1 00:00:02,440 --> 00:00:11,780 Don't have any. OK, thank you. 2 00:00:11,780 --> 00:00:16,010 Everyone can hear me. Sounds like I can hear myself, which is a good start. 3 00:00:16,010 --> 00:00:22,580 OK, so yes, as you've just heard, I'm going to be breaking down a little bit more in a little bit more detail. 4 00:00:22,580 --> 00:00:32,270 If you like how we know what we're doing, see how we can use those protons to tell us about the Higgs and all the other exciting things we're doing. 5 00:00:32,270 --> 00:00:38,010 So indeed, we've heard we've heard from Gavin about the Large Hadron Collider at about. 6 00:00:38,010 --> 00:00:45,190 You know what it can do, what the physics it can probe, and we know we saw in that animation, what's it doing? 7 00:00:45,190 --> 00:00:54,390 Well, it's it's getting protons, it's accelerating them to high energies, essentially smashing them together and seeing what happens. 8 00:00:54,390 --> 00:00:57,120 So, you know, there's a lot in that kind of sentence, I suppose, you know, 9 00:00:57,120 --> 00:01:03,180 how do you go from smashing something together to seeing what happens to understanding things about the Higgs boson? 10 00:01:03,180 --> 00:01:08,100 And it's, you know, it's it's not a trivial thing, and it's there's a lot of interesting physics in that. 11 00:01:08,100 --> 00:01:14,220 So we're colliding protons, but we know protons themselves a composite complex, objects made of quarks. 12 00:01:14,220 --> 00:01:19,130 And so the question is, what is a proton? I told you half the answer, but there's more to it than that. 13 00:01:19,130 --> 00:01:27,620 And crucially, actually, how does it behave when we give it the LHC treatment and really speed these things up and we collide them head on? 14 00:01:27,620 --> 00:01:35,270 So that's what I'll talk about first from a fairly briefly from a historical point of view, kind of telling you what the proton is. 15 00:01:35,270 --> 00:01:41,390 I'm sure you'll know some of it, but probably not all of it. And then going going on to here. 16 00:01:41,390 --> 00:01:48,560 So here is the roadmap. And it's worth remembering that over the past century, we really have come a long way in understanding, 17 00:01:48,560 --> 00:01:53,510 well, festival, all discovering a proton and then actually understanding what it is. 18 00:01:53,510 --> 00:01:56,730 And it's really a story that's continuing today. 19 00:01:56,730 --> 00:02:03,590 Well, basically uncovering layers and layers of deeper complexity and substructure, complexity and simplicity, 20 00:02:03,590 --> 00:02:08,960 if you like, but certainly substructure things going on at smaller and smaller, distant scales. 21 00:02:08,960 --> 00:02:13,430 So we start with Rutherford's on the discovery of what the nucleus? 22 00:02:13,430 --> 00:02:19,700 And then we know that that is then made of protons, and then we find out what actually, the proton is not a fundamental object. 23 00:02:19,700 --> 00:02:26,390 It's made of corks, and these things interact via quantum chromate dynamics and building on all of that understanding. 24 00:02:26,390 --> 00:02:28,670 Here we are today, and we're really using these things. 25 00:02:28,670 --> 00:02:36,820 This complex mass, if you like here as a precision discovery tool and a precision tool to actually probe the Higgs boson. 26 00:02:36,820 --> 00:02:41,800 So, yeah, how do we do that? Well, let's start at the beginning. 27 00:02:41,800 --> 00:02:49,660 And remember, you know, start the 20th century, we didn't really know what an atom was, let alone a proton. 28 00:02:49,660 --> 00:02:54,730 You know, atomic theory was well established, but we didn't really know what this thing was. We knew there were things called electrons. 29 00:02:54,730 --> 00:02:59,020 We knew there was some rough kind of size 10 to the minus 10 metres. 30 00:02:59,020 --> 00:03:02,770 We knew that they were neutral and therefore that had to be something with positive electric charge. 31 00:03:02,770 --> 00:03:10,990 But potentially it could just be some typical plum pudding like picture a big cloud of positive charge with the electrons dotted in amongst it. 32 00:03:10,990 --> 00:03:15,910 How do we go further than that? What we need to look to look inside the atom? 33 00:03:15,910 --> 00:03:21,130 Not in order, not, you know. How do you look inside something that's that small is not obvious. 34 00:03:21,130 --> 00:03:28,120 And the answer is, well, rather like, you know, I look at our desk photons from the beam photons coming from the Sun. 35 00:03:28,120 --> 00:03:32,980 If you like from the lights, they scatter off the desk, they go into the detector, which is my eye. 36 00:03:32,980 --> 00:03:38,380 And I see that as a desk that is not so different from that, just a very much higher energies. 37 00:03:38,380 --> 00:03:44,800 So Rutherford's, he collided, positively charged alpha particles, helium nuclei with a gold foil. 38 00:03:44,800 --> 00:03:51,460 And he looked at what happens. And that's the basic idea basically on a tabletop in a basement 100 years ago. 39 00:03:51,460 --> 00:03:56,830 So it's basically the fundamentally the same thing we're doing today, colliding things with seeing how they scatter. 40 00:03:56,830 --> 00:04:01,160 We're seeing how to interact. We're seeing what that tells us. 41 00:04:01,160 --> 00:04:06,330 So, of course, he found out that these alpha particles tended to scatter sometimes at rather large angles, 42 00:04:06,330 --> 00:04:13,340 and that was something you couldn't understand from having a diffuse cloud. Rather, that had to be a compact nucleus with a positive charge. 43 00:04:13,340 --> 00:04:17,240 So the alpha particle came in and got to flight and got deflected off. 44 00:04:17,240 --> 00:04:21,530 And you know, it wasn't just a statement of that sort, it was a quantitative statement. 45 00:04:21,530 --> 00:04:26,750 You can predict here, you know, there will be a few equations, but not too many, I promise. 46 00:04:26,750 --> 00:04:31,040 But you can predict how many alpha particles are scattered. 