Beyond Higgs: The Wild Frontier of Particle Physics

high, the better, this will work around 13 TV. have 14 and then you collide them, you have a huge amount of energy in that collision and you basically build this gigantic detector, we have four two such detectors, you build these gigantic detectors around that collision point, you know the Atlas detector, which is a The sector I work in is a five story building so it's huge and it basically takes a snapshot of the collision and the collision is messy, it's not like you know a couple of

particle

s here or there, I mean it's how many There are protons in these groups.

Those are hits, I mean the protons that you have, you have many protons in a group, so the beam button is not a continuous beam as you might think it is not like a stream of protons coming in the beam It's designed in such a way that you have like little proton packets that you know well, 10 to 11 around and you have these little proton packets that collide every 25 nanoseconds, which means it's like your camera, your detectors, a camera that takes photographs every 25 nanoseconds, that is, a speed of 40 megahertz and these collisions are so large and occur so frequently that we cannot actually record all the data and we have to make a very difficult decision quickly in a microsecond. about whether this event is interesting or not and this is a big challenge for us experimentally because if you know NEMA comes to me in a year and says oh you know what I think I saw, a new signature would be something totally different and would have been seen like that and if my activation system, that system that makes that decision, was not looking for that, yes or no, the data was lost, I didn't record it, so I can't go back to the data and say, oh, I can look for that , so the theory really guides the experimental approach, it's not like you approach it as a blank slate and say, let's slap these things together and see what happens well, it absolutely is and it's also a very difficult challenge experimentally because on one hand you need be ready for everything your detector can't record everything so you can't take everything so you want to be ready for everything however you need to have made a decision so you need to have some kind of idea about what you are looking for and to have that idea of ​​what that we're looking for so yeah of course we rely heavily on theory and you tell us that because otherwise you know you're at sea we're at sea you're absolutely at sea so Joe of course , you've also spent your career working at a facility that performs these types of experiments, like Fermilab, and over decades, both through Collider experiments and through other types of experiments that we won't get into anywhere. .

In experiments with cosmic rays and other things of that kind we have built what we think may be the fundamental ingredients for creating at least the things that we interact with in the everyday sense and that is the standard model of

particle

physics

, so that I just wanted to review the particles that were predicted and ultimately found, giving us our most complete understanding yet of what things are made of, so we're in the early days of particle hunting, maybe just take us through some of these particles here, so that's it. one familiar electrons all those electrons everyone knows photons the muon was an example of a particle that was not predicted but was discovered and we still don't know why they exist but they are also fundamental particles similar to electrons neutrinos even stranger there I know they exist but They're very different from the particles that you're made of, but that's one of the things we're still trying to figure out and what they don't have electricity, they don't have electricity. charge are very difficult to detect and are very, very different from other quark particles the American murray gell-mann, who recently died, invented the idea of ​​quarks, of which in reality only three of these particles are made, the electron and two of those quarks, the U and D cuts up and down, that's what everyone leaves, that's what you're all made of, but there are more quarks, there's the strange quark that you see there, it was discovered later and the charm quarks, the bottom quarks, top quarks.

They were discovered in my laboratory Fermilab, we are very proud of them and what year was it in 1997 with what was then the largest particle collider in the world, the Tevatron before the LHC, and we don't know why there are so many of these elementary particles , like you, there is a lot more than what you need to create us, so that is one of the things that is still a big mystery and we don't know why they are so different from each other. We have some ideas for that, but it's part of it. The great mystery of this whole picture of the standard model is why it is so complicated in a certain sense and also why it is so simple.

There are simple principles that hold it together. So we see here two collections of particles, so to speak. the ones in the green, which you know on the far right, are different, you know, in a fundamental way, from the ones on the left side, you just draw that thing, yeah, so the particles that you're made of are called fermions. Since when we talk about matter particles, matter particles are fermions and one of the ways to distinguish them is that they carry a small unit of spin that does not actually spin like balls because they are point particles, but they carry a little spin as angular momentum. , so you are made of fermions, on the other hand, the forces that hold you together and keep the universe together are carried by these bosons, these green particles of which the photon is the most obvious example of electromagnetism. but the gluon and the w and the z also carry fundamental forces of nature and those are particles that have a different spin, they have a spin that is actually twice the unit of what the sky fermions are, they are called bosons and they behave very differently, they behave like forces. instead of behaving like matter now nema, so when we started looking at the mathematics behind this, one of the curious features that people recognized even before the theory was fully implemented was that it was a challenge to give mass to these particles and it's One challenge describes why it was difficult to give mass to these particles.

