Thanks, Ruby, for this. Nice introduction. Glad to be here.
And I tried to tell you something about what the LHC can really tell us about dark matter.
Um, but before I do this, I think I have to recall of what this the evidence that we have for dark matter.
And all these evidences are not really in a laboratory, but they come from gravitational interaction.
Okay. And these evidences come from different sources.
And what I think is important that you should take from this is that we can really look at different astrophysical
observations at very different length scales in the South here at a very small scale at that spiral galaxy.
And this is one of the first evidence for dark matter.
So if you look at the velocity here is a function of the radius of this galaxy.
Then what you would get from Newton's dynamic, if you go farther away than you would do,
would tell you that you should see a velocity that falls off as one over the square root of the radius if you have a disk.
So if this off the map, the visible matter here stops its stuff.
But what you see is that it is really very, very different here.
So you have first here what you would expect,
but then that the observation that deviates from your prediction and you reach a constant instead of one of a squared off falloff.
So this kind of tells you that there is some dark stuff, meaning that it doesn't emit light.
Yeah, but in the end, it takes gravitational and there's more stuff in this galaxy that you can see.
Okay. Now you can go to high to larger distances and you can look at not only galaxies, but you can really look at the clusters of galaxies.
And one of these clusters of galaxies is called pallid cluster.
These are two clusters of galaxies that merged and passed to each other.
And this is what you observe if you look at the mass density contours.
So here's the density profiles. So the masses are mostly here and here.
And this you get from gravitational lensing. And then you can also look at that X-ray image and you see that the normal matter radiates here.
And this is located here.
So you see that these things at this place, which tells you that the mass density and the density of the visible limit, that doesn't really line up.
Okay. What they can also learn from this to some extent is that these additional metal matter has essentially leafless interactions.
So it simply pass through each other. But this other vital matter is slowed down and radiates off.
Okay. Finally, you can go to a larger distance into the last large scale.
And you can even try to simulate this.
You know, what happens to the evolution of the universe if you simply put a dark matter profile and also some dark energy into it.
And you can put it on a computer. So we have a huge number of particles.
And then you simply solve this numerically. Okay.
You start that early time. So, yeah. So 0.05 years.
And then you turn on this simulation. And the idea is that you want to have at the end something that looks pretty much what we observe.
Okay. And what you see, the final picture will depend on how much matter,
dark matter and how much stock energy and how much normal matter you will put in here.
Because, for example, if you have more dark matter, things will there will be more gravitation and things will clump more than they should be.
So let's stop this. This is what you see.
Okay. So you start with a uniform density, and then due to gravitational interactions, things start to clump.
The universe is expanding. You don't really see this here.
But now you see that you create some structure.
You see these filaments that arise. And then at the end, you see that you have a lot of structure here.
And as I said, if you put more dark matter in, you would get more.
This all would become more clumpy. Okay. So it wouldn't really fit nicely with the observation.
Yeah. Okay. It also depends on how you what kind of dark energy you put in.
And if you combine these observations,
then you can come up with really kind of an idea what is the content of the universe and the content of the universe?
You can depicted in such a pie chart. So for a few percent of ordinary matter, this is what we are made out of.
Okay? 23% is dark matter and the rest are essentially 75% or 74% is dark energy.
Okay. This is the most mysterious thing that nobody really understands what this is.
Yeah. But I will only talk about the dark matter.
So 23 plus 3%. Okay. Because the other thing nobody understands and I don't dare to really speak about that, something nobody in the States could.
Okay. So but what this stock mate.
So there's, I think, convincing evidence that this dark matter has gravitational intelligence.
But that's not enough for me, at least. Being a particle physicists, I think, is not enough for me.
What I really want to know is, is that particular and how does this fit into a particle description?
So what do we know? If you think about a particle, okay, we know this is already due to its name, its stock,
its nutrients, so it doesn't interact with photons, for example, or only a little bit.
Really, not very much. It is massive, okay.
Because otherwise we would not see it in the evolution of the universe if water into gravitational B, but we don't really know how massive it is.
It could be electron volt. It could be t v scale.
Yeah. So we really have no idea. And it is still around today.
So this means it's either fully stable or it has a lifetime that exceeds the age of the universe.
So it must be some kind of a long lived particle that hasn't decayed so far.
Then we can look at the standard modeller and this is already what you saw.
We have these various particles. Nothing in the standard model of particle, unfortunately, fits this profile here.
So there's no particle that we have in the standard model that has these properties.
Okay. Good. This means that essentially we have to go beyond this standard model and introduce new physics.
Yeah, and that's what I tried to tell you about.
So what we want to do is really we want to somehow fill in this question area.
So we want to we know it into X gravitational, but we have no idea.
We don't know it's mass, we don't know it's spin. We don't know it's life time.
We do not know if it has weakened the x if it isn't the X with WS or SATs.
Yeah, we don't know that.
We don't know if it X if the Higgs, we do not know if it interacts with blocks and gluons with leptons, if it's a tell me relic.
Yeah, we really don't know that. I mean, we have essentially no knowledge about it, a part that it intersects gravitationally.
So this is something that, you know, you need to do experiments in order to fill this in here.
And I will tell about various experiments a little bit about essentially all combining those experiments.
I think you can really feel or tick all these boxes and fill in what the what it is.
Good. So what are the particular probes of dark matter?
They are essentially free ways to search for dark matter before a human built detector.
So the first search strategy strategy is called indirect detection.
So the idea is here you have a dark matter particles, which I will always call ICS, or if you speak Greek, it would be exciting.
And then you assume and this is this this is due to all of this methods that you can look at that there must be some intersection between the stock,
MIT, the particles and the standard model particles. So there must be some coupling, otherwise we can never see it.
Okay. And I.
I simply parameterised this by this blob is a kind of a black box, and something happens there, but we don't really know what happens now.
And the first thing is that you have these dark matter particles and you annihilate them and you generate some standard model of particles,
for example, photons. So you have this thing and there's a small copying somehow of the stock method, two photons, and then you look for photons.
And this is, for example, what is Fermi's telescope a satellite is doing.
So it looks and tries to detect something. For example, it looks for gamma ray lines.
So this would be a line of bump sticking out of a background, essentially flat background.
Okay. The second possibility is now you can somewhat take this blob and turn it around.
Yeah. And the second possibility is called direct detection.
What you would look at there is a scattering of dark matter on standard model particles.
Okay. And this is something you can do, for example, in lacks detect the way Oxford is involved.
So the idea is that the standard model particle comes in here.
His cat thus on in the detector produces a photon.
And then you have electric field here and you have photo multiplier sitting here.
Yeah. And then you get some a cascade of this photon of electrons and then you detect this.
Yeah. So you start with a very small signal, and then you look at how this involves the time.
And this the electrons move up here. They produce largest kinetic.
And from the way how this is how did this signal and this signal relate you?
Can someone feel something about the energy of this that has been put from this particular into the detector?
The last thing is you can again to undo the diagram around and you start with standard model particles
and this is what collider switches to and the you you take protons or it could also take electrons,
smash them together and then you look at what happens.
Yeah. And you look for dark matter particles. Okay.
And this is what is done at the LHC yet. So some people might have thought that they are already some hints of dark matter.
And these hints came from both indirect and direct detection experiments.
So there are many of these experiments and some of them had some small deviation from what is expected.
For example, this is Fermilab collaborations.
One has to say that this collaboration didn't really claim evidence, but theories that analysed the data did, and they found a bigger number about it.
So let me tell you what. This yeah. So they look at events essentially, and they look at a model, a photons at a certain energy.
And and this is kind of the background that you would get.
And then you see a little bump sticking out.
I mean, it's very not really I mean, it's not a huge bump, as you can see.
So this if the experimental collaboration analyses this data, they find the evidence a local significance of something like Three Sigma.
Yeah.
So this is certainly not proof that this is something, but it's I mean, could be a hit, but one should not really take this maybe extremely seriously.
And a second a second evidence or potentially hint for dark matter is comes from CDM SE, for example.
So they have, they look at this a direct detection experiment.
They see that there are three events of really a lot of events that could be dark matter.
Okay. What they should also see is that essentially that detectors only sensitive up to this line.
That's only sensitive to here. And these events sit right there.
Okay. I'm not an experimental physicist, but I assume that, you know, and this is also very vague.
It's very, very difficult to understand the to take their value,
understand the detector well here at the border of your detection, it's probably very difficult.
Yeah. And another thing is that one has to say is that the other experiments are a little bit of in conflict with this observation.
Yeah. So they don't really fit together if you put them all in the same plot.
Okay. So I think it's fair to say that given this large backgrounds in both cases and also the fact that in the case of both indirect detection,
direct detection, you cannot really switch off.
And on the second meaning, we cannot really control influx of dark matter.
Yeah. So we have no control of the experiment itself.
It's very difficult that you can say that this is really a hint of dark matter where essentially possible.
And this is, of course, something that you can't do it, the LHC, because it can essentially turn the protons off and on the beam off and on.
I can't regulate the flux of dark matter or indirectly if it's there.
So this is something it's a really more controlled environment if you want.
Okay, good. So the idea that the production of dark matter there she is as follows.
Yeah, if dark matter particles sufficiently light meaning they should be below the
TV because otherwise we don't have enough energy to produce simultaneously.
And if the couple two quarks influence, we should be able to produce them at the LHC.
So you should see them in the atlas detector. Essentially, if you are lucky.
And by studying the dark matter production, proto proton collisions we are testing.
What we really do is we test the inverse of the process that kept that metal in trouble equilibrium in the early universe.
If you're very lucky, we will not only find dark matter so these x particles,
but there might be a really other states of toxic OC that somehow talks to this dark matter particles
and they are no longer present in the universe because otherwise they would be if they would be stable.
It would also be consist of dark matter. But they have decayed already.
But they could be could give a link between this hidden sector, between the toxic and the standard model.
Okay. So there might be even more than only one particular might be a whole slew of particles, and one could in principle see all of them.
So how do you see the invisible OC? So if the diameter, the particles interact the index very weakly.
Okay, this is already clear. So you will not though what will happen is they will fly out of the detector.
So you will produce important you fly out. This is pretty much what you what happens to neutrinos.
Yeah. For example, if you produce neutrinos, the intake so weakly that they fly out of the detector and you don't see anything.
Okay. A way to see them.
They are essentially two techniques. One way to see them is that you look at missing momentum.
So how does this work? You look at addition to standard model radiation.
So for example, this initial standard model particle in the initial state radiate off a photon.
Okay. Okay. And then you look also, if your event contains some missing momenta.
Let me show you an event that shows this quite clearly. Okay.
So this is the atlas detector again. So the beam is going into the black blotted out, but.
And this is sliced up. Okay. So you see this thing here is transverse to the beam.
Okay. And you see that there's a spray of particle here, which is called a chip.
So these are gluons and quarks, and they have energy and momentum.
And you measure this energy of momentum here. Okay. What is also see is that there's nothing here.
Okay. So there's some kind of problem because it looks like that energy momentum is conserved.
There's something here, but nothing here. Okay, good.
Of course there's something here. Uh, and this is this missing momentum?
Yeah. So by measuring this. Yeah, what is called a more low trait event.
Event that is essentially only one gluon or one chip.
You can infer that there must be something here. And this, for example, is probably a neutrino.
You produced two neutrinos in the fly out of the detector, but it could also be dark matter.
Okay. You don't know. The second possibility is slightly more complicated.
But it's also very interesting because what you would do here, you would not directly produce this stock, met this or this state,
but you would produce a partner state, and then this partner state would decay into the standard model and the dark matter.
Okay, this is another possibility and you will see later that this is, for example, realised in supersymmetry.
Okay, good. So this is the other possibility then this depending on how this popped the case has not this very nice and clean signature.
Yeah. You have more activity in the detector. You have what, threats and so on.
Yeah. So it's maybe more difficult to really pin that down.
Good. So, like, Juan and, uh, uh, Julia told you we have seen the hicks and the hicks essentially was banned.
Ponting. Yeah I saw. He has again this craft that has been showing this is the events is a function of the invariant mass of
the photocopier and you see this little nice pom pom and if you saw many you see it's a clear signal.
If you do this for the SAT, if you have two sets and indicate to two leptons, you do not even have to assume hidden.
The band really sticks out of the background. Okay.
And. To give you an idea, I now compare this situation to what it will look like if you see dark matter.
Okay. Also notice that this is a linear scale here.
So it's a number of events in the media landscape. So this is what you see if you have a linear scaling.
So here, yes, the missing energy or the missing momentum.
Red is the standard model background.
This is essentially if you produce in this case, a set plus a chart and this set decays to neutrinos, then you see a dark matter signal, which is hot.
You can see this is this green stuff, okay?
But if you get furious, that's easier. You simply turn to logarithmic scaling and everything becomes completely obvious.
That's all. You see that now there is in the tail region and that's a qualitative search area.
You see that there's a clear and large deviation.
Okay. Of course, it's very misleading because now this is ten to the minus two.
Yeah. So there's essentially no event there. But yeah, that's how it is.
So. And this tells you that this is really it.
I mean, it's really more complicated than the Higgs. Yeah. In some way, yeah.
Because you really have to understand this background even better than you did in the case of the.
Of the Higgs. Good. So the question is really, if I experimentalists,
how well can I measure the few events sitting in the tail and the furious should ask how they calculate these small numbers.
Yeah. So the question is really how precise do I have to know all these things?
And of course, the fear is usually we don't do this, but I didn't find a different picture.
And it's sorry for this. Okay, so how so?
What do we have to know? What do we need to know?
I mean, one thing is that we really need precise predictions, meaning precise standard model of prediction.
And they involve a lot of ingredients. So you need the expertise of different people.
So you need the expertise, for example, of someone that knows how to compute this here, the pot and distributional functions,
which tell you essentially if you ask for a Coke and that given momentum, how likely is to find this Coke in the proton?
Okay. But then what happens is then you have some kind of a hot scattering process.
So here I show there's a standard model event that would give rise to a jet and missing energy.
So you produce a set both on and on, for example, and then they set the case to neutrinos.
Those fly out of the detector. And you have to compute this.
Either you can compute this at three level or if you are really good, I like to it, for example,
then you can do this at Newport are you add new ones and so on, but it's not enough.
So then what happens is that these gluons radiate off more gluons and also quarks.
And this is called a potentially. Yeah.
So typically you have some numerical code that does all this, so it computes all the emissions of additional gluons in a certain approximation.
Okay, finally, what you need is you don't see a clue one and you don't see the quark in the detector.
What you see at the end, pions, leptons and photons are.
So you have to modernise this cluster, these events.
Yeah. So out of the gluons, you have to make chips hot or nice, everything, and then even have to include decays of these things.
Yeah. So you see, it's a very complicated process. It involves a lot of calculation, different techniques.
Yeah. And but you really need it because otherwise you will never be able to sum up, figure out what this is seeking out.
What is the background? Okay. Good.
What you also need, of course, is you also need a theory to describe this dark matter into action.
Yeah. So you need the standard model in order to tell you what the background is.
But you also have to you need an idea of what this dark metal fury can look like.
And the idea is that, well, it's probably very likely that with this free search strategy strategies, if you only take one of them.
Yeah. You cannot really figure out, even in the case of a discovery, what are these, all these properties,
what is the mass of the dark matter, the spin of what this how does it intersected so on?
You probably need more of the all of this experience, all of this search strategy to really fill in all the gaps.
And then the idea is that there's a certain complementarity.
Yeah. That if you find evidence for dark matter in one type of search, then if you have a field,
you can also predict what you would expect in the other kind of search.
And then you can see that whether you see something or not.
And in this way, by combining this information, you can try to kill mortals or say this is not the correct description and so on.
Okay. In fact, there's really no lack of theoretical models because, I mean, furious or rather creative.
And so there can be a lot of theories of physics beyond the standard model.
There's, of course, supersymmetry. There are some kind of extra dimensional furious with either of warped X that I mentioned
or a universal X that I mentioned as the as things called little hicks models.
It could, of course, be an action. This, for example, would be something that you would not be able to detect at the LHC.
So a very briefly coupled particle. Yeah, yeah. So you would need a different experiment for this could be also some kind of neutrinos.
There's some asymmetric dark matter that some have worked on.
So there's really a really a variety of ideas of new physics.
And very many of these various, in fact, do have a dark matter candidate.
Yeah, it's not difficult to make a new physics model and to have a dark matter candidate
is actually the only thing is that you need a symmetry set to symmetry.
So asymmetry between X and minus x and then this is a stable particle and this is easy to cook up in essentially every model's okay.
So you can either look it in this way, but this is you see the cartoon that was made by Tim Tait is a very.
Yeah, yeah. It would be better if you have some kind of a guideline and I think you can cook up
a guideline so you can somehow look at the spectrum of dark matter fairy space.
So let me explain this a little bit. Okay.
What you can do is you can really look at a complete model, a complete theory that contains the dark matter and in general, also a lot of other stuff.
Okay. So these are models like, for example, the minimal supersymmetric standard model,
like universal extra dimensions and also like little Higgs field where you have a potential dark
matter candidate and then you have a slew of other particles that are not needed for dark matter,
but maybe for maybe good for other purposes. Okay, then you can make it less complicated.
And that would explain this. You could talk about simplified models.
Yeah, this can be, for example, said primordial, obvious and heavy part of the suppose on a dark photon you can talk about squawks l Higgs particle,
and then there's even a even less complete option and the even simpler option that do talk about effective field theories.
And also we'll discuss this a little bit. So let me talk about this part of this spectrum, which are the complete series.
Okay. And complete.
Really, it's complicated. So what you have to do is you have to.
At least add another layer to the standard model.
Yeah. So he has a standard model. And in this picture I added the particles that you have in the minimal supersymmetric standard model.
Okay. So for each particle you get a super partner and this is the same and you also get the additional excess.
Okay. So you have really an enhanced spectrum of particles.
Okay. In total. It turns out if you look at how many parametres this adds to our models, it's more than 100.
Yeah.
And fortunately, many of these are hundreds have essentially to be zero because otherwise it would be in conflict with other observations we made.
So it boils down that in the images. M Typically what you have to consider are 20 additional parameters that can be relevant for dark metaphysics.
But you already see that there are 20 parameters, and depending how I choose this,
you can get it can get very different observations and very different.
Collider Animal ology. Okay, so what is how can you take, for example, production of Dark and the Emesis and they are very many ways.
But let me talk tell you about one way to do it.
Okay. So one way to do is that you have the proton and you strip of some gluons,
and these gluons produce the the supersymmetric partner off the top, which is called the top squawk or the stop.
Okay. And you produce them. And these are dedicated to top quarks and dark matter.
So missing energy. Okay. And this is one possibility.
And now you can try to look or people look for this in the atlas again, for example.
And this is a really simplify fix now quite a bit, because this can depend on a lot of parameter.
But I only show this up kind of a slice of this higher dimension with paramount dysplasia.
So here's the stop mass. Okay.
And here is the literally enormous mass and all the other masses I don't show which could in principle contribute to this.
What you can see is that, first of all, these different coloured regions correspond to different search strategies.
Okay. You really look at different final states, okay?
And you see that even if you do this, then there are some gaps here.
Yeah. Which you cannot probe. So all this coloured things, these are excluded, essentially.
Yeah. While everything right is not excluded.
Yeah. And even in such a very simple situation, due to kinematic reasons, there is no exclusions here.
Okay. If you look at the overall scale that we can probe or that the LHC in run one was able to probe,
then you see that if this dark matter particle is heavier than around 250 GV, then it's all and probed.
Okay. And then I should put this into the context that the,
the fact that they did the most massive standard model particle, that being the top quark is 175 TV.
Yeah. So you see in this case, you really did not probe very heavy objects.
Yeah. So it's only a little bit that you got that you have already probed in the standard model.
So what are the, what are the possible improvements of this.
So people started this is the Atlas simulation. And what you essentially see is that by running the LHC, it's high luminosity.
Yeah. At the end of its run, you will be able to to push this up to 600 feet.
You've also got gain effect of more than two. Yeah, but 600 TV is still not really a huge scale, right?
It's not free TV. Okay. This tells you also that this is very complicated.
And yeah, people at work have to work very hard on it.
Good. So let me now go to the other end of complexity.
And this is effective field for you read descriptions and this is really effective means easier because what you
really do is that you assume that the dark matter particles are the only new states that you can produce at the LHC.
Okay, so what you assume that you are new model has a spectrum like this.
So here's a standard model. Yeah.
Here a little bit up in the mass is this dark matter candidate and then there's a mass gap and then you have heavier states.
Okay. But they are not accessible at the LHC directly.
And in such a way you can describe this production of dark matter in an effective way.
And the idea is that you there's a systematic way to remove these particles and capture their interactions with the dark matter in a systematic way.
And essentially, the idea is that you do what you did for the Fermi theory.
Yeah. So if you are at low energies, you cannot see the W, but it looks to you like a for point into actions.
And the same thing you can apply here. Okay.
So let me walk you through this exercise here. So let's take a simple model where you couple quarks to a new proposal, one which I call a warner.
So it's a heavy version of the set.
And then you set copies to the stock matter. You write down an expression for this, and this is very simple.
The expression is simply g squared, which is the coupling he had cupping here.
And then there's a propagate that which gives you P squared minus M set one squared.
Okay. And then there's some kind of a structure which classifies you this kind of kind of action.
Okay. Now the idea is that what you do in the case of Fermi Fury,
you assume that this moment he much smaller than this mass and then you can simply do an expansion of.
Yeah, which is not even an expansion. You simply set piece square to zero here and you get something like this here.
Yeah. Okay. Um, that's the idea.
And then at the end, what this mathematical expression has also a counterpart is some kind of a diagram.
So you have a local index here, and this local index will be suppressed by one of the mass, a mass scale, if you wish.
This is the coupling in the Fermi Furia, which is also a mass, a dimension, a parameter.
Okay.
And the nice thing if if this and fury such an effective description is that the information on the heavy states is encoded in a single coupling,
namely this object. So all what is happened here, you kind of parameterised by one coupling.
Okay. And what is happening here? This is paralysed by this local index.
But this is independent of the heavy physics. So you separate it.
These scales. Okay, good.
So what? Now you can do this, and you can do this for very different operator's interactions.
And roughly speaking, what the LHC can probe is this mass scale of 700 TV.
Okay. And you also see that the LHC bound is very good at the best, somehow for very light, dark matter.
And then at some point, if it becomes too heavy, you can simply not have not enough energy to produce this and your balance goes down.
So everything below this is again excluded by LHC.
And now in this effective fear, there's a very simple comparison between LHC, a balance and direct detection balance.
So you can take this balance on the suppression scale, on this mass scale and compute from this the dark matter nuclei on cross section.
Okay. And this is what you find. This is the found that this everything there is forbidden.
And in the case of direct detection, this is excluded by direct detection.
And what you see is that at some point, because the direct detection measures, the nuclear recoil energy.
Yeah. And you cannot measure arbitrarily small nuclear recoil energy is.
Yeah, at some point there's no balance here.
And this is where the LHC is most sensitive to the cross-sectoral area and provides them the strongest balance.
Okay. For other indications is even the LHC can even do much better than a directly Texas uses for spin dependent interactions.
And this is due to the fact that for such an actress you lose the coherence.
So you have scattering on not the whole nuclei but on each of the particles.
Yeah. Okay. And then you see that here.
The LHC balance doesn't really change a lot, but direct detection moves from here to here and it's you're doing much better.
Then the last point I want to discuss, and this is simply that it is also very active here.
Oxford is involved in this activity to define and simplify dark matter models.
And the idea is here that you can also make this a little bit more interesting and you consider
models to contain dark matter and the most important step mediating the intersections.
Yeah. So from this very heavy states, you pull one down a little bit and you make it accessible at the LHC.
Okay. So this means that you can not only produce this guy, but you can also produce this guy at the LHC.
Okay. And this has the advantage that I'd like effective field theory is this simplified model.
This really can describe the full kinematics of the dark matter production at the LHC.
Yeah. The effective you cannot not because for example,
if you probe this mass of this of this resonance that you produced, you will see deviation from the kinematics.
Okay, this you have to pay a price for this.
So in this case, having what instead of a one parameter, you have a few parameters, but it's still not 20.
So typically three or four parameters to describe this.
Okay. Let me summarise so dark matter implies physics beyond the standard model.
And in order to understand dark matter, you need to have a theoretical new theoretical concepts.
And these can either be complete models like the MSM, but it's also fruitful to think about less defined, more hazy sketches of FURIA.
Okay, the structures at the LHC in underground experiments, in astrophysical observations,
they naturally target different parts of the dark, met the fury space, and they complement each other.
Okay.
Once we really have a detection, then I think it's fair to say that we really need all these techniques to figure out what the dark matter really is,
to fill out all the, um, to tick all the boxes and to tell us all these parameters.
And I think that the LHC can really bring these sketches of dark matter to life if we are lucky.
Thank you very much.