47 00:04:31,040 --> 00:04:36,810 Some give an angle just from the kind of cool on repulsion from that nucleus. 48 00:04:36,810 --> 00:04:43,170 And indeed, it exactly matched that formula, so a point like nucleus with positive charge. 49 00:04:43,170 --> 00:04:47,250 So in what sense was it point like, I mean, how can you ever say anything's point like? 50 00:04:47,250 --> 00:04:51,820 Well, you know, we can never really say is at its point, like within the resolution of the experiment. 51 00:04:51,820 --> 00:04:54,930 So it's smaller than whatever distance scale you can probe. 52 00:04:54,930 --> 00:05:01,890 Distance scale here rather straightforwardly was essentially how close the alpha particle could get to whatever this thing was. 53 00:05:01,890 --> 00:05:08,670 This nucleus was under the Coulomb repulsion that was about 30 metres very small compared to 54 00:05:08,670 --> 00:05:14,100 the atom radius somewhat larger than it turns out Inupiat to be the one the proton size to be, 55 00:05:14,100 --> 00:05:24,300 which is about one centimetre, as I'll discuss. It's a little bit more about that, just breaking it down a little bit more. 56 00:05:24,300 --> 00:05:28,230 If we want to go further, we know Proton exists, we know it's rather small. 57 00:05:28,230 --> 00:05:31,210 But is it point like, does it have an extent? What's it made of? 58 00:05:31,210 --> 00:05:38,550 And the idea is to look deeper and deeper inside the proton to get to higher and higher energy particles and electrons, for example of this thing. 59 00:05:38,550 --> 00:05:41,460 And again, just to see what happens. 60 00:05:41,460 --> 00:05:49,950 And the basic idea is, if you imagine an electron scattering off the proton blob here, it will interact by photon exchange, as we've heard. 61 00:05:49,950 --> 00:05:54,290 And that photon will have a characteristic wavelength. 62 00:05:54,290 --> 00:06:01,050 Losing I and using your kind of classic plank formula relating the energy of that photon to its frequency, 63 00:06:01,050 --> 00:06:06,510 you can get the wavelength of that photon, which gives you the resolution scale in terms of its energy. 64 00:06:06,510 --> 00:06:12,500 And the crucial point here is that the higher energy, the smaller the resolution. 65 00:06:12,500 --> 00:06:20,690 And so we can plug in some rough numbers if we want to plug, if we want to probe a distance scale of one centimetre, that's 10 to the minus 50 metres. 66 00:06:20,690 --> 00:06:28,110 That is, as it turns out, about the size of the proton. You need an energy for that electron of about one GV. 67 00:06:28,110 --> 00:06:33,290 Remember, now this is this energy unit, if you compare to the energies of the protons, 68 00:06:33,290 --> 00:06:38,250 the LHC, the seven thousand, these doesn't seem like much, but in the fifties. 69 00:06:38,250 --> 00:06:43,550 Yeah, I can assure you it was quite the kind of technology then to get to that energy. 70 00:06:43,550 --> 00:06:51,320 And so we build up, we collide Hofstetter, he collides an electron beam with about half a G.V. with protons. 71 00:06:51,320 --> 00:06:56,320 We only have the technology ready status in the fifties. And you see what happens again. 72 00:06:56,320 --> 00:07:01,390 So we have this rather old looking plot, but you know, there's a lot of very interesting physics hidden within it. 73 00:07:01,390 --> 00:07:07,010 So we have the number of scattered electrons again against the scattering angle. 74 00:07:07,010 --> 00:07:12,110 And what you have is a prediction here, which is just that Rutherford prediction, 75 00:07:12,110 --> 00:07:20,330 what would happen if the Proton continued to be point like down to the distance scales you're now probing? 76 00:07:20,330 --> 00:07:24,410 That's the prediction as the data. Completely different. 77 00:07:24,410 --> 00:07:28,520 So it's not certainly not scattering of something point like these distant scales, 78 00:07:28,520 --> 00:07:37,020 and you very much can interpret that as it being actually an extended object, and you can even be more quantitative and get a distance scale out. 79 00:07:37,020 --> 00:07:43,230 So we've got an extended object, it's not like the electrons, it's not like as far as we know, it's obviously made of something. 80 00:07:43,230 --> 00:07:49,050 What is that something? Is it a cloud of some stuff, you know, continuous material? 81 00:07:49,050 --> 00:07:51,960 Is it made of something more fundamental? Well, who knows. 82 00:07:51,960 --> 00:07:57,660 The only way you can answer that question is by looking deeper, going to smaller, distant scales. 83 00:07:57,660 --> 00:08:04,950 And so we come forward to the 70s and the Stanford linear electron collider in California because it's known. 84 00:08:04,950 --> 00:08:13,550 And again, we're colliding electrons with protons. But now at about 40 times higher energy than our original experiment by Hofstetter. 85 00:08:13,550 --> 00:08:14,540 And we look at the same things, 86 00:08:14,540 --> 00:08:19,700 so the electron will scatter off the proton and now the energies are so high that actually it tends to break up that proton, 87 00:08:19,700 --> 00:08:25,400 it tends to tends to destroy it into other particles and you're really seeing inside the proton itself. 88 00:08:25,400 --> 00:08:35,030 And now something slightly at the time, incredibly unexpected and very strange happens, which is that as you go to those smaller, 89 00:08:35,030 --> 00:08:42,740 distant scales, you see a scattering that again looks like the scattering exactly as you'd expect from point like particles. 90 00:08:42,740 --> 00:08:47,510 So this is the plot. This is what it's showing. It's showing a so-called cross section. That's just the rate that the electrons are scattered. 91 00:08:47,510 --> 00:08:55,640 How much are they scatter that each angle and you divide it by the prediction that rather point my prediction? 92 00:08:55,640 --> 00:09:03,080 That is what it would look like. If the proton is a diffuse cloud down to those distance scales, you get less than less scattering. 