I'll ask you to try to do it oh, okay, yeah, well, it's actually, it's actually a piece of cake, in fact, what we're going to talk about is very much of the conceptual drama of the 20th century in fundamental

physics

and we're going to have I have to count a little bit on my fingers, so maybe before we get to that, I just want to make a general comment about this image is that you could um and it echoes something that's already been said a couple of times, on the one hand , it seems a little complicated, it's not the most complicated thing you can imagine, but there are a lot of particles and it seems a little messy and random maybe, but one of the aspects of our theme we think that the most profound aspect of our theme is that all these things are somehow completely governed and their properties exist, the broad properties are almost entirely dictated by great general principles, these two revolutions.

Previous principles that we learned at the beginning of the 20th century from the laws of relativity and quantum mechanics. It turns out that these laws are almost incompatible with each other. It is not even remotely obvious that they can be equalized. You knew about toy universes that were compatible with the principles of relativity and quantum mechanics, but you can barely do it, and if you help sufficiently competent theoretical physicists, you lock these laws in a room and refuse to let them look outside and just say what you could do. If you can think of something that is possibly consistent with these principles, then this is the kind of thing that, in a sense, arises from pure thought once you include, of course, these two big facts that we have observed experimentally: that the relativity and quantum mechanics are both.

It's true and a very important aspect of this and a very important reason why it is so restricted is exactly this issue of the difference between being massive and having no mass, so let me try to describe this. We just talked about the photon and as Joe mentioned one of the properties that the photon has is that it has a little spin, if you're familiar with just thinking of light as a wave, classically it's an electromagnetic wave, sometimes we talk about that. it has polarization, okay, it can spin one way, it could spin around the Otherwise, well, what really happens is that the underlying photons that make up a light have a little spin so that they can spin in the direction that they are going.

They move or in the opposite direction to the direction in which they move, and this is a crucial fact that they can Now spin in two directions, the other particles, such as the W and Z particles, are massive cousins ​​of the photon, but the mass does not It's a small correction. If you are very naive, you would think especially when we go to these huge accelerators. We crash particles into each other at incredibly high energies, surely when the energies are enormous you can ignore their mass so that e is much larger than M, so you could basically ignore the mass and you can get incredibly At high energies, you can think of the masses with a small perturbation and only talk about massless particles, but it is not true, it is not true because massive particles that have spin one, I have rotated twice to spend the electron, we say that it is spin one.

The W Mzee have three ways they can spin, while the photon has to and what is the difference between this 3 and this 2, no matter how fast this W particle moves, let's say, you can always catch up with it, you can always catch up. move and reach for it, let's say it was turning this way, by tilting your head, you could see it turn from side to side, as well as reach for it because it's huge, exactly, that's true, that's the crucial point, because it's huge, it doesn't matter . how fast it moves, it doesn't move at the speed of light so you can catch up with it, while the massless particle like photon moves at the speed of light so you can't catch up with it and therefore , you can't play this. game in which you tilt your head and watch it spin in all possible directions in the three possible directions; in fact, all you can do is conclude that it is spinning in the direction it is moving or in the opposite direction to the direction it is moving in this Not equal to three business is really deep, it means you can't think in mass as just a small correction to things that no longer have mass and, in fact, precisely for this point, if you try to describe the possible types of composition and interactions. of massless particles then it is essentially a mathematical theorem that follows again from the general physical facts about the presence of relativity and quantum mechanics, but the types and interactions of massless particles that you are allowed to have have to come in a lowercase variety, okay, so the menu of particles you can have that can interact in a way compatible with the principles of relativity and quantum mechanics is as follows: Particles can have spin zero half, that's the unit you have the electron. just a convention, so one three halves and two, that's it, that's all you can have, plus there can only be one of those spin-2 massless particles, so we're not going to talk much about that today, but you can only have one of them. and if you study its properties which are imposed on you by relativity in quantum mechanics you will discover that it makes massive particles go around in orbits etc, gravity is fine and then all the properties are dictated by these basic principles of The Special Theory from Einstein's relativity and quantum mechanics, then spin-zero particles, well, you can have as many as you want, spend half as much, you can have as many as you want, spin-1 massless particles have two very special properties and they interact . each other in very special ways, you can have a massive expenditure of three particles, they have to be even more special, we could get to that later and like I said, massless spin-2 is associated with gravity, so that's Everything, there's kind of a tiny menu of possibilities that you're allowed to have and nature is making use of that menu as far as we know, so we've seen the set of possibilities before July 4, 2012, we had seen nature make use of some of these possibilities.

