energy and get stuck.
We look for neutrino oscillations and not give you much further with this.
But just to mention this dark matter idea, which I alluded to earlier,
the dark matter particles annihilating in the sun can generate neutrinos that we look for.
At least you know where the sun is. So you can just look at the sun all the time.
It just goes above and below the horizon at the South Pole and look to see if you see any high energy neutrinos from it.
So far, the answer is no. And we are therefore able to put a restriction on the rate at which dark matter
particles scatter with ordinary matter in order to be captured in the sun,
which are very competitive with the diet experiments that Philip talked about, that that about Felix talked about earlier.
As you see here, our constraints are way below that. And so far we haven't seen anything.
But who knows very soon. Right. And we can also measure neutrino oscillations because they are coming through the earth.
And these neutrino oscillations have been measured in terrestrial experiments.
But you can see them over the baseline much longer than anybody else, as I again have to skim through this for lack of time.
But you can see that we are able to distinguish between the normal oscillation case, which is this and the oscillations that you find here.
And this allows us to determine the characteristic mass, different square of neutrinos versus their mixing with each other,
one mechanical and the controls that we currently have at this once the red ones here not yet
competitive with the one from the terrestrial experiment minnows which is the flagship bit,
but we are catching up and very soon will have a new extension of IceCube called Penghu, which is the precision IceCube next generation upgrade,
and that promises to be able to do things that nobody can do at a long baseline experiment.
So, you know, we have now got stuck in two fundamental neutrino physics, starting with looking for neutrinos from gamma ray bursts.
And just to end something that I'm particularly interested in.
Neutrinos are produced in this ratio in they're produced to pound decay.
You basically make million neutrinos. No electron neutrinos, no doubt neutrinos.
But as they move through space, they mix with each other and they oscillated to each other.
So after travelling far enough, that issue should be democratic.
One, two, one, two, one. And we can tell the difference between electron beyond and down neutrinos.
So this is what we should see at Earth. But one can imagine lots of processes that violate or disturb the coherence that is
necessary in order for this quantum mechanical oscillations to give you that number.
Right. And they could be something as fanciful as the fact that the neutrinos are coming to us to what looks like empty space,
but especially empty when you look at the blank skin that we heard about from David,
maybe it's the seeding mid-stream of black holes appearing and disappearing.
What happens? Evolution of into a black hole is information lost.
We are touching on some of the most fundamental and discussed questions currently theoretical physics and we have a way to
experimentally probe that by checking whether this neutrino flavour issue is as expected without such decoding influences.
So this is something I'm very excited about. It might take a while to do this, but certainly it's on the cards.
So let me sum up.
We have the first analysis from this amazing experiment which has shown us, I think, the first glimpse of an astrophysical neutrino flux.
And that, of course, as usual, raises a number of questions.
We still don't know any of the details. We don't know the spectrum very well.
The sky distribution is consistent with isotropic. We don't yet know if they're galactic or extragalactic.
We don't know that yet. But we will have twice more data in a couple of months.
We are doing something very interesting to look at moon tracks coming from through the earth
all the way 8000 kilometres across and we are able to do various technical improvements.
So I think it is not farfetched to say that we are really seeing the beginning of a new astronomy,
a new window on the universe where you look not in photons but in neutrinos.
And this in turn interests us because it also provides as possible new proofs of physics beyond the standard model.
Thank you.