93 00:09:03,080 --> 00:09:09,710 This is what it looks like, basically flat. Basically, you can understand that point like scattering literally. 94 00:09:09,710 --> 00:09:12,530 By looking at these things, you can see the inside the proton. 95 00:09:12,530 --> 00:09:20,390 There must be some point like objects that electrically charged that we're actually scattering. 96 00:09:20,390 --> 00:09:24,980 So, you know, that's the really compelling evidence that there's something inside the pro-tem. 97 00:09:24,980 --> 00:09:27,680 Of course, there is much other besides, 98 00:09:27,680 --> 00:09:35,450 we knew in the 60s and in the 50s and in the seventies that lots and lots and lots of new particles are being produced in cosmic rays. 99 00:09:35,450 --> 00:09:43,400 We were seeing them in colliders. You couldn't list them all pions on lambdas size, so on and so forth. 100 00:09:43,400 --> 00:09:47,450 And it was completely unexpected. How do you understand this, that these all fundamental? What are they? 101 00:09:47,450 --> 00:09:53,540 How do they interact? And of course, someone had the bright. This cried out an explanation and and showed off. 102 00:09:53,540 --> 00:09:57,290 It had one, which is the from a spectroscopy point of view, 103 00:09:57,290 --> 00:10:03,950 you can understand every single one of these has been a combination of some more fundamental object, which we called a cork. 104 00:10:03,950 --> 00:10:11,840 So fine, you know, did these things exist? Are they just a mathematical object used to describe these things? 105 00:10:11,840 --> 00:10:14,300 Well, people were asking those questions at the time, 106 00:10:14,300 --> 00:10:20,510 but that certainly stopped with a slack experiment to really see that you could actually measure these things and scatter off them. 107 00:10:20,510 --> 00:10:24,410 They were really that forming a proton and the neutron, as we heard. 108 00:10:24,410 --> 00:10:30,600 And we got through three types at a time up, down and strange and more recently, the charm bottom and top. 109 00:10:30,600 --> 00:10:37,200 So we heard from Gavin again, so I won't go through this in detail, but just to reemphasize because it will come up, of course, 110 00:10:37,200 --> 00:10:46,470 as I go on into into and discuss more that the proton is made, it three cooks in the most basic picture to up and down. 111 00:10:46,470 --> 00:10:51,630 These are fractional electric charge. And sure enough, gives us a charge with one proton. 112 00:10:51,630 --> 00:10:57,870 OK, very good. That's that's a that's a kind of cartoon, if you like. But of course, a cartoon only gets you so far. 113 00:10:57,870 --> 00:11:02,130 And there are a lot of questions behind, you know, what is the force behind in these together? 114 00:11:02,130 --> 00:11:12,100 And even if we can put a name to it? How do we actually? Well, we calculate with it, how do we understand what it is and make predictions with? 115 00:11:12,100 --> 00:11:17,230 And this is how we do it. We do it with theory called quantum chromite dynamics. 116 00:11:17,230 --> 00:11:21,190 We heard about quantum field theories in about quantum electrodynamics, 117 00:11:21,190 --> 00:11:26,050 electrons scattering off each other, exchanging other force carrying particles. 118 00:11:26,050 --> 00:11:34,210 Very powerful idea. And the discovery of quarks allowed us to build on that and understand what was binding these things together. 119 00:11:34,210 --> 00:11:36,220 As such, it's such a theory. 120 00:11:36,220 --> 00:11:45,430 So we knew there was a strong force binding the nuclei together because that the proton charge would essentially repel, repel them. 121 00:11:45,430 --> 00:11:48,400 We knew it had to be rather strong, so we called it strong nuclear force. 122 00:11:48,400 --> 00:11:54,850 But until we really uncovered these quarks, this fundamental, apparently fundamental point nine objects within the proton, 123 00:11:54,850 --> 00:11:58,670 we couldn't come up with a convincing theory of the strong force. 124 00:11:58,670 --> 00:12:09,630 But once you had that, you had a fundamental matter particle being the cork, and you could understand it very clearly in terms of that sort of theory. 125 00:12:09,630 --> 00:12:16,320 OK, so that gets us up more or less where we where we where we want to be the LHC. 126 00:12:16,320 --> 00:12:20,010 And so for the rest of the talk, I'll tell you a little bit about actually what we do with the LHC, 127 00:12:20,010 --> 00:12:26,260 with protons and how we can really understand at all what we're doing with them. 128 00:12:26,260 --> 00:12:32,620 So, OK, that's the basic cartoon. Number one, how do we apply that cartoon to the to the LHC? 129 00:12:32,620 --> 00:12:38,170 How do we make predictions? Is there more going on in the proton than that cartoon? 130 00:12:38,170 --> 00:12:42,980 It might be relevant. The Higgs production. The answer is certain yes. 131 00:12:42,980 --> 00:12:51,140 So just to try and give you some idea at a kind of very semi quantitative level about how we understand this. 132 00:12:51,140 --> 00:13:00,950 I'll stick for now with this idea of colliding the electron of a proton and build up a picture of proton and the basic idea as suggested by 133 00:13:00,950 --> 00:13:09,750 that that initial slack experiment was that you don't want to talk about electron proton collisions or proton proton collisions at the LHC. 134 00:13:09,750 --> 00:13:17,690 We want to talk about what you can talk about is rather the collisions of the more fundamental things within the protons and the quarks and gluons. 135 00:13:17,690 --> 00:13:22,310 So that's why we're going. That allows you to make these predictions, but it's not sensible. 136 00:13:22,310 --> 00:13:27,290 I mean, you know, this is a complicated object of corks bound together. 137 00:13:27,290 --> 00:13:34,770 Can you really ignore that fact when you when you in fact ignore that fact, when you when you collide them? 138 00:13:34,770 --> 00:13:38,760 And yeah, the answer is yes, the answer is yes. 139 00:13:38,760 --> 00:13:45,510 And I know there are different ways to get at this, but essentially, in fact, relativity comes to the rescue. 