I had used spin 1/2 particles spin 1 particles and of course this has been associated with gravity. One of the most interesting and important things about the Higgs is that it is the first example of an elementary particle that has no spin. that we've ever seen, so it was added to the mix, but the reason the Higgs had to be there is that something has to account for this, it doesn't equal 3 businesses, ok, something has to explain it. where the mass comes from, not only not only to add this number to the actual mass of the particle, but also to take into account these additional things, these additional ways of spinning that things can spin when you give them a mass. rotating particles. and that's the whole story of the Higgs, it'scertainly not what attracted me personally, yes, to fundamental physics.

I don't care much about the basic components of matter, it's a lot like chemistry. I was bad at chemistry in school and I don't care much. about the basic components of matter, I care about the structure of the fundamental laws of nature, yes, and we have learned that elementary particles are the letters of the novel that interest us, the novel that we are We are interested in the structure of the laws of nature and that is what we really care about, a new new principle, a new phenomenon and from that point of view the Higgs is very new, it is very strange that we have never seen anything like it before. so I think the main thing for me and I think most of the people proposing these future machines the main thing that we will learn for sure by doing these new experiments are fundamental facts about the Higgs: we have never seen an elementary particle like the Higgs before.

We have to put it under a very powerful microscope, more powerful than the one we have at the LHC, and the main drama about the Higgs is whether it really seems elementary or not, whether it really seems punctual or not, from the LHC we are going to get a pretty blurry image of what a point like the Higgs looks like, you really have to set it low, and in fact it's blurry enough that we've seen more or less analogous things elsewhere in particle physics that most of you probably haven't heard of. In this particle there is a very important particle known as PI which, at first glance, also looks like it could be some kind of elementary particle of zero spin, but very quickly you see that when you put it under a magnifying glass with five times the magnifying glass, Let's see that in It's actually made up of little quarks held together with glue, so all the theoretical drama that might have been there with the Higgs wasn't really there with the PI in place.

That's the resolution we're going to get in the LHC's Higgs, plus or less the same kind of factor of five resolution that we had with the PI on. We need another factor of 10 on top of that to know if it's really something new. if it is point like we actually expect in the standard model or if it has some subsubsubstructure, then there are two types of experiments that we can do, one is to see if it looks a lot like two other things like I literally want to see what a point looks like like if You'd like to see what happens when a photon bounces off the Higgs, of course the Higgs doesn't actually live long, so it's analogous, if the owner is proven to hate it, it decays the two photons or other things. and then you see if that interaction of the Higgs with other things is compatible.

The highest point is what these so-called Higgs factories will do. The linear machine that Monica was talking about is a great machine to do this, it would produce millions. of Higgs particles in a very clean environment, in fact, these 100 kilometer circular machines could do exactly the same thing if the same electrons and positrons collided in them, so one of the best things about these circular machines is that they could fulfill a dual function. You could first collide electrons and positrons, produce millions of Higgs particles and see if they seem to target external probes like photons and other things that they might run into and then ultimately, if you go to the hundred TV colliders, if you collide protons and exactly.

