Full Transcript for The Standard Model and the LHC! in the Higgs Boson Era

00:04:27,540 --> 00:04:33,150 Which are the life radioactive decays so why we atoms decay radioactively we had no theory to explain this. 48 00:04:34,500 --> 00:04:38,130 Moreover, all these particles are fundamental. They are composite. 49 00:04:38,670 --> 00:04:40,200 They didn't have any structure. 50 00:04:40,710 --> 00:04:49,490 And even more important, which is a suitable mathematical language to describe particle physics is quantum mechanics is something else. 51 00:04:49,500 --> 00:04:55,440 This was not clear to many people. Now, let me begin with the first thing that actually this is quantum quantum electrodynamics. 52 00:04:55,650 --> 00:04:59,820 This was well, this is it is the quantum version of electromagnetism. 53 00:04:59,820 --> 00:05:07,500 So electromagnetism was discovered by many people in the late 19th century, and it describes the interactions of charged particles. 54 00:05:07,500 --> 00:05:10,800 We had exchange of of photons, however, 55 00:05:11,190 --> 00:05:16,829 making sense of quantum thermodynamics so making sense of electromagnetism once we called 56 00:05:16,830 --> 00:05:20,730 quantum mechanics was extremely challenging y because you had to apply multiple infinities. 57 00:05:21,300 --> 00:05:27,870 When we try to compute corrections, quantum corrections to electromagnetism, we encounter infinities and how to deal with these infinities. 58 00:05:27,870 --> 00:05:33,360 What have theoretical thought? The force, which took ten years until the formulation of quantum electrodynamics was achieved? 59 00:05:34,230 --> 00:05:39,330 I'm sure these are very beautiful theory because starting from simple rules, which are called the Feynman rules, 60 00:05:39,630 --> 00:05:44,670 we can compute any terms as an expansion in power based on the weak coupling. 61 00:05:44,760 --> 00:05:47,940 The electromagnetic coupling is basically the electron chatter square. 62 00:05:48,360 --> 00:05:49,410 So these are small number. 63 00:05:49,650 --> 00:05:56,700 So you can compute the leading term and then subsequently add more and more complicated attempts, each of which will be in principle. 64 00:05:56,700 --> 00:06:01,170 It's my of the others. They can achieve an arbitrary position, make computing more and more complicated diagram. 65 00:06:01,530 --> 00:06:06,719 So if I put together all these lines and all these vertices and I do the entire in principle, 66 00:06:06,720 --> 00:06:11,190 I can achieve arbitrary accuracy in any any process and actually some of the most precise. 67 00:06:11,440 --> 00:06:15,760 Nations that we have never done have been done with quantum electrodynamics, for example. 68 00:06:15,940 --> 00:06:20,080 These are quantitative, which is called the anomalous magnetic moment of the moon, 69 00:06:20,440 --> 00:06:24,460 which equity is known to an accuracy better than one part in 1 billion. 70 00:06:24,970 --> 00:06:30,310 Imagine this we can compute something with this incredible precision and attack this with experiment. 71 00:06:30,590 --> 00:06:35,319 It's really a major success of quantum theory. Of course, this is not an easy task. 72 00:06:35,320 --> 00:06:39,190 We'll have to compute extremely complicated diagrams which involve complex interest. 73 00:06:39,550 --> 00:06:43,900 But in principle, starting from these rules, everything else is fully, fully predicted. 74 00:06:45,320 --> 00:06:49,160 Now, what about the poor? How they were just how they were discovered? 75 00:06:49,430 --> 00:06:58,640 Well, in the beginning of the century, there were experiments discovered in internal structure of of atoms. 76 00:06:58,940 --> 00:07:02,749 How this this was discovered. Well, so that was the experiment. 77 00:07:02,750 --> 00:07:10,370 There was a theme, a theme for love of God. And then you had this was bombarded with alpha particles, which basically helium nuclei. 78 00:07:10,730 --> 00:07:15,530 And we looked at a ruler for look at the reflection of this of these of these alpha particles. 79 00:07:15,770 --> 00:07:19,370 Right. And by looking at the scattering angles of these alpha particles, 80 00:07:19,370 --> 00:07:24,590 after interacting with their with atoms, they realised that the atom is not like a pancake. 81 00:07:24,740 --> 00:07:26,270 The atom is really odd. 82 00:07:26,270 --> 00:07:35,240 The all the positive charge is constituting a very small volume, which is the atomic nuclei, and then the electrons are around these nuclei. 83 00:07:35,750 --> 00:07:38,810 So this was, of course, our impressive discovery. 84 00:07:39,290 --> 00:07:43,460 Very interestingly, 70 years later, the very same technique was used to discover quarks. 85 00:07:44,300 --> 00:07:51,930 What did we do? Well, in this case, instead of using alpha particles against atoms, we use very energetic electrons and we bombarded a protons. 86 00:07:51,950 --> 00:07:56,480 Right. And by looking at how the electrons were deflected, whereas when they scatter with a product, 87 00:07:56,750 --> 00:08:03,710 we discovered that in the proton the charge is also point, like it's concentrated in small volumes. 88 00:08:04,010 --> 00:08:09,649 And this what is what led to the discovery of of of quarks in there in the proton by the same 89 00:08:09,650 --> 00:08:13,820 mechanism as the discovery of the atomic nuclei by their in their order for experiment. 90 00:08:14,890 --> 00:08:17,980 Of course, the concept, of course, had been known for a while. 91 00:08:17,980 --> 00:08:27,490 Right. Since it seems since the sixties we had the Constitution Park model, which allowed to describe all the all the others as composed by this. 92 00:08:28,960 --> 00:08:33,190 This. Hypothetical particles, which are called the quarks, like example, 93 00:08:33,490 --> 00:08:39,610 the proton can be understood as as composed by two apart and one network and the neutrons one upward to the quarks. 94 00:08:40,000 --> 00:08:44,170 However, these