140 00:13:45,510 --> 00:13:52,210 Know there is Einstein looking very happy about that fact. 141 00:13:52,210 --> 00:13:58,570 Very happy indeed, in fact, yeah, it was either that or the one with him sticking his tongue out, so. 142 00:13:58,570 --> 00:14:05,550 Yeah, so right. Think about Proton at rest in Amoco and. 143 00:14:05,550 --> 00:14:09,180 How would that look? It's going to be a dynamic object. 144 00:14:09,180 --> 00:14:13,770 You can have corks, they're going to be interacting, they're going to be moving with a relative motion. 145 00:14:13,770 --> 00:14:19,050 It's going to be a very complicated thing. And now you want to scatter an electron off that and ignore all of that. 146 00:14:19,050 --> 00:14:22,320 And just imagine it just being this, this scatter here. Can you do that? 147 00:14:22,320 --> 00:14:28,200 Do you not need to worry about the kind of coupling all that motion and that interaction with the scatter? 148 00:14:28,200 --> 00:14:35,340 And the answer is you don't. And the reason for that is that, yes, arrest this thing is moving, moving rather fast. 149 00:14:35,340 --> 00:14:45,690 The timescale for these things is that again, not 10 to the minus 24 seconds, a million billion billionth of a second. 150 00:14:45,690 --> 00:14:53,190 Very fast. But nonetheless, there is a time scale associated with it and how you speed these things up to close to the speed of light. 151 00:14:53,190 --> 00:15:00,430 And we have time dilation. Imagine giving the electrons rest, frame a proton rushing towards you at the speed of light. 152 00:15:00,430 --> 00:15:05,530 The clock on that proton coming towards you is going to be moving much slower than the clock at rest, 153 00:15:05,530 --> 00:15:09,760 so that motion or that interaction starts to slow down. 154 00:15:09,760 --> 00:15:15,100 And then it turns out that when you think about that and you think about the time scale that you're actually interacting with this proton wave, 155 00:15:15,100 --> 00:15:18,490 which are called T, cue that it is a lot, 156 00:15:18,490 --> 00:15:22,030 lot less than the time scale that these things are moving around when you think about 157 00:15:22,030 --> 00:15:25,420 that relativistic collision and therefore you're really just seeing a snapshot, 158 00:15:25,420 --> 00:15:32,410 a static snapshot, if you like, of the underlying motion and interaction and you don't need to worry about it. 159 00:15:32,410 --> 00:15:37,750 So as I say, the electron cork interaction time is less than that timescale. 160 00:15:37,750 --> 00:15:44,350 And so it does make sense to talk about an electron scattering more fundamentally. 161 00:15:44,350 --> 00:15:49,900 But is there more to it than that? I mean, clearly I've tried to motivate that there is this static snapshot. 162 00:15:49,900 --> 00:15:55,030 But of course, if you want to understand the scattering, you need to know what that snapshot is of the proton. 163 00:15:55,030 --> 00:16:02,560 What's the underlying prediction for it? What's the underlying distribution for it, if you like? 164 00:16:02,560 --> 00:16:06,230 And again, a little bit of maths, but I will explain it with some cartoons as I go on. 165 00:16:06,230 --> 00:16:13,930 So don't worry too much about that, but you can read everything the relevant variable when you've got two very high energy particles 166 00:16:13,930 --> 00:16:19,510 coming in and colliding is really just how much energy of the cork is the cork carrying, 167 00:16:19,510 --> 00:16:26,080 how much kinetic energy, how much momentum, if you like relative to the total momentum, the total energy of the proton. 168 00:16:26,080 --> 00:16:30,310 And it can even carry all of it, in which Case X would be one where it can carry none of it. 169 00:16:30,310 --> 00:16:36,100 Which case act would be zero? But that's let's break that down a little bit more with some cartoons. 170 00:16:36,100 --> 00:16:36,970 Here was my cartoon. 171 00:16:36,970 --> 00:16:44,680 Here comes an electron scattering off the most basic picture of a proton, and it will scatter off the upper cork site within the proton. 172 00:16:44,680 --> 00:16:47,440 And there is this there is a snapshot. You're not seeing all that motion. 173 00:16:47,440 --> 00:16:54,390 The Electron doesn't see or likely to see something frozen in time comes in and it whacks the book. 174 00:16:54,390 --> 00:17:02,340 Now you do another collision and say what I saw, I'm sorry, what I've shown here is very schematically how much energy is that that caught carrying? 175 00:17:02,340 --> 00:17:08,770 So if you go to the ultraviolet colour coding a lot of energy and you go towards the red carrying less energy. 176 00:17:08,770 --> 00:17:13,000 And you do another collision and it looks different again. You do another collision. 177 00:17:13,000 --> 00:17:20,080 It looks different again. And each time it looks different and you see lots of collisions go back and forward only four of them. 178 00:17:20,080 --> 00:17:26,920 So I have to go backwards and forwards. And you can easily visualise that, OK? 179 00:17:26,920 --> 00:17:28,540 This is quantum mechanics we don't know. 180 00:17:28,540 --> 00:17:35,410 We can never predict that it's going to look like this every time, but that will be an underlying probability, an underlying statistical distribution. 181 00:17:35,410 --> 00:17:42,520 It will look, it will. These will carry more, less energy, a certain amount of time and more energy and other amount of time. 182 00:17:42,520 --> 00:17:52,130 And that will have a distribution. And this is the thing we call a part on distribution function. 183 00:17:52,130 --> 00:18:00,560 They worry too much about the jargon. It's called a PDF, which is not to be confused with a portable document format. 184 00:18:00,560 --> 00:18:08,990 In fact, there is a there is a, I believe, a group that calculates these things in nuclear collisions called EPS. 185 00:18:08,990 --> 00:18:13,370 So it's rather nice joke about encapsulated poster. 