With the same machine you can ask and solve the question of whether the Higgs looks like a point ultimately to itself and that's a fascinating thing. The simplest interaction that elementary particles can enjoy is when three of them meet at a common point in space and time and it turns out that there are no other elementary parts Engle's elementary particle actually has this interaction everything else we know there is something that changes some changes in some properties the Higgs is the only elementary particle that can have as a dominant interaction this interaction with itself and therefore By looking for this interaction it is not only the first time that we see the simplest type of interaction possible in the nature, but we also check whether the Higgs really seems to point even at itself, the LHC is not even going to tell us with confidence if this interaction even exists, but the Hundred T V Collider will produce billions of Higgs particles and at the same time Doing so will not only tell us if they exist, but I will measure it with a small percentage of precision, so I just told you what I think and believe. most of the people pushing for this next generation of accelerators are not promising, oh we barely knew about supersymmetry, it could be around the corner, that could be true, okay, but that's not the logic of the argument, At this point, the logic of the argument. to do with the fundamental type of paradigm shift that challenges the nature of the Higgs itself and the fact that theorists are confused. 40 years of ideas about what might be associated with the LHC but what the Higgs certainly has not been have not been widely confirmed in the The LHC is not even close when theorists are confused, more experiments are needed and experiments need to be done about what confuses the Higgs, is what confuses, so we have to put it under a very powerful magnifying glass, very well said now, when we look. in the big principles, so one thing we can do is smash harder to magnify more and try to see the fundamental structure that we may have overlooked, etc., but in terms of general theoretical paradigms that will guide us forward, so So don't rule out supersymmetry, it might still be part of the story, but what I mean might just go a little further, Joe, what would you say?

I mean, obviously, there are things that people have in string theory, people that have supersymmetry, there are other things like Technicolor that people have talked about. You feel like we have the guiding theoretical structure that really gives us a clear path forward as to what we should be looking for. I think we're in one of those periods in the history of physics where we really need the guidance of the data, that's us. I have ideas, some of them I'm sure are good, but we need, we need more, we need nature to tell us more about what's really happening and this has been a more typical situation in the history of physics, so you know , have confidence. and you know, Dirac was, like I said, the lucky guy who had the idea and then the experiment came up, that this is the typical situation where we have some ideas, part of it is probably right, part of it is probably wrong, probably there is something missing and we need data to figure it out and that's what these more powerful instruments are really for there is a nightmare scenario that you described for the LHC did you imagine that some next machine would be built what would be your nightmare scenario there well, actually I think I know that I've looked back now, nine years later, and you know, a lot of data later, we didn't have any data at the time, so we were kind of, you know, I definitely had, let's say, an eye-opening experience as well. of the whole thing and I think basically supersymmetry basically did us a disservice experimentally, let's say because it sort of set this expectation, I think you know that the LHC was going to be the discovery machine in the sense of discovering particles and the LHC has It has been a discovery machine and I think you know it because we have learned a lot, the LHC has given us many precision measurements of the standard model, the detectors we have are beautiful, they are impressive, the amount of precision we can get from these detectors is amazing, It's really been an absolute success in terms of what we've been able to measure and, as I said, we discovered the Higgs in 2012, no one expected our detectors to have that precision at that time.

We have been making measurements that we never thought of. I mean, Nima says we won't be able to measure Higgs self-coupling, but you know, we're doing studies that show maybe we could start accessing it, and so on. so I think we've made tremendous progress in technology, we've made tremendous progress in precision measurements of the Standard Model and I think this idea that you know particle physics is about new particles really didn't do us any favors. and in this comment that I let you know ten years ago saying that it would be Higgs and Hicks only that it is the worst case scenario is absolutely a reflection of that time.

I think it's a reflection of how we were seeing progress at the time and I think we all have. There has been a big emotional shift in physics in the sense that exactly as Joe says we need the data, we need to know the Standard Model better before we that we can really say, we are going in direction B or C and that Really, despite its successes, despite how much we know about the standard model, we have all discovered that it is not enough, yes, and these next generation machines are exactly that, so in that sense, my worst case scenario would be pretty much a you know. a fire in the cave, I think you know, yes, a real disaster.