works were very peculiar, right? To begin with, they had fractional charge. 95 00:08:44,260 --> 00:08:49,900 So they tell us either two thirds or minus one set. And we have never seen a particle fractional, fractional charge. 96 00:08:50,290 --> 00:08:57,280 So many people was a sceptic and they thought that perhaps this is just a mathematical trick to organise hadrons by physical existence. 97 00:08:57,730 --> 00:09:06,500 However, after the experiments that I mentioned here, people realised that they are able to play a good mathematical description. 98 00:09:06,520 --> 00:09:15,420 They are really they have a physical existence and describe their. The structure of Aladdin's soap with just up down a stretch we could describe. 99 00:09:16,110 --> 00:09:24,240 Essentially all known. No. So again, we had the very interesting surprise winning the 73 to 77. 100 00:09:24,270 --> 00:09:32,930 Two new, heavier quarks were soon discovered, the Champ Quark, with a mass of about 1.5 and the bottom quark with almost about five g. 101 00:09:33,690 --> 00:09:38,370 So this is there in this spot here, you can see that their discovery of their channel. 102 00:09:39,060 --> 00:09:42,900 So how these things were discovered, we had an electron positron collision. 103 00:09:42,930 --> 00:09:46,050 Right. And we've vary the mass, the energy of the collision. 104 00:09:46,500 --> 00:09:48,760 And at some point we see that there's a peak. Right? 105 00:09:49,020 --> 00:09:55,020 This peak is indicating that in this collision there is a particle which has been formed with Hamas around three TB. 106 00:09:55,440 --> 00:10:00,269 This particle was called the jape site, which corresponds to a mass of our time. 107 00:10:00,270 --> 00:10:08,849 And so this was the discovery of the Templars in 73 and there is an even heavier support of 475 times. 108 00:10:08,850 --> 00:10:13,230 The proton mass is it's a single particle which is almost 200 times heavy on the proton. 109 00:10:13,650 --> 00:10:17,340 Had to wait until 1995 to be discovered because it's being so massive. 110 00:10:17,340 --> 00:10:24,860 We need very high energy colliders to be to be able to. To detect it now. 111 00:10:25,400 --> 00:10:28,580 So I've thought about quantum electrodynamics, this activity spectra. 112 00:10:28,580 --> 00:10:34,550 But if I can compute terms because the coupling is small, I can just compute 10% expansion in orders of this coupling. 113 00:10:35,420 --> 00:10:41,719 So this, of course, makes a theory very predictive. I thought my Feynman ephemeris I can draw diagrams for any process. 114 00:10:41,720 --> 00:10:46,460 I can compute the corresponding cross-sections. However, the atoms interact strongly. 115 00:10:46,850 --> 00:10:51,920 Right? The interaction is characterised by if like it's coupling is something which is very strong. 116 00:10:52,430 --> 00:10:59,050 So it seems that the model of QED is of, of affirmative quantum field theory is not applicable and that we need something else. 117 00:10:59,060 --> 00:11:03,110 And people working this are extensions of like a theory or its matrix. 118 00:11:03,650 --> 00:11:11,780 However, a breakthrough came in in 1973 when it was realised that there was a theory that could describe the strong interaction. 119 00:11:12,140 --> 00:11:18,440 At the same time, the attractive theory is called quantum thermodynamics, and quantum computing has a very peculiar feature, 120 00:11:18,440 --> 00:11:22,670 which is the following, which is the strength of the strong interaction. 121 00:11:22,730 --> 00:11:29,420 So this is the value of the QCT coupling as a value, as a function of the energy right in the remains able quantum of series, 122 00:11:29,690 --> 00:11:35,240 the value of the couplings around this with the energy. This is the three romanisation group equations. 123 00:11:35,600 --> 00:11:39,350 Now, if you look at low energies, for example, well below the proton mass, 124 00:11:39,590 --> 00:11:43,970 this coupling is very large and the theory is strong, interacting as all the data suggested. 125 00:11:44,360 --> 00:11:48,890 However, once we look at very high energies, for example, 100 times the proton mass, 126 00:11:49,190 --> 00:11:53,690 the theory becomes quickly weakly coupled because alpha is a small number. 127 00:11:54,170 --> 00:11:56,690 And in this regime, what I'll face is a small. 128 00:11:56,930 --> 00:12:02,900 We can just exactly the same techniques as what QED to do to computer, to compute predictions for physical observables. 129 00:12:03,230 --> 00:12:05,540 And this was verified to very, very high accuracy. 130 00:12:05,540 --> 00:12:13,250 So again, quantitative theory is the right language to describe not only the electromagnetism, but also the strong interaction. 131 00:12:14,450 --> 00:12:20,240 So the strong interaction, say, QED, has the photon. In the case of a you see we have the gluon, 132 00:12:20,480 --> 00:12:28,790 which is the particle that made this interaction and is responsible of binding together the quarks in there in the proton. 133 00:12:28,910 --> 00:12:34,400 And this you can understand that easily. So we see that the strong interaction is something that the coupling but also with the energy. 134 00:12:34,490 --> 00:12:41,690 Right. We know that even in quantum mechanics growing with the energy, so it's more energy to correspond to larger distances. 135 00:12:41,930 --> 00:12:45,140 Now, imagine they have two quarks and they have they are very close together. 136 00:12:45,590 --> 00:12:48,860 If they are close, it corresponds to basically large energies. 137 00:12:49,160 --> 00:12:53,209 So the copying is small, but if I tried to pull them together, so I pulled them apart. 138 00:12:53,210 --> 00:12:58,640 Sorry, their distance will increase. At this point, these correspond to lower energies and they will become a strong. 139 00:12:59,060 --> 00:13:06,010 So the fact that the

coupling is large is large. A small energies for large distances implies that we cannot have quarks isolated. 140 00:13:06,020 --> 00:13:08,960 They will always be bound together because this coupling is very large. 141 00:13:09,500 --> 00:13:17,470 Now, the gluon was also discovered but also verified experimental its existence in 1977 and this is called three jet events. 142 00:13:17,480 --> 00:13:21,710 So the theory of the strong interaction predicts that if we collide electrons and positrons, 143 00:13:22,040 --> 00:13:27,560 some of the events that we will see in our detector will have kind of mercedes's shape. 144 00:13:27,830 --> 00:13:32,360 You have to quirks here. And then there's a gluon recoiling and this is exactly what was seen. 145 00:13:32,360 --> 00:13:35,240 So this would be awkward yet quartette the yet. 146 00:13:35,570 --> 00:13:42,080 So again this provided an extra evidence that electricity was the right theory for the strong for the strong interactions. 147 00:13:42,770 --> 00:13:47,270 Now going to the interactions with interactions are something that was having known for 148 00:13:47,270 --> 00:13:52,400 a while because it's allowed to explain the idea of metallic metallic of of nuclei. 149 00:13:52,970 --> 00:13:58,280 Now, in the 1930s, Fermi explained the metallic of nuclei by full body interaction. 150 00:13:58,960 --> 00:14:08,060 So basically you have a neutron and these news on the case into a proton and neutrino and the electron in out for body interaction. 151 00:14:08,270 --> 00:14:15,620 So therefore the atomic number of this nucleus would change by what one unit as modified in better metallic experiments. 152 00:14:16,250 --> 00:14:20,780 So it seems that these are also very different from the strong, from the it from QED, right? 153 00:14:21,120 --> 00:14:23,120 Yeah. There is no particle mediating this force. 154 00:14:23,600 --> 00:14:28,700 So what's it is possible to describe the weak interaction in the framework of this quantum field theory? 155 00:14:29,270 --> 00:14:30,200 And the answer is yes. 156 00:14:30,440 --> 00:14:37,040 And the point is that as opposed to the blue one and the photon, which has no mass, they are massless the carriers of the weak interaction, 157 00:14:37,250 --> 00:14:44,060 which are the WS and their bosses, they have a very massive they have a mass of almost 80 GBPS, so 80 times the proton mass. 158 00:14:44,750 --> 00:14:52,730 Therefore, if you look at weak interactions at low energies, you would never resolve the mass with just a point interaction as once you hear. 159 00:14:53,000 --> 00:14:54,350 But if you go to very high energy, 160 00:14:54,440 --> 00:15:00,500 you will see that actually there is a particle propagating like just like the photon or it, but that is very massive. 161 00:15:00,950 --> 00:15:05,630 So in the standard model, the weak interaction of Fermi can be seen as here. 162 00:15:05,660 --> 00:15:09,320 So we have this ah neutron composed down, up, down. 163 00:15:09,590 --> 00:15:17,360 These are proton composite, right down, up, up. And then the down emits the larger you boson so transforms into an output and it will 164 00:15:17,360 --> 00:15:22,880 give us some indication for the electron unable to do so exactly as s as Fermi had. 165 00:15:23,540 --> 00:15:27,200 But now in the context of that, nobody is able quantum theory. 166 00:15:28,200 --> 00:15:33,930 So also in this in the seventies, the fact that this theory was the right explanation of the interactions was verified. 167 00:15:34,350 --> 00:15:38,340 So, for example, the discovery of neutral currency neutrino scattering. 168 00:15:38,700 --> 00:15:47,460 So you have high energy beams of neutrinos which you point to some target, and then you try to reconstruct the results of this collision. 169 00:15:47,940 --> 00:15:52,919 Now, one of the predictions of this was that the neutrino there would be neutral patterns in the sense 170 00:15:52,920 --> 00:15:58,110 that the neutrino will interact via the neutral particle that and then hadrons would be formed, 171 00:15:58,110 --> 00:16:06,480 but no other charge that happens. So these the neutrino these are the traces of the of the evidence for the collision, but there's no charge at level. 172 00:16:06,750 --> 00:16:13,660 So you have neutral currents. And then you also mentioned that the analysis of this kind of images was done among other places. 173 00:16:13,860 --> 00:16:19,770 Know what we are speaking now, which had a crucial role in the discovery of that of the neutral currents. 174 00:16:21,520 --> 00:16:25,850 So we have seen the electromagnetism, the strong interaction and the weak interaction. 175 00:16:26,050 --> 00:16:29,170 What is the only missing piece? This is the the Higgs mechanism. Right. 176 00:16:29,650 --> 00:16:33,720 So what's the problem? Well, Julia will talk much more about this. 177 00:16:33,740 --> 00:16:41,680 Let me just explain it briefly. So the problem is that in the standard model, its symmetries don't allow to have mass in the Lagrangian. 178 00:16:41,770 --> 00:16:44,470 Right. So in particular, we have a electroweak. 179 00:16:45,370 --> 00:16:53,230 A Electroweak theory has a asymmetry between left handed and right handed particles, which for beat the particles. 180 00:16:54,730 --> 00:17:02,170 So what is the Higgs mechanism? These are very clever trick to bypass the restriction, because in the Higgs mechanism the laws are still symmetric. 181 00:17:02,410 --> 00:17:05,680 But the configuration that nature has chosen is not symmetric. Right. 182 00:17:06,010 --> 00:17:09,130 Is this is the famous Mexican hat potential. 183 00:17:09,280 --> 00:17:12,850 Right. If you look at this potential, this potential exploitation, asymmetric, right. 184 00:17:13,150 --> 00:17:20,720 Any direction looks the same. However, the point where the Higgs field just has to be is not is not traditional 185

00:17:20,770 --> 00:17:25,180 symmetric is just one point of all the possible end points of the of the minima. 186 00:17:25,630 --> 00:17:28,900 So these are spontaneously symmetric breaking that laws asymmetric. 187 00:17:29,230 --> 00:17:32,800 However, the specific configuration of the vacuum is not. 188 00:17:33,720 --> 00:17:38,760 So it's actually a mechanism that all the particles in the standard model can operate en masse. 189 00:17:39,600 --> 00:17:45,180 And it's a crucial product. If the energy of interaction is high enough, we can excite the Higgs field. 190 00:17:45,600 --> 00:17:49,450 And excitations of this Higgs field are the Higgs particle which can be produced. 191 00:17:49,470 --> 00:17:53,010 And that's the ultimate test, that this explanation is the right one, 192 00:17:53,010 --> 00:17:58,800 that the Higgs mechanism is correct description of the mass, and the model is the discovery of the Higgs boson. 193 00:17:59,520 --> 00:18:02,010 So it was predicted more than 50 years ago, 194 00:18:02,220 --> 00:18:08,940 but it took an impressive and impressive effort from theories that experimentalists to be able to develop the calculations 195 00:18:08,940 --> 00:18:14,940 and the machines to be able to finally vindicate this prediction and was discovered two years ago at the Lateran Collider. 196 00:18:16,320 --> 00:18:19,650 Okay. So this is the standard model. Let me move to the second part of my thought. 197 00:18:20,250 --> 00:18:26,160 How can we explore the high energy frontier? And this is the best machine we have nowadays to explore the frontier. 198 00:18:26,700 --> 00:18:28,020 Is there a Large Hadron Collider? 199 00:18:28,920 --> 00:18:34,800 So, first of all, why do we care about high energy colliders, what they are suitable to explore really nature at the smallest possible distances. 200 00:18:35,280 --> 00:18:43,530 But we know from the Heisenberg Principle this is there was a question here that if we want to prove something which very small resolution, 201 00:18:43,860 --> 00:18:46,490 we need to have a proof which is very energetic. Right. 202 00:18:46,860 --> 00:18:55,680 So if we want to resolve an object to very small scale, we with a particle which is very energetic, if not, it will be impossible. 203 00:18:56,130 --> 00:19:00,600 So a rule of thumb is to convert distances in energies is the following. 204 00:19:00,930 --> 00:19:10,440 If I have a particle with one GV, this corresponds to roughly a distance of a .8.42 ten to the minus time into a matter of 50 metres. 205 00:19:10,440 --> 00:19:19,710 It's called 0.2 pendulums. This conversion sets the energy that we need to more or less use to explore smaller and smaller objects. 206 00:19:19,800 --> 00:19:25,710 Like, for example, a an atom has a length of about 10 to -8 centimetres, right? 207 00:19:26,100 --> 00:19:30,750 So we need energy of the earth at about 2.5 million to exploit a structure. 208 00:19:31,990 --> 00:19:37,420 If

we want to prove the structure of an atomic nucleus, this is an object of about ten to the -40 metres. 209 00:19:37,720 --> 00:19:46,090 We energies of the order of 200 amoebae, which makes sense because these are typical energies which are that are relevant for nuclear processes. 210 00:19:46,570 --> 00:19:55,450 If we want to go to even smaller distances in particular to to prove the structure of the proton, we need a particle has energies in the GBE range. 211 00:19:55,870 --> 00:20:02,890 And this was precisely by the experiments in like a ten GB because this is right energy to be able to resolve the internal structure of the proton. 212 00:20:03,460 --> 00:20:09,970 If we want to go further and explore, for example, if electrons or quarks have a further structure, 213 00:20:10,330 --> 00:20:15,700 then we need to prove energies because a quad is known to have our radius of a smaller than 10 to 16 centimetres. 214 00:20:15,970 --> 00:20:23,770 So with energies of of two TB right. So if we want to reach really the smallest possible distances, there is no other option. 215 00:20:23,950 --> 00:20:28,770 But going to that to these wide the LHC collider that is bring the escape. 216 00:20:29,780 --> 00:20:33,200 No high energy carriers have been around for a while. 217 00:20:33,230 --> 00:20:38,210 Right. The first collider was there, the Lawrence cyclotron in Berkeley. 218 00:20:38,810 --> 00:20:44,180 And as you can see, by the standards that we are now used to, it is just, you know, 219 00:20:44,330 --> 00:20:51,210 it's almost at that point, right, is only 1.5 metres and the energy seems very small at 15 maybe. 220 00:20:51,500 --> 00:20:56,660 But this was really crucial, right? Because this was the first time that in a controlled setup, 221 00:20:56,720 --> 00:21:01,850 you could accelerate particles and restore its results without a with without the collider. 222 00:21:01,850 --> 00:21:07,580 What is the problem? And we want to use we can only use cosmic rays, for example, or, or that natural process. 223 00:21:08,120 --> 00:21:11,540 So we cannot control in detail which are the settings of our collision. 224 00:21:11,540 --> 00:21:14,659 And this is of course not good for extend our point of view. 225 00:21:14,660 --> 00:21:22,459 We want to control everything. And in the case of our cyclotron, we have all the activities that we want to to control the energy of the collisions. 226 00:21:22,460 --> 00:21:26,840 And then these are very clean proof of air. Of our experiment. 227 00:21:27,380 --> 00:21:32,210 So they have many other colliders being built. And then I would just highlight three of them. 228 00:21:32,840 --> 00:21:37,760 One of these is it's like this the Stanford Linear Collider with a length of three kilometres. 229 00:21:37,760 --> 00:21:45,530 This is in in California. And an edge of 98 is a linear collider, which means that I collide electrons with positrons. 230 00:21:45,980 --> 00:21:49,610 These are

very clean experiment. However, it switching energies limited. 231 00:21:50,530 --> 00:21:57,459 There's also the collider in Amber, which was the first and only electron proton collider ever built. 232 00:21:57,460 --> 00:22:05,380 So we have a high energy beam of electrons colliding with a high energy team of protons, the length of six kilometres and the energy of 210 GB. 233 00:22:06,390 --> 00:22:12,840 And then there was the platinum collider in Chicago, which was before the energy was the highest energy collider of the world, 234 00:22:13,110 --> 00:22:16,200 which is a proton collider in a tunnel of six kilometres. 235 00:22:16,200 --> 00:22:23,400 And the energy you have out to TV. Each of these experiments has provided us crucial information of the standard model. 236 00:22:23,910 --> 00:22:30,870 But since a some years, some years ago, we have the Large Hadron Collider really and is an impressive machine. 237 00:22:30,870 --> 00:22:34,890 Right? It's the most powerful accelerator ever built by mankind. 238 00:22:35,190 --> 00:22:40,620 They taught it at CERN in Geneva, which is the sun, is the European Laboratory for particle physics. 239 00:22:41,070 --> 00:22:47,190 So it's composed by a massive 27 kilometre long tunnel with four gigantic detectors in them. 240 00:22:47,490 --> 00:22:51,690 So this is the this is a photo taking of the LHC area. 241 00:22:51,720 --> 00:22:56,640 So this is the Geneva Airport for those of you that nobody at the Geneva. 242 00:22:57,450 --> 00:23:01,080 This is where seven is located. So my office used to be here for three years. 243 00:23:01,470 --> 00:23:06,720 And then underneath all this area, there is a Large Hadron Collider. So these are the SPS. 244 00:23:07,020 --> 00:23:11,570 And then this is the LHC tunnel that goes almost from the airport to the lake. 245 00:23:11,580 --> 00:23:14,880 And then today I'm on the other side of the lake. 246 00:23:16,120 --> 00:23:22,209 And identity of the protons attacks had the highest energies ever approved with the goal, 247 00:23:22,210 --> 00:23:27,370 as I was mentioning, to explore the laws of nature, the smallest distances ever achieved. 248 00:23:28,290 --> 00:23:31,950 So in the LHC there are four massive detectors. 249 00:23:32,280 --> 00:23:35,540 They are called Atlas CMS, satellite TB. 250 00:23:36,120 --> 00:23:42,750 You can see, you know, by comparing with the size of a of a of a person, they are really they're really massive. 251 00:23:42,960 --> 00:23:48,030 They are like six, seven, eight story buildings of an amazing technology. 252 00:23:48,540 --> 00:23:53,580 I'm always impressed that these things even managed to work. Right. You have something which is huge as a building. 253 00:23:53,610 --> 00:23:57,899 Everything wires and detectors. And, you know, it manages to work on two quite impressive measurements. 254 00:23:57,900 --> 00:24:01,020 I think that's the technological is an impressive achievement. 255 00:24:01,770 --> 00:24:09,059 So I say, well, I also wanted to mention that Oxford has played the central role both in building 256 00:24:09,060 --> 00:24:13,470 these detectors and now in operating them and extracting the most of that information. 257 00:24:14,250 --> 00:24:16,050 The galaxies are an impressive machine, right? 258 00:24:16,260 --> 00:24:23,440 But without its detectors, which are able to explore, you know, and able to extract information from the collisions, then it would be useless. 259 00:24:23,460 --> 00:24:26,820 So we thought the detector, having very energetic protons, is not very useful. 260 00:24:27,660 --> 00:24:32,610 So let me show how articulation looks like. So these are nice video done by their Atlas collaboration. 261 00:24:33,120 --> 00:24:41,260 So this is the LHC tunnel. Right. So here you have there we have that protons, which are actually a very, very high energies. 262 00:24:42,000 --> 00:24:48,030 Right. So let's go inside the beam. This is the proton composed by in this video by three quarks. 263 00:24:48,540 --> 00:24:51,569 And the proton is six and eight of them. At some point the beams will cross. 264 00:24:51,570 --> 00:24:55,410 Right, and they will cross in the interaction points whether that they are located. 265 00:24:55,680 --> 00:25:00,210 So we have their proton beams, they get close to each other, and then eventually they collide. 266 00:25:01,050 --> 00:25:10,530 And what the detector does is by reconstructing the traces of the collision, reconstructing the hadrons, the leptons, the most, the missing energy, 267 00:25:11,070 --> 00:25:18,690 that the aim is to reconstruct what has happened in this interaction point, because this interaction point is that collision of very high energies. 268 00:25:18,930 --> 00:25:23,400 So therefore, here is precisely what we are calling nature at the smallest distances. 269 00:25:25,470 --> 00:25:29,520 So let me mention some facts about the LHC, which I think are quite interesting. 270 00:25:29,760 --> 00:25:35,930 So first of all, LHC is one of the coldest places in the universe in order to keep it in magnets. 271 00:25:36,060 --> 00:25:42,860 So it is based on semiconductor superconducting magnet in order to keep these magnets operating with very, very low temperatures. 272 00:25:42,900 --> 00:25:51,810 So the LHC will have a 30 kilometres tunnel just kept at only two degrees above absolute zero, which is, you know, it's called the interstellar space. 273 00:25:52,790 --> 00:25:56,270 Another interesting fact is this is one of the empty space in the solar system. 274 00:25:56,450 --> 00:26:03,110 Why? Because if in the beam where we have the problems running, there is even a very small density of air particles. 275 00:26:03,410 --> 00:26:09,200 The problem we've had with these particles and we will not be able to explore the in the detector. 276 00:26:09,500 --> 00:26:13,000 So we with really a very, very high vacuum like us. 277

00:26:13,010 --> 00:26:16,050 Another interesting fact is that it's one of the hottest places in the galaxy. 278 00:26:16,100 --> 00:26:20,840 So, for example, when we collide, heavy ions like for example, that in the LHC, 279 00:26:21,200 --> 00:26:27,019 the temperature that we generate is an example of these collisions are billions of times larger than in the sun. 280 00:26:27,020 --> 00:26:30,920 Right. Which is the conditions similar to those in the very, very early universe. 281 00:26:31,910 --> 00:26:40,790 And also a final score. They think it's really impressive is the amount of information that we extract from the LHC in just one second. 282 00:26:41,120 --> 00:26:45,780 The LHC in principle could record one third of out of data just per second. 283 00:26:45,800 --> 00:26:50,750 Right. So this is like having to record 10,000 sets of Encyclopaedia Britannica per second. 284 00:26:51,410 --> 00:27:00,470 So it is it's an impressive technological challenging to be able to efficiently skim all this huge amount of information for the relevant events. 285 00:27:01,490 --> 00:27:06,590 So what bility has has what have we learned fertility up to now? 286 00:27:07,130 --> 00:27:10,730 So the first result has been that rediscovery of this model. 287 00:27:11,090 --> 00:27:18,320 What do you mean by rediscovery? Well, in the previous slides I mentioned the discovery of the deep sea obsidian as a particle. 288 00:27:18,800 --> 00:27:22,580 The very first thing that DDT had to do is to check that everything was still there. 289 00:27:22,820 --> 00:27:27,260 And this might seem obvious, but it is not because this machine is technologically very complex. 290 00:27:27,260 --> 00:27:32,330 So first of all, we have to validate that everything is in place, that the detectors went to the detectors, its performance. 291 00:27:32,720 --> 00:27:36,590 And also, we need to check out our calculations, which have been tested before at lower identities. 292 00:27:37,160 --> 00:27:41,070 Also hold high energies, because we are these are very largely average. 293 00:27:41,190 --> 00:27:46,640 That's increasing the energies. So the in this book here by this collaboration, this is a plot of the. 294 00:27:47,030 --> 00:27:50,720 This is proton proton collisions into the news in this case. 295 00:27:51,290 --> 00:27:56,240 And each time we see a peak, it means that there is a new particle has been produced in this collision. 296 00:27:56,600 --> 00:27:59,989 So, for example, if we look at around three, three gbps, we see a peak. 297 00:27:59,990 --> 00:28:06,629 This is a site discovered in 73. If we look at above at 1022, we see the epsilon. 298 00:28:06,630 --> 00:28:11,930 This is bottom 90, both the mission discovery in 77 and then at around 100 GB that does have mass, right. 299 00:28:12,260 --> 00:28:14,150 It was very nice to see that no ability. 300 00:28:14,330 --> 00:28:20,210 We can quickly rediscover the oldest under model and test our calculation with a very high degree of accuracy. 301 00:28:20,690 --> 00:28:27,139 And this is very important because predicting the standard as well as just passing predicted processes with 302 00:28:27,140 --> 00:28:31,700 very high accuracy could be the key to discover new physical reality in there in the following years. 303 00:28:33,110 --> 00:28:36,890 Of course, the biggest achievement of the LHC has been the discovery of the Higgs boson. 304 00:28:37,220 --> 00:28:44,040 In this video here, I'm showing a collision in which a Higgs boson candidate is being is being formed into four into four leptons. 305 00:28:44,040 --> 00:28:47,629 So each of these four lines is are four leptons, 306 00:28:47,630 --> 00:28:52,520 which is one of the cleanest channels of the production of the K and Julia know talk about this later. 307 00:28:53,180 --> 00:28:59,750 And this is a extremely challenging measurement, right? Because it requires to disentangle a very small signal from of a large background 308 00:29:00,200 --> 00:29:05,450 and to try to to convey the message of how challenging these measurements are. 309 00:29:05,810 --> 00:29:10,820 Let me show you an extended mission by the Atlas collaboration. So how we discovered the Higgs from the practical point of view. 310 00:29:10,850 --> 00:29:14,630 So we begin without any data, right? And we want to measure two things. 311 00:29:14,990 --> 00:29:19,580 One, to measure the masses of default numbers so the Higgs can decay into pairs of photons. 312 00:29:19,850 --> 00:29:25,130 So if we look at beta photons and compute the mass, if we see a peak, that would be a discovery of the Higgs boson. 313 00:29:25,610 --> 00:29:27,380 The same the Higgs can be came to four letters. 314 00:29:27,650 --> 00:29:33,140 So if I compute the mass of four atom events, which is not in this model, will be evidence for the Higgs. 315 00:29:33,650 --> 00:29:38,390 Right. So let me begin to take data. So slowly I began to accumulate data. 316 00:29:38,540 --> 00:29:44,420 But here there's nothing, just a flat line. So just background. But with more and more data, right? 317 00:29:44,720 --> 00:29:48,440 Something will appear. What will appear? There's a structure forming here, right? 318 00:29:49,100 --> 00:29:52,640 And what is this structure? This is a peak around 25. 319 00:29:52,850 --> 00:29:57,350 TV is very interesting because this is this could be the mass of the Higgs boson. 320 00:29:57,830 --> 00:30:02,000 Now, is it really the Higgs boson could be something as a statistical fluke? 321 00:30:02,090 --> 00:30:07,700 Well, what we do is to go to the other process, which is going to four leptons and also big data here. 322 00:30:07,740 --> 00:30:12,170 Right. So I'm taking data in the Higgs into four letters to begin with. 323 00:30:12,320 --> 00:30:16,940 I don't have anything. So I need to more and more data. Everything looks under model no Higgs. 324 00:30:17,360 --> 00:30:24,110 But

eventually there are some events here that hey, they are their mass 125 GV and they are not they are not. 325 00:30:24,110 --> 00:30:26,390 Some said that for example, this could be a Higgs. 326 00:30:26,810 --> 00:30:34,190 And the crucial thing is that this signal here has a peak at exactly the same mass as they're wanting today for the channel. 327 00:30:34,610 --> 00:30:39,860 These are very strong. Check that this feature here, this feature here correspond to the same logic like this, 328 00:30:39,860 --> 00:30:45,680 that the Higgs boson and actually at the at the LHC, these two channels, two forms, four letters. 329 00:30:45,980 --> 00:30:51,140 What are the ones that we are able to proclaim our discovery in July 2012. 330 00:30:52,050 --> 00:31:00,420 So it really this is why after this massive exercise, we can be happy because we found the Higgs boson. 331 00:31:01,600 --> 00:31:08,860 No. Okay. However. Some of our models is an impressive success and we should be really proud of. 332 00:31:08,860 --> 00:31:11,500 It is one of the greatest success of modern science. 333 00:31:12,070 --> 00:31:19,750 However, despite its successes and discoveries, Higgs boson, there are many crucial questions which are still left open. 334 00:31:20,050 --> 00:31:27,280 For example, the stability of the Higgs Mass. Why the Higgs Mass is what it is and not the mass of the mass at very, very high energies. 335 00:31:28,030 --> 00:31:33,579 What is the nature of dark matter or that cannot see those forces unify into a single one? 336 00:31:33,580 --> 00:31:38,290 So our strong interactions with interactions and explanation aspects of the same force or they are not. 337 00:31:38,830 --> 00:31:43,540 Is there a theory of everything? What is the role of gravity? Because the gravity doesn't fit in a standard model, right? 338 00:31:44,230 --> 00:31:46,209 What is the origin of the matter? Anti-matter asymmetry. 339 00:31:46,210 --> 00:31:50,820 So there are many questions which are really crucial that have been not that are left open by another model. 340 00:31:51,610 --> 00:31:58,629 And the interesting thing is that there are many theories that go beyond the standard model, and many of these can be tested at the LHC. 341 00:31:58,630 --> 00:32:06,220 So the LHC is a unique tool to scrutinise these theories, which will try to attempt some of the limitations of the standard model. 342 00:32:07,000 --> 00:32:11,200 One popular example that you might have heard about is called supersymmetry. 343 00:32:11,590 --> 00:32:19,690 So in supersymmetry, each particle has a super partner. So we have talked about quarks, neutrinos, the force carriers and the Higgs boson. 344 00:32:20,110 --> 00:32:27,190 So in supersymmetry, we have the standard model and we have another copy of all the particles with the spin the force by one half. 345 00:32:27,490 --> 00:32:31,450 So you have the force which had us no fermions anymore. 346 00:32:31,900 --> 00:32:40,150 We have this leptons and then we have the the best symmetric version of the case, Boston Dynamics of the Higgs, which is called the Higgs. 347 00:32:40,870 --> 00:32:43,900 And among all the things that have been predictions of supersymmetry, 348 00:32:44,140 --> 00:32:49,030 it predicts that all the free forces are strong with magnetic, if you will, two very high energies. 349 00:32:49,390 --> 00:32:51,120 They become just a single, single force. 350 00:32:51,130 --> 00:32:57,910 So this what is called a force unification, which is, of course, a very attractive theory out of a fundamental theory of nature. 351 00:32:58,480 --> 00:33:02,740 However, as of today, there are no hints of yes in physics ability. 352 00:33:03,190 --> 00:33:08,620 However, in just a few months, data will have started even higher energies and will have ten, 15, 353 00:33:08,620 --> 00:33:15,040 20 years to keep exploring the high energy frontier and try to understand all these pressing and very important questions. 354 00:33:15,490 --> 00:33:21,370 So I think that it is very likely that we have many new breakthroughs and we are on the corner. 355 00:33:23,050 --> 00:33:26,770 Okay. So in the last 5 minutes, I want to mention what's next, right? 356 00:33:27,310 --> 00:33:33,490 What's what's beyond reality? And this is important because in high energy physics, building these facilities, 357 00:33:34,000 --> 00:33:38,080 since it's really at the cutting edge of technology, it takes long timescales. 358 00:33:38,470 --> 00:33:42,790 Right. Both from the civil engineering to a technology to or to the physics, 359 00:33:43,210 --> 00:33:49,030 say something that even if we are only at the beginning of the LHC problem, we have to begin to think what comes next. 360 00:33:49,930 --> 00:33:53,710 So this is the scale of the LHC for the next 25 years. 361 00:33:54,250 --> 00:33:59,709 So I'll say what's amazing, they deliver a huge amount of interesting results, but we are just at the very beginning of the problem. 362 00:33:59,710 --> 00:34:07,810 Right. So we have seen how they can data for three years at seven TV and a TV reality has some that are going along shut down of two years. 363 00:34:08,050 --> 00:34:15,490 And now we are here. We are about at the beginning of day, which is called rental, where the energy has increased from eight TV from 13 to 14 TV. 364 00:34:16,240 --> 00:34:22,330 So there will be a period of about eight years of running for TV and then there will 365 00:34:22,330 --> 00:34:26,709 be a very important upgrade in which the LHC will be turned into the high luminosity. 366 00:34:26,710 --> 00:34:28,390 LHC What's a high luminosity? 367 00:34:28,460 --> 00:34:36,370 It's only the number of collisions per bunch crossing will be increased substantially, so increasing the chances of finding interesting events. 368 00:34:37,690 --> 00:34:42,610 So we have half work for the next 20 years to really try to explore the high

energy frontier. 369 00:34:42,850 --> 00:34:50,950 And the LHC is the best machine that we have for this. And something which is crucial, especially in the lack of any evident signal of BFM theory, 370 00:34:51,400 --> 00:34:59,410 is to try to sharpen our understanding of the weak interactions, electromagnetism, because this would be the key of new discoveries. 371 00:34:59,680 --> 00:35:03,250 New discoveries would appear as a subtle deviation from some normal prediction. 372 00:35:03,520 --> 00:35:09,010 So the better you can compute things with high precision, the closer could be to a new discovery. 373 00:35:09,310 --> 00:35:14,590 At the Large Hadron Collider. And of course, it's essential to have a very close interplay between theory and experiment. 374 00:35:14,590 --> 00:35:20,520 Right. And two of the central ingredients of the LHC program for the next 20 years. 375 00:35:20,730 --> 00:35:25,860 Well, first of all, precision measurements of the Higgs couplings. And Julia will talk about this in her talk. 376 00:35:26,280 --> 00:35:31,140 And then the search for dark matter. The LHC and Woolly again will tell us about this. 377 00:35:32,570 --> 00:35:39,890 So as I was saying in about 2022, we have to upgrade the LHC and turn it into our high luminosity machine. 378 00:35:40,550 --> 00:35:45,330 What's the high luminosity, as it was mentioning, is now in the municipality. 379 00:35:45,380 --> 00:35:52,040 The number of collisions that a bunch of crossing would be much higher, which means that the chances of finding interesting events will be larger. 380 00:35:52,490 --> 00:35:57,770 Of course this has challenges because if you have more collisions, you have more single events, 381 00:35:58,130 --> 00:36:02,150 but also many more background events like these because this looks extremely messy. 382 00:36:02,390 --> 00:36:10,460 We have to extract interesting signal in a in a collision where we have almost 200 collisions, literally a background noise and need to be removed. 383 00:36:11,090 --> 00:36:15,910 So this requires a complete upgrade of the LHC detector. 384 00:36:16,370 --> 00:36:23,090 And also here, Oxford is studying a central role, in particular in the case of Atlas in building the new Atlas Atlas Silicon Tracker. 385 00:36:24,410 --> 00:36:28,820 And so let's try to think even bigger. So what comes in the next 20, 30 years? 386 00:36:29,240 --> 00:36:34,310 Well, as I was mentioning, the planning of these facilities is always an expression of very long timescale. 387 00:36:34,400 --> 00:36:38,750 Right. Because we are at the cutting edge of technology, of civil engineering. 388 00:36:38,960 --> 00:36:42,830 You know, there are problems that these machines are planning the solution. 389 00:36:43,480 --> 00:36:51,100 So we to think we are out of time. So in particular now we are discussing whether the next peak machine would be 100 TV. 390 00:36:51,100 --> 00:36:54,400 Collider So seven times higher than the Large Hadron Collider. 391 00:36:54,880 --> 00:37:03,910 Also, we have electron positron, an electron proton model. This is called tentatively Future Collider and this is the plan of a possible site. 392 00:37:03,910 --> 00:37:07,990 This would be again in Geneva. So is the LHC tunnel. 393 00:37:08,350 --> 00:37:12,430 This would be the 100 kilometre long tunnel where this could be built. 394 00:37:12,540 --> 00:37:19,870 So you see that it's quite impressive that as compared to the FCC, it's very small, despite being an incredibly large machine. 395 00:37:20,590 --> 00:37:26,230 Also sites China is very interested in this kind of projects. And there's a proposal for the FCC in China. 396 00:37:26,860 --> 00:37:29,290 And now in the context of of working groups, 397 00:37:29,290 --> 00:37:35,800 there is a worldwide effort trying to understand both the technical feasibility and the physics motivation of this of this proposal. 398 00:37:36,400 --> 00:37:39,670 There are also other ways that we could explore the hydrogen from the earth. 399 00:37:39,670 --> 00:37:45,940 For example, there are plans to build a linear collider where you have electrons and positron collisions at very high energies. 400 00:37:45,940 --> 00:37:49,030 For example, there is the plan of having click in Geneva. 401 00:37:49,120 --> 00:37:59,050 It would be a linear, linear tunnel that goes from the French part of the French area to almost all given crossing all the Geneva area. 402 00:37:59,680 --> 00:38:04,540 These are cleaner machines because electrons are fundamental constituents, so there is less background noise. 403 00:38:04,870 --> 00:38:08,110 However, they have greatly reduced reduce friction. 404 00:38:08,970 --> 00:38:15,550 In. So I think that I've tried to convey that this is really a fascinating time to be in particle physics, 405 00:38:16,060 --> 00:38:21,459 that this has been an incredibly successful theory and that it will be the 406 00:38:21,460 --> 00:38:25,810 best tool we have to explore the high energy frontier for the next 20 years. 407 00:38:25,810 --> 00:38:29,590 I think that you should really stay tuned for news for the LHC because I'm sure that 408 00:38:29,590 --> 00:38:33,600 there will be very interesting results from us and you will be happy to have them about. 409 00:38:33,710 --> 00:38:35,290 So thanks for your attention.