186 00:18:13,370 --> 00:18:19,250 But anyway, so yes, that's what we call them. 187 00:18:19,250 --> 00:18:23,660 But forget about the name, really, but I will use it as a shorthand PDF. 188 00:18:23,660 --> 00:18:33,120 It's just this statistical probability distribution. Anushka, you ask, well, how do we how do we measure this, how do we map this out? 189 00:18:33,120 --> 00:18:38,690 And the answer is actually rather rather straightforwardly, at least in the most basic approximation. 190 00:18:38,690 --> 00:18:42,380 And it turns out that if you measure the energy of that scattered electron as it comes out 191 00:18:42,380 --> 00:18:46,850 and you measure the angle that it scatters from just from the kinematics of what's going on, 192 00:18:46,850 --> 00:18:53,000 that it's directly related to how much, how much x how much energy that quote carries. 193 00:18:53,000 --> 00:18:58,730 So we've got to do is we've got to do is build a giant experiment, collide that comes to very high energy. 194 00:18:58,730 --> 00:19:05,390 Then all you've got to do is measure how many times the electron scatter with a certain energy at a certain angle, 195 00:19:05,390 --> 00:19:11,220 and it will be directly related to the underlying distribution. OK. 196 00:19:11,220 --> 00:19:18,300 So so far, so good, but actually not not too relevant to it turns out to what we're doing with the Higgs. 197 00:19:18,300 --> 00:19:24,630 So you need to add the more interesting layers of complication and physics onto what's actually happening in the proton. 198 00:19:24,630 --> 00:19:28,410 So the first step along that is the Proton C satellites. 199 00:19:28,410 --> 00:19:34,170 I have only considered the case of electron scattering scattering off these three that you used. 200 00:19:34,170 --> 00:19:38,220 Because the valence corks within the proton, is that the whole story? 201 00:19:38,220 --> 00:19:45,030 No, certainly not. We know we have Heisenberg's uncertainty principle, something can happen. 202 00:19:45,030 --> 00:19:48,420 Energy, momentum conservation can be violated, 203 00:19:48,420 --> 00:19:55,870 provided it's essentially on a time scale which is sufficiently short enough as set by the uncertainty principle. 204 00:19:55,870 --> 00:20:01,060 And what that means is that in that very strong field of clones, 205 00:20:01,060 --> 00:20:08,200 hawk and anticorpos can pop in and out of existence from that, provided they're only on a very short time scale. 206 00:20:08,200 --> 00:20:13,090 Mathematically, that's how that's expressed. That's the rest mass energy of a cork and an anti cork. 207 00:20:13,090 --> 00:20:17,260 And that is the time scale happened to be sufficiently small. 208 00:20:17,260 --> 00:20:21,760 And you will have heard about that same idea, perhaps people tell you that the vacuum is not a vacuum, 209 00:20:21,760 --> 00:20:26,680 it's full of particles popping in and out of existence. This is rather a similar thing. 210 00:20:26,680 --> 00:20:32,230 Of course, that seems rather indirect. Can we really interact with that while we can? 211 00:20:32,230 --> 00:20:35,470 And here's the very nice idea I told you about the fact that all that motion and those 212 00:20:35,470 --> 00:20:41,200 interactions between the kooks in the basic picture was rather frozen in a snapshot, 213 00:20:41,200 --> 00:20:44,140 and you could scatter off the most centrally instantaneously. 214 00:20:44,140 --> 00:20:47,920 Well, the same is true for all of these cool country corks popping in and out of existence. 215 00:20:47,920 --> 00:20:52,690 So you really, if you can think about it as having a frozen snapshot of all of these cool consequent pairs, 216 00:20:52,690 --> 00:21:00,040 which just so happen to be popping into existence as you scatter off and therefore you can actually interact with them. 217 00:21:00,040 --> 00:21:07,900 So you can't just scatter off the you that basic picture, you can scatter off this whole sea of corks and antiques, and you can measure that. 218 00:21:07,900 --> 00:21:15,620 And once again, you know, the antique walks in the sea can carry different amounts of momentum and you can build up a picture. 219 00:21:15,620 --> 00:21:23,030 So again, the mathematics of this is not too important, what I want to say is that the electron positive electron proton scattering rate can be 220 00:21:23,030 --> 00:21:27,080 written as something due to if you like the scattering rate from those valence quarks, 221 00:21:27,080 --> 00:21:33,770 but also from all of these squawks and anticorpos as well. And you need to include that. 222 00:21:33,770 --> 00:21:43,040 Now we get on to where we really want to go for the Hicks, in fact, which is that I talked about a kind of is this strong glue on it failed again. 223 00:21:43,040 --> 00:21:47,390 Lots of think of lots of balloons being exchanged between all of these courts and so on and so forth. 224 00:21:47,390 --> 00:21:50,930 Very complicated. Get a frozen snapshot of that. 225 00:21:50,930 --> 00:21:58,550 And it turns out you can just as well scatter off those glue ons within the programme so you can imagine a on carrying some amount of momentum. 226 00:21:58,550 --> 00:22:09,320 Scatter off it with a photon, producing a very high energy quote can't quote back flap the proton and again, scatter scatter. 227 00:22:09,320 --> 00:22:17,760 And this has an underlying distribution that you can you can predict or adversary that you can measure. 228 00:22:17,760 --> 00:22:23,850 Right, and there we are. And we're onto the LHC. How does it picture change? 229 00:22:23,850 --> 00:22:28,810 Well, luckily for me and perhaps for you, because otherwise I'd be here for another half an hour. 230 00:22:28,810 --> 00:22:33,060 But the picture doesn't change very much at all at the LHC. 231 00:22:33,060 --> 00:22:37,590 So we're not colliding electrons and protons. Of course, we're colliding protons and protons dominantly. 232 00:22:37,590 --> 00:22:44,670 But the idea is the same. So if you imagine this sort of cartoon of colliding two protons or you've just got an underlying collision 233 00:22:44,670 --> 00:22:48,720 between those that both snapshots again and you just have an underlying collision between them, 234 00:22:48,720 --> 00:22:54,170 the corks or the glue on the corks and the anti quarks within within those protons. 235 00:22:54,170 --> 00:23:01,650 So a simple example is the so-called rally and process. Those are just two physicists who came up with this idea and anti-cult from one 236 00:23:01,650 --> 00:23:08,550 proton from one proton could annihilate an empty coke from another proton. 237 00:23:08,550 --> 00:23:12,810 Produce a virtual photon, which is just an existence for a very short period of time. 238 00:23:12,810 --> 00:23:18,960 And out of measure, let's say, an electron and a positron. And here is the Feynman diagram. 239 00:23:18,960 --> 00:23:23,250 Here is my cartoon equivalent. And that's really what you're interested in. 240 00:23:23,250 --> 00:23:30,900 If you want to predict, is that a little bit there? And those are these distribution functions I talked about. 241 00:23:30,900 --> 00:23:39,270 OK, so what, what what do I do, what other people do? How do we use all of that to do something at the LHC? 242 00:23:39,270 --> 00:23:40,500 How do I put another way? 243 00:23:40,500 --> 00:23:47,820 How do we determine these PDFs or how do we how do we predict what these underlying distributions are going to be that we really need to know? 244 00:23:47,820 --> 00:23:55,970 Clearly, if we're going to predict anything at the LHC? The answer to that is essentially we can't. 245 00:23:55,970 --> 00:24:02,780 And that is because the strong interaction is in the relevant energy regime, strong. 246 00:24:02,780 --> 00:24:07,520 And so these Taylor expansions that Gavin told you about cannot be applied. 247 00:24:07,520 --> 00:24:10,710 And if you can't apply, those becomes very difficult. 248 00:24:10,710 --> 00:24:19,780 And so all of that messy problem of understanding how these corks are moving around, which you then accelerate up and take a snapshot of. 249 00:24:19,780 --> 00:24:25,730 Conflict it. But what you can do is use these things are universal. 250 00:24:25,730 --> 00:24:28,230 The same here, here and here, 251 00:24:28,230 --> 00:24:35,100 and therefore you can measure experimentalists can measure these things in electron proton collisions and also at the LHC. 252 00:24:35,100 --> 00:24:42,990 And you can use that to try and extract them and use them as an input for things like this Higgs production. 253 00:24:42,990 --> 00:24:50,620 And. So where are we today? Yes, what I you open questions, what are we trying to do here? 254 00:24:50,620 --> 00:24:55,300 I've talked you through the basic picture and to some extent that basic picture has been known for quite a while. 255 00:24:55,300 --> 00:25:02,400 But what hasn't been known for quite a while is really precisely what the structure of of of all of those different elements is. 256 00:25:02,400 --> 00:25:07,210 And that's really what we want to know if we're going to do precision physics at the LHC. So there's a whole list of questions. 257 00:25:07,210 --> 00:25:13,240 You know what? I expect you to read them all, but it's just, you know, how much energy is carried by the court, the gluons and the C. 258 00:25:13,240 --> 00:25:16,450 Maybe? What about these heavier corks? I mentioned strange charm and bottom. 259 00:25:16,450 --> 00:25:22,450 They can be in there as well, and you need to understand them for many things. And how well do you understand the connexion? 260 00:25:22,450 --> 00:25:26,060 Theoretically, between everything I talked about in a rather cartoonish way, 261 00:25:26,060 --> 00:25:32,710 a very precise level between the collision and these PDX working all of that out is 262 00:25:32,710 --> 00:25:39,360 what we really need to know to understand Higgs and stress test the standard model. 263 00:25:39,360 --> 00:25:46,660 So we have things called global PDF fits, so fits the parts on distribution functions, fits the proton structure. 264 00:25:46,660 --> 00:25:53,100 And since the discovery of corks, what's really helped here is that there's been a vast array of huge collider 265 00:25:53,100 --> 00:25:56,370 experiments and elsewhere which have allowed us to really map out what is, 266 00:25:56,370 --> 00:26:01,950 after all, a very complicated internal structure with many degrees of freedom. 267 00:26:01,950 --> 00:26:03,870 And that's the way we can do it. 268 00:26:03,870 --> 00:26:10,440 So we combine all of this, you know, the the Tevatron collider at Chicago that used to run that collider protons and antiprotons, 269 00:26:10,440 --> 00:26:15,270 the hara collider at Hamburg, which collided electrons and positrons of protons. 270 00:26:15,270 --> 00:26:21,980 So rather like that deep and elastic scattering process, I talk to you about exactly exactly that process. 271 00:26:21,980 --> 00:26:27,690 And we put them all in a big in a big fit. We try and understand every single one of these processes well enough to fit it. 272 00:26:27,690 --> 00:26:34,830 Of course, you can't read this and I wouldn't want you to. But every single one of these is a given process like of an experiment. 273 00:26:34,830 --> 00:26:38,700 It goes into these things. It gets very complicated. 274 00:26:38,700 --> 00:26:46,080 And here is the data that actually goes into it, and here we are today that really unlike we've ever been before, the data is incredibly precise. 275 00:26:46,080 --> 00:26:51,450 This is really being driven by the LHC, and it's really allowing us to therefore pin down what this proton looks like. 276 00:26:51,450 --> 00:27:00,660 So we have data from Atlas. We have data from at KB, data from CMS, three of the four experiments at the LHC. 277 00:27:00,660 --> 00:27:06,390 We also have data from H1 and these those are experiments that Heracles I talked about. 278 00:27:06,390 --> 00:27:09,870 And there's a lot and I'm not going to go through what each of these is. 279 00:27:09,870 --> 00:27:17,580 It's not important for the current discussion, but what what is nice to see is really the precision the the error bars on these data, 280 00:27:17,580 --> 00:27:24,040 you know, they are, they're just so small you can't see them the kind of cheats a bit because it's a log scale on about 15 or so magnitude. 