I think we're at a point where the most important thing is that we've seen this phenomenon that we've never seen before, so I think it's very funny that in a sense, seeing the Higgs and nothing else until now is, by far, the most shocking thing that could have happened as a result of the LHC experiment. It is the biggest challenge for theorists. Shakes the conceptual foundations. beneath us more than we had seen these things we expected for decades. It's actually funny when I was a grad student there was such an expectation that something like supersymmetry was correct and that was an idea that people came up with in the '70s and '80s and the job of my generation was to clean up. the details and figuring out how precisely it broke and worked, etc., and that's definitely not how it worked, in fact the challenge became greater, it became much greater and the stakes became more structural. than about this or that detail or this or that additional particle like that.

I can't emphasize that enough. I think the last time an entire community of theoretical physicists was so stumped by something and came up with experimental results that didn't line up with what they expected was when we expected the universe to be full of ether and the absence of ether, a null experiment was the harbinger of coming revolutions. This idea that a whole generation of particle physicists grew up with that the glory was the The 1960s with a particle every week, it's true, it was a wonderful period, but that was not the case, in 200 years, this will not It will be the best of the 20th century, the great thing about the 20th century was relativity and quantum mechanics, and there are many and There are many very important details after that, but these types of discoveries that are so revolutionary and conceptually transcendental do not have that character, yes, They had their surprises, they involve things that happened, that you wouldn't expect, so I think we're crazy, we're in another one of those periods today and the heat isn't the only thing you know, have you spoken eloquently on these shows or have there been many, many years, there is another very important experimental impact on the system. in the late 1990s when we discovered that the universe is accelerating well and these are two different classifications, the expansion of the universe is actually accelerating and the qualifications are two very theoretically from a theoretical point of view, but they are shocks very closely related that our fellow astronomers want We are going to measure the expansion of the universe and our part of its experiments, we are going to measure the Higgs and these are actually very closely related conceptual mysteries.

I think I'm certainly not the only one, but I definitely think we're in another one of these periods that happens every 100 years or so, where the issues at stake increase an order of magnitude in sort of structural importance and in many ways the Higgs is the most important experimental actor. in history because it can be put under scrutiny, okay, it can be put under a powerful microscope, it can be put under scrutiny, yeah, so all this talk about deceptions and nightmares, etc., I think it's a little crazy, you know ? just because you're In these conversations I need to play devil's advocate, but in 2010 or 2011 I wrote an op-ed for The Times in which I wrote about finding nothing unexpected at the LHC as one of the most potent possibilities that could emerge as In as opposed to this standard mood that you're expressing, which is that particles find more products and more particles, so I totally agree, but I want to end with a point related to the note you just made about accelerating the expansion of particles. cosmological ideas.

I just want to end on a cosmological point, Joe, you've written about a curious feature of the Higgs phenomenon, which is that you know that in the early universe, at least in many conventional formulations, the Higgs field wasn't actually permeating space. , so I was just a little bit. A little bit later, the universe went through a kind of transition, yeah, where the Higgs then permeated everything, so it went through aphase transition, a very radical change of sorts, the particular application of the Higgs field that we found suggests at least the possibility that we might be facing another such cosmological change in our future, so given that it is a very bright note for conclude, maybe you can describe what we are referring to at the end of the universe, yes, exactly as you said, we believe that the cosmic universe molasses was not always there, it actually turned on the Higgs, it activated itself, if you will, at some point moment of the early universe is all about phase transition, so you can ask the question: will the cosmic molasses just stay as it is? is it forever or at some point something else will happen that involves this and there is a calculation that you can do at least with those standard model equations that we have now that we know the Higgs boson and its mass, we have all the numbers. that it is necessary to do a calculation like that and some of our colleagues have done these calculations very carefully and interestingly it seems that we are right on the edge of the universe that will eventually want to change into something else, it seems that our universe is slightly unstable: in At some point a little bubble of something else will appear where the Higgs is doing something else or with a different value and once that bubble appears it will expand at basically the speed of light and eventually reach us. and I'm going to get to us and that will be our end, although it will be a different universe, but we won't be there now.

Singing, even if this calculation is correct, you would expect this to happen incredibly. in the distant future so it's not I don't think it's more like it's on the order of ten to a hundred years from now so even in the billions of billions of years it's a very long time so you shouldn't worry For this. I got an email from people saying I can't sleep at night because I'm worried about this. I always answer you. You know you have a lot of other things you should worry about, but this is not one of them, but two two-particle physicists.

It's an incredibly profound thing, it's a question of what the forever Higgs really is and if it's not forever, what that means and one possibility is, again, that this leads back to ideas like supersymmetry, if you think so, that nature should stabilize universes, then you need some ingredient that we should add and what is that ingredient, right? We know what we assume you might also respond to people with that concern, since this bubble of some sort of new phase is expanding at the speed of The light when you see it will be upon you, yeah, you don't have to worry, don't worry.

You'll see it coming, you'll just look like you're inside this bubble, you know, because what's happening is the heat is getting a lot bigger. inside the bubble, that means every particle in your body that has mass becomes much more massive on the inside, so anything massive crashes well, you know, they're stars, you and me, everything would crash into this, except light, light passes through, so if you or one of your descendants manages to get inside the bubble and run at the speed of light to maintain the width of the entire bubble, it's literally like being inside. of a car with flies on the windshield.

I know that the entire rest of the universe is just going to burst into this bubble as it passes through you, so that's a very encouraging thought. There's a couple of minutes left and I just want to give everyone a chance to say sort of the last word. Compared to where we were, say, 10 or 15 years ago, do you think we've gotten to a more exciting place? Do you think we have gone through a stalemate? I mean, how would you characterize the state of particle physics? being today maybe is the right thing I always remember when I was going through a really frustrating time as a grad student, a senior grad student and my group were saying if it were easy it would have been done already and I think that really describes where the particle physics.

Right now there is absolutely nothing about particle physics that is easy and I don't think I know any particle physicists who got into this field because they wanted it to be easier, so in that sense I'm personally excited about the challenge. what will be Hard as hell to build experiments for these new carbon lighters, bring it on, I'm ready and I'm ready to take the Higgs measurement, just as we can, well, NEMA, well, tell him my graduate student said I could come. go back in time and control when he would be born. I wish I could enter graduate school today.

I really think, I really think that, from my point of view, it's the most exciting time in fundamental physics, without a doubt, in 50 or 60 years, maybe. Going back to when relativity and quantum mechanics ended up being a thing and, um, and it may seem crazy, I mean, you know, there are other people wandering around, they're a little depressed, we've seen the Higgs. and nothing more, so who's right, you know, they may be on drugs or they may not be drugs, what and I think it really depends on why you got into this business, if what really motivates you is trying to understand something profoundly conceptually new about In the world, that kind of opportunity doesn't come around every ten or twenty years or so, most people don't get to experience that and I think we're at the point now, after looking at all kinds of easier questions, where you know that in science Are you motivated by gigantic questions but have to work on the next question?

You have no choice but to work on the next question. Well, we are finally at the point where the next questions are gigantic, they are existential in nature. what are space and time, what is the origin and destiny of our enormous universe, why can large macroscopic structures exist when there are enormous fluctuations of quantum mechanics that seem to want to destroy them, etc., these questions even seem to be interrelated between yes in some ways potentially and our generation of people is the generation in which we will work on these questions responsibly, it is meaningful for us to work on them because there are not ten other questions between us and so, that's why I would like Let's say it's like if you wanted to climb Mount Everest, first you have to, you know, get on a plane, go to Kathmandu, find the Sherpa foothills, all kinds of things, finally we get the right base camp and you can see the beast for the first time and then decide what.

Do you want to do you want to wait for oxygens to be invented, oxygen masks, otherwise you might go up and die or you start trying to climb somehow that's where we are I think we're at a point where we're finally looking at these deeper questions. about the nature of reality and we get to work on them and we get to work on them as theorists and we get to take on the powerful challenge on a generational scale of attacking some of these questions as experimentalists, so I think it's a fantastic time. to be a physicist, but you have to understand that you have to be in this business for the long term and it is possible that you will spend 3040 years and that you can easