 Welch yn ffawr, I'm very pleased to be with people who aren't interested in disposing of bodies. So thanks for coming. So we now have Dr Andreas Korn from UCL talking about the hunt for unknown particles, he works on a project that's notorious for the number of authors when they publish anything. It makes my life a right pain. Thanks so much. Thank you for coming and to allow me to speak about some things that I can do. What I care about, meaning elementary particles, full disclosure, I am a particle physicist and if people sort of ask me what do you do, if I'm sort of in a good mood I will tell them I'm recreating the conditions of the Big Bang, if I'm sort of in a more sort of standard mood I will actually admit I'm trying to make code compile. And I'll see a little bit how things go. OK, so what do I want to tell you about? Well, first a little bit of history because if I want to talk about hunting known particles, I have to tell you which particles are actually known and are there any recent discoveries that we have made and also the big question, the big open question is where do we go from where we are? So one of the particles that we know, well, being at AMF, I suspect a lot of that is known to you already. So if we take any piece of matter, there are molecules in there. So those molecules are hold together. Actually, these molecules are made out of atoms and an atom is nothing but a nucleus surrounded by electrons. We also know that the nucleus actually is made up out of various protons and neutrons and in fact, since a while we know that even neutrons and protons are not elementary particles, they are made up out of smaller particles, which we call quarks. In particular, the proton is made up out of two u quarks, two up quarks and a down quark. And for the neutrons, that is just two downs and one up. OK, so that means our normal matter is made up out of an electron, an up and down quarks. In fact, for that first family, there is one particles that we tend to forget because it is a little bit elusive and that is the neutrino, which in fact was postulated to recover energy conservation in weak radioactive decays. So those four particles sort of make up the first family and that make up everything around us. You, me, this microphone, the computer, most of the universe. But we now actually also know that, funnily enough, we do not only have this first family, we have copies of those, we have three families in fact, and those copies are just heavier versions of those particles. So the electron has a heavier brother, which is the moon, which in turn has a heavier sister, which is the tau lepton. And similarly for the other particles in there. Now, many of those particles we have known for a while, so the electron was discovered by Thompson a very long time ago. So most recent discoveries were the top quark in the mid 90s, which is in fact the heaviest particles that we know, about 175 times heavier than a proton, and the tau neutrino, which was quite a little bit elusive and was found somewhere in the mid 2000s. Well, those are the metaparticles, but they are forces between the particles, right? So what are the known forces? Well, there's a strong force, which as the name suggests actually is strong, and is connecting, binding the nucleons inside a nucleus together, binding the quarks together to form protons and neutrons, and binding in fact neutrons and protons together as well. And the way we are thinking of forces actually is as forces being exchanged by our exchange particles, okay? The way this works is if I'm throwing a heavy ball towards you, I will recall, once you catch the ball, you will recall, and we have created a repulse of four-speed finas. Now if you want to have an attractive force, that's a little bit more difficult, you can go the way some of my colleagues go here with a wall or a little bit more poetic as I usually like to say it, where I'm throwing a ball into plus infinity, and you are catching it from minus infinity, and that way we have an attractive force in there. Okay, so those force carriers for the strong force are the gluons. This being EMF for the electromagnetic field, and therefore the electromagnetic force, the carrying quanta is a photon, okay? Electromagnetism is the kind of thing that produces light, in fact light is photons, okay? The thing that keeps the electron in the atom is responsible for chemistry and most importantly is keeping me on this surface so that I'm not thinking it. Then there is a weak force, and that is radioactive decay, and what is responsible there are relatively heavy weak bosons, the W and the Z, and they are in fact so heavy that they are about 80 to 90 times heavier than a proton. And there's another force that in everyday life we actually think of for almost granted which is gravity, but in fact we have a very hard time understanding how we can put gravity into a quantum theory. I have been some progress is made, but it's still a difficult thing, and if there would be a force carrier of gravity that would be the gravitino, but we haven't seen the graviton, but we haven't seen that yet. Now all of those is what we call bosons, which comes from a property that behaves essentially like a spin, it has the same exchange properties, and those bosons have an integer spin, and that's what makes these particles, and also for example the Higgs boson is a boson. Now if we put all of those matter and force particles together, we get what the particle physicist calls a standard model, and that is sort of describing all the forces, all the interactions between particles around us, and for over 50 years people have been trying to poke holes into that theory, and we haven't really found any major ones. There was one snack that for that theory to work, the W and the Z bosons needed to be massless, and they clearly weren't, was having a mass of 80 to 90 times the proton mass, and the way around this was a very elegant mechanism proposed by these guys in the 60s, a sort of very difficult, if you're the only person that proposed a particle, but you have actually a number of people that really laid the groundwork for that, and then suddenly everybody is only talking about the Higgs boson, whereas a lot of us actually try to call it the Garonic-Brown-Anglard-Higgs particle, but that mechanism created a field, the Higgs field here, and that Higgs field, the interactions with that field would be creating mass, it's kind of a friction, and that friction is slowing the particles down, it's creating the equivalent of a mass. And it also so happens that the excitations of that field would produce a boson, the Higgs boson. Now, the nice thing about that theory is that actually it predicted almost everything, so we have now particles that we think we know very well, we know what possible decay options it can have, and you can see here on the right side, depending on the mass of the boson or on the mass of that Higgs particle, what are the possibilities that it can actually decay on? The Higgs giving mass is coupling to mass, meaning it should be decaying into the heaviest particle that is available to it. In fact, at a mass of about 125 GeV, don't worry about the units, it should decay mostly into a pair of bottom quarks because that is the heaviest kind of particle available. The top quark is too heavy and the other particles are lighter. So, the only thing that was not predicted was actually the mass of the Higgs itself, so we had to look everywhere. Well, as that proposed in the mid-60s, searched for literally every single particle collider ever since, but finally queues a large Hadron collider. Now, the question is why are we looking for these things at actually particle colliders? They are Einstein's most famous equation, energy equals mass speed of light squared, probably one of the few equations that you might find in almost any popular science book, there is only one equation usually. What does it mean that if you are colliding particles, you are creating a blob of energy and that blob of energy can turn itself into other mass of particles? If you think of that in real-life ways, you have two strawberries flying into each other and creating a bunch of pairs flying out. At the LHC, those two strawberries are actually two protons, so two hydrogen nuclei, and we are creating a bunch of new particles coming out of that. That is why I support it, so poetically said creating that energy density, recreating the conditions of the big bang is what I do, even though mostly I make cold compile. So how do we get those particles actually to those speeds? And what we do is, well, using the electromagnetic field and the electromagnetic force, so the simplest way that you can think of that is that we actually just have an electrode with a high voltage, a proton being positively charged would be attracted to the negative electrode and therefore accelerate and gain velocity and energy. In reality, what we actually use is a radio cavity and a radio wave, and you can sort of think of the charged particles surfing along the peaks and troughs of that wave and getting accelerated very close to the speed of light. Now, what does the LHC actually look like? That's sort of a schema here where you see that there is a big tube underground and there are several places where actually the beams cross and we are colliding the particles. And if you're not particularly impressed with the drawing like that, I also have a real, real-life picture for you. What you see in the background here are actually the French Alps, Lake Geneva, and if you look closely somewhere here, that is actually the Geneva Airport, just to give you an idea about size. Now, the whole ring is about 27 km in circumference or, as my London colleagues tell me, roughly the length of the circle line, but the circle line has a lot more delays than this. So, on those collider, we have a number of experiments detectors where we are looking at those collisions. One of those is Atlas. You can see that here underground where the ring is coming and protons are coming from one side and from the other, but Atlas is actually also an international collaboration. I have 3,500 colleagues, if you look from all over the world, in fact also from all over the UK. If you look at the bottom picture, I think I'm somewhere in the top right, but you'll probably have a hard time finding me, but working together with that many people with very different backgrounds is actually quite challenging, but also extremely interesting. So, back to Atlas as a particle detector. So, the way we actually look at these collisions is by having this rather large area quite detailed instrument. And we start, we have sort of a kind of shell structure, so you see that there are protons coming from either side colliding in the middle and it's that innermost part is where we have a tracking detector. That, in fact, is usually a silicon detector with a very similar technology as the camera on your mobile phone. In fact, that's in fact what I was working on. Except that that camera has about 100 megapixels is about 50 centimeters in diameter and about a meter and a half long. And has to take pictures about 40 million times every second. So, that is followed by a magnet that we keep the tracker immersed in, followed by what we call a calorimeter, and I'll talk a little bit about that. Then if you look to the outside, where we again have some very fancy magnets and muon chambers because as it turns out, the muons are the only particles that can actually travel that far. To give you an idea for size, that's about 50 meters long and 25 meters high. And if you look on that side there, you see there are two people standing to give you a rough idea for size. But again, you don't have to believe the drawing. There's a picture. That's a rather old picture, but actually I prefer the old picture that's taken during the construction where you could actually still see something of the structure of the detector. What you're mostly seeing on the outside here, these things with the red bands, those are in fact superconducting magnets to allow measuring the muons a bit. And again, there's a person to give you an idea about size. Now, the big question is, how do those detectors in general actually work? How do we actually trace charge particles passing through there? Well, the secret is ionisation. But as ionisation, if you have a heavy charge particle, that will knock off an electron off an atom, as you see in the top right corner there, and by knocking several electrons, it will lose energy. It will lose most of its energy, transferring the energy to those electrons, and in turn ionise those atoms. Now, with that mechanism, we can use that to actually trace our particles. In the good old days, we would use a cloud chamber, for example, as you can see at the bottom right there, where the charge particles are sort of leaving a trace similarly as a cloud trail that a plane would leave in the sky. But nowadays, in particular, to read out 40 million times every second what we need are electronic detectors, and what we are using are silicon detectors, where passing through particles is actually generating a pulse. Now, ionisational factors are also the magic, if you so want, behind proton beam therapy, where we can use a very dedicated mechanism to treat cancer, or treat localised m-tumers, and as you might know, in the UK, there are currently two places where we are building proton beam centres. One is in London, the other one is in Manchester. Now, the problem now is that if you have particles passing, actually what we measure is not really the trajectory of the particles, but just where they are passing through our sensitive elements, you can sort of see that in white here, and we then need to actually connect those white dots to actually follow the trajectory of the particle. In a picture like that, that's fairly straightforward, and one of the things that you will realise, probably, is that the particles are actually being curved. So the reason for that is that they are charged particles inside a magnetic field, and that gives us an advantage because that way we can actually measure the momentum or the speed of those particles. Think of it if you're playing soccer, if you're like me on a windy day, I essentially have zero chance of hitting the goal because I shoot very, very feebly, the wind will drift the ball away, it will miss the goal. If you have a proper soccer player, they will hit the ball with a lot of velocity, it will go almost straight into the goal. Similarly here, the higher the speed, the more straighter the trajectory. Therefore, by the bending of the trajectory, we can actually measure the speed of the particles. As I said, we can stop particles and measure the energy, and what we usually do is, when we stop them in structures like this, they actually create a kind of shower, and that shower creates light, and that light is proportional to the amount of energy that they have on that we can measure. It's not always that easy because there are often a lot of those trajectories, and as I said, what we actually measure is not the trajectory, but just the hits of the particles. Fortunately, we have a lot of computers available, and in fact CERN is one of the big computing centres in the world, and just to hammer an old story home, that's a place where particle physicists, in fact, invented the World Wide Web. You can still see a not-so-shiny plaque somewhere down in the hallways of CERN, where Sir Bernhard Slee started off the first web server, and I suspect most of you are too young to actually remember the very first web page there. In fact, we not only have one centre, we have computers all over the world because with the amount of data, as I said, we have about 100 megapixel camera, 40 million collisions every second, that is a lot of data, so storing that data, analysing that data, requires a lot of computing. Some of that actually is done very cleverly already on the experiment, so design our own ships to really do some of that processing in the detector itself, but still the amount of data that we store and move is rather large, and what other people might know as the cloud for us is a grid of computers where everywhere in the world, essentially every university that's doing particle physics is having a connected cluster. We also need clever algorithms, and while machine learning neural nets sort of started sprouting up in particle physics somewhere in the 90s, in the early 90s, it recently has become a more mainstream kind of tool to use. Now, if you put all of this together, what are the various signatures that we can find? The easiest that we can do is reconstruct leptons, meaning an electron and muon to a lesser extent a tau particle, where we more or less can connect a track in the inner tracker with a blob in the calorimeters and thereby identify those particles. So there are other signatures, so jets which we can measure in the inner tracker and the calorimeter, missing energy, so there's momentum conservation when we collide the particles in the transverse plane, so if you have particles shooting off in one direction and nothing in the other, that means those invisible particles have to balance the measured particles. So there are particular kinds of jets and bee jets, and in particular, let's say, we can put the quantities of all of those together and reconstruct the possible mass of a decaying particle. Think of it, if you have a coil there on both ends, you have a marble attached. If you have a strong coil, those marbles will go much faster than if you have a weak spring, those marbles will not go very fast. Similarly, we can determine the mass. With that, there was a discovery, so you see that there are accesses in the masses of those decay products that were predicted, and in particular that there was a noble price given, but that is sort of just the back story to actually what I want to talk about. Now we found the hags, where do we go next? That was in 2012, that is six years ago, what have we been up to? Well, the important thing to understand is if you find a new particle, you actually probably spend the next decade understanding what you have found, because you need to really be sure that all the properties are as predicted and that there are no deviations because that could lead to something excitingly new. So in particular, if you look, the most probable decay of the hags boson was into a BB bar pair, a bottom quark pair that should be most copiously produced in the hags decay. In reality, that wasn't used in the discovery, and we only had a few years ago some indication that that was really happening. In fact, only about a week ago do we have a real starting-to-be precision measurement of the process. The problem essentially is that a pair of bottom quarks are strong interacting particles, which means they get strongly produced by other mechanisms and finding that hags decay instead of finding a needle in a haystack. Now, the way to get around to that is you try to make your needle glow in blink, and the way we do that is we have an additional signature of an additional mz boson there, and if you look on the right, you see those two blue cones that is the hags boson decaying into those two bijets, and then there are two dark blue lines. These are two electrons from the additional signature which makes it possible. Well, that is that everything. Okay. In addition to the hags, are there any other problems that we have to deal with? Well, yeah. In particular, on the hags itself, not everything is fully understood yet, and we might need additional theory to help with that. If you look around you, almost everything is made out of matter, so according to the Big Bang, things should have been created in meta-antimetre pairs, whereas the antimeter is gone. Gravity, we deal with that every day, not in particle physics, so better we find a way to actually include that, and I saw a nice book by Penrose on one of the exchange tables, but I think it's gone by now. And then the big question is, did we forget anything? Yes, our universe says yes. It says dark matter, okay? So dark matter, the universe can't even be bothered to interact with you. There is matter that doesn't like to interact very much. What you see here is a picture of the bullet cluster where we take three different measurements, that's what we see, okay? There is the heat generated, or the x-rays in this case, when normal meta-particles are sort of interacting with each other, kind of the friction kind of thing, and then we found this gravitational lensing, those blue blobs, where it looks like of those two colliding galaxies, there are some parts that actually just march through each other, and that is what we think is dark matter. In fact, those of you that arrived here on Friday, you might have listened to everything about dark matter, from a colleague of mine, so you might already be experts, but let me remind you a bit. So the reasons that we think that there is dark matter essentially was first proposed by Fritz Spicci somewhere in the 30s, and then by precision measurements by Vera Rubin of the rotation curves of galaxies, okay? Essentially, if you think of the speed of a conquer that you are twirling, that is determined by the force by which you are holding it. It's the stronger you hold it, the faster you can twirl it, and that force, in fact, is given by the mass in it, in case of a galaxy, right? It's gravity that is holding things together. So from normal theory, what you would expect from the mass that you see is that a rotation speed to actually go down, but what we see is that it stays constant, so there must be a hollow of dark matter to hold it. In fact, we now have supporting very strong evidence from fluctuations in the cosmic microwave backgrounds that tell us that, in fact, the matter that we know is actually just a tiny fraction, just 5%. The standard model, the particle needs to not interact very much. The standard model can't actually provide that, so all the standard model particles fall out of there, which means we need to look for something new. The way we can do that is if we have some interaction with the particles that we know, we can make it, break it, or shake it. Making it means we are colliding standard model particles at the LHC, for example, and create dark matter particles. We can shake it, that's in fact what my colleagues in direct detection do, where we have a dark matter particle hitting a nucleus and that nucleus is flying away, or in the universe, maybe, there's dark matter colliding and annihilating, creating normal matter particles or dark matter decay, so breaking it. So the way we would normally envision that is with a final diagram, I apologize for that, but the way to think of that is that it's a diagram where you have particles coming in, a mediator in the middle and particles going out, and the problem is if you only create dark matter in a collider experiment, you wouldn't see anything because a dark matter doesn't actually interact, visit a detector, but if you're creating something else, then we might see that signature, so in fact we might see some visible particles flying in one direction and recoiling by a dark matter particle. Also possible that such a mediator then decays again into the original standard model matter particles that we know and that would create such an event of two digests, and in fact that is one of the highest energy events that we have observed at the LHC, but in fact that is in accordance with the theories that we have. I think I'm out of time, but I wanted to give you a few chances to get possibly involved. In fact there is data available, so you can have a look yourself. There are challenges to try and identify various signatures at the LHC and there are substantial price money available. These are past challenges, but there are future challenges coming. There is a possibility to get together with people from CERN to work on humanitarian missions, and last but not least a really shameless plug, a colleague of mine that couldn't quite make it to be here has actually written a very nice book as a layman's introduction into particle physics, so if that is your thing, have a look. Thank you.