281 00:27:24,040 --> 00:27:32,060 But take my word for it. Very small. OK, well, it's not just experiment theorists. 282 00:27:32,060 --> 00:27:39,850 And the theory is to match this level of precision, we were going to get nowhere. And it has and we'll hear more about that from Fitbit CEO. 283 00:27:39,850 --> 00:27:45,280 So calculations of these processes that we want to put into the fit, we need to understand well in that Taylor expansion, 284 00:27:45,280 --> 00:27:49,880 we had a gap and talk about where we really it's a very complicated thing. 285 00:27:49,880 --> 00:27:54,910 And so this is this. In fact, this is a distribution to some prediction for that trillion process. 286 00:27:54,910 --> 00:28:00,130 I talked about the electron positron production process essentially versus the 287 00:28:00,130 --> 00:28:05,080 angle that those electrons and positrons get produced out in the collider. 288 00:28:05,080 --> 00:28:13,390 Leading order is the first order now for us. Next to leading order is the second order now for us. 289 00:28:13,390 --> 00:28:16,240 And next, the next leading order is the third. 290 00:28:16,240 --> 00:28:20,830 I think that should probably be for us squared, but no one knows that better than the experts in the audience. 291 00:28:20,830 --> 00:28:25,990 But anyway, you're adding in extra powers in our forecast, you're getting an increasingly precise thing. 292 00:28:25,990 --> 00:28:28,180 Who cares about that? What you care about is this. 293 00:28:28,180 --> 00:28:35,560 Look at the theoretical uncertainty band as you get to that order one percent level, and it's a massive improvement from where we were in the past. 294 00:28:35,560 --> 00:28:40,790 And, you know, I'm not going to even begin to talk about what a five minute contribution to a low end, 295 00:28:40,790 --> 00:28:45,580 non single anomalous dimension in QC is, but it connects. 296 00:28:45,580 --> 00:28:51,230 It's one of those things that connects the PDFs to the processes we measure. And it's rather complicated. 297 00:28:51,230 --> 00:28:59,650 And this is the kind of work you need to do if you can, if you can understand these things. OK, so where are we now? 298 00:28:59,650 --> 00:29:05,900 We've got all that precise data. We've got all that precise theory that's allowing us to pin down this protein structure. 299 00:29:05,900 --> 00:29:11,210 And, you know, two decades after Discovery, which is when this plot roughly speaking was made, 300 00:29:11,210 --> 00:29:15,800 we still only had a very rough picture of how these things looked. And then here we are today again. 301 00:29:15,800 --> 00:29:22,730 I've obviously cheated because a large amount of that is because this is a nice colour plot and that is a grainy black and white plot. 302 00:29:22,730 --> 00:29:25,130 But it's not just that. I mean, don't believe me. 303 00:29:25,130 --> 00:29:31,130 For example, one example because these are rather similar, and don't worry, I will break down everything is in a minute. 304 00:29:31,130 --> 00:29:37,850 I'm on the left hand side. These are just lines that they don't even have uncertainty bans on them. 305 00:29:37,850 --> 00:29:41,300 So they just wasn't enough knowledge, theoretically. 306 00:29:41,300 --> 00:29:47,660 And from data to even say actually, how much wiggle room is there for each of these distributions, how much could they move? 307 00:29:47,660 --> 00:29:51,980 These were just sort of best guesses. Very hard to do precision physics, if that's what we've got. 308 00:29:51,980 --> 00:29:56,090 And today, these are the uncertainty. Bands are not just line thicknesses. 309 00:29:56,090 --> 00:30:00,770 They're really known. It's not precision. So just breaking that down a little bit more, 310 00:30:00,770 --> 00:30:10,040 what does the programme look like here is that distribution and here is the basic picture recovered from this, this plot here. 311 00:30:10,040 --> 00:30:15,150 So this is one of the collaborations that fits these things that could animate that. 312 00:30:15,150 --> 00:30:23,260 I'm the H and. It was actually involved in doing all of that work. 313 00:30:23,260 --> 00:30:24,580 So even today, of course, 314 00:30:24,580 --> 00:30:30,910 with all of the extra precision and the bells and whistles and the extra data when you break it down and you look at the so-called balance structure, 315 00:30:30,910 --> 00:30:38,410 essentially the difference between the up and the ante up. We certainly do see under all of that mess the underlying you picture. 316 00:30:38,410 --> 00:30:45,040 You see a new balance that is twice as big as a down balance roughly two years or up in one day. 317 00:30:45,040 --> 00:30:47,920 And you see that, roughly speaking, to carry about a third of the momentum. 318 00:30:47,920 --> 00:30:56,800 So that basic picture of an up and up and down twice as many ups and downs or carrying about equal amounts of the energy of the proton is there, 319 00:30:56,800 --> 00:31:04,130 but rather clearly there is a broad distribution. So this this is the exhale that's that's been cut off, unfortunately. 320 00:31:04,130 --> 00:31:11,790 I'm. What about forgotten gluons? That's what happens. 321 00:31:11,790 --> 00:31:18,970 So. It's huge. This is the contribution from those gluons that you can scatter off within the proton. 322 00:31:18,970 --> 00:31:22,810 Absolutely huge. Absolutely dominant. In fact, if you work, do the maths stick. 323 00:31:22,810 --> 00:31:30,370 Merck carries about 50 percent of the proton energy to 50 percent of the proton energy that actually is carried by gluons a very important role. 324 00:31:30,370 --> 00:31:36,100 We collide them at the LHC, and that's precisely why we can really study these things. 325 00:31:36,100 --> 00:31:42,970 Study Higgs production, glow and fusion. You've got that that big flux, if you like ugly ones, that we can collide. 326 00:31:42,970 --> 00:31:50,690 So breaking that down a little bit more. We have a plot here from another collaboration site called NPD. 327 00:31:50,690 --> 00:31:52,700 So I'm not going to be biased. 328 00:31:52,700 --> 00:32:00,610 Let's let's go beyond the 50 percent figure, which is, of course, rather rough and not enough for what we want to do at the LHC. 329 00:32:00,610 --> 00:32:04,310 And let's let's let's talk about how well we know it. 330 00:32:04,310 --> 00:32:16,250 So this is just the plot of the uncertainty on the one from dominantly from experimental sources, the data going into the fit. 331 00:32:16,250 --> 00:32:20,330 And there is that baseline. This is a very recent fit, including lots of that actually data. 332 00:32:20,330 --> 00:32:28,130 And what you can see is and this is the reason relevant for the Higgs. So turns out, percent level uncertainty to do very nicely there. 333 00:32:28,130 --> 00:32:34,320 And that's for you. Lots of dedicated work. But why are we doing less nicely? It's a high x said high x. 334 00:32:34,320 --> 00:32:41,120 And what is that? That's high energy. That's high energy Parsons Gap and talked a little bit about physics beyond the standard model. 335 00:32:41,120 --> 00:32:47,030 Well, if you wanted to produce some sort of physics beyond the standard model, it's going to have to be pretty heavy or we'd have seen it already. 336 00:32:47,030 --> 00:32:49,100 And to produce something pretty heavy, you need to collide. 337 00:32:49,100 --> 00:32:53,570 Things are pretty high energy and therefore it's precisely in that region why that would happen. 338 00:32:53,570 --> 00:32:57,860 And yet we have rather large uncertainties. Basically, so far, the data runs out. 339 00:32:57,860 --> 00:33:02,420 So the name of the game there is to really try and pin down as much as we can what 340 00:33:02,420 --> 00:33:09,020 the uncertainty is to really predict how something would look for new physics. 341 00:33:09,020 --> 00:33:12,890 And the other point to make is that we have two curves here, one without LHC data, 342 00:33:12,890 --> 00:33:18,410 and you can see that actually LHC is having something of an effect already. 343 00:33:18,410 --> 00:33:22,820 OK, so the final element is we put the Cork C in these here. 344 00:33:22,820 --> 00:33:28,070 There's no need to break down what each of them is. It's just each is a different flavour of cork up, strange and so on. 345 00:33:28,070 --> 00:33:30,350 But you can see they were broadly the same. 346 00:33:30,350 --> 00:33:37,130 And once again, the only thing I want to point out here is that they clearly some regions carry a lot more momentum and that basic picture. 347 00:33:37,130 --> 00:33:41,390 So again, they're going to play an important role. And sure enough, they do for various LHC physics. 348 00:33:41,390 --> 00:33:43,880 And again, we want to pin those things down. 349 00:33:43,880 --> 00:33:51,560 And if you really stare very closely, you can see that in some cases, indeed, the uncertainty bands tend to be a bit larger than. 350 00:33:51,560 --> 00:33:59,660 OK, so I'm coming to the end. A shopping list of things just to give you a flavour, 351 00:33:59,660 --> 00:34:07,610 not to go into the detail of all the various questions we now need to think about in the future with regards to understanding proton structure. 352 00:34:07,610 --> 00:34:12,710 As I've perhaps given an impression, it's a rather complicated task, including all of that data. 353 00:34:12,710 --> 00:34:15,830 Understanding it all also computationally, 354 00:34:15,830 --> 00:34:23,930 just literally using the predictions that it can be very slow to run and hard to to do to deal with a lot of resources dedicated to that. 355 00:34:23,930 --> 00:34:28,760 And it's not all rosy. What if this high precision data doesn't agree with your prediction? 356 00:34:28,760 --> 00:34:33,980 How do you deal with that? Is that some bias in your your fit? Is it new physics? 357 00:34:33,980 --> 00:34:42,210 What is it? And that's going to that's already some, some some hints of that sort of thing are happening already. 358 00:34:42,210 --> 00:34:48,840 And if we're going to claim such high precision, are there any other theoretical so-called theory uncertainties that we've missed? 359 00:34:48,840 --> 00:34:53,110 I have to go back and re-evaluate the basics and find a nice thing to talk about. 360 00:34:53,110 --> 00:34:56,930 It's just a mention, at least, is that I told you that we couldn't calculate these things. 361 00:34:56,930 --> 00:35:03,560 This part in distribution functions, that's only half true. We can do with consider the strong interaction in the regime. 362 00:35:03,560 --> 00:35:08,510 It's really strong. When we can't use that Taylor expansion in the way we do that is to break down 363 00:35:08,510 --> 00:35:15,260 space time into lots of disparities points try and solve on a giant supercomputer, 364 00:35:15,260 --> 00:35:21,960 so-called lattice. And if you do that, you can get numerical approximations to these things. 365 00:35:21,960 --> 00:35:26,480 It's the very early stage, the various technical reasons why it's rather difficult to do. 366 00:35:26,480 --> 00:35:31,100 But who knows, in 10 years time, 15 years time, we may not even have to fit these things. 367 00:35:31,100 --> 00:35:37,180 We may be able to actually just predict them. And this is all very important for our understanding of the Higgs. 368 00:35:37,180 --> 00:35:43,240 So I'll leave it there and just say I've hopefully convinced you that we we understand the delicacy. 369 00:35:43,240 --> 00:35:46,870 I say not as a proton proton collider, but as a given glue on collider quote. 370 00:35:46,870 --> 00:35:55,300 Collider report comes equipped collider when we understand that and we can really extract the distributions of all those things within the proton. 371 00:35:55,300 --> 00:36:00,850 We don't need to worry about it. We can start thinking about, well, what happens when we collide gluons to make a Higgs and what cannot tell us. 372 00:36:00,850 --> 00:36:13,666 And that's something that, for example, be telling you about in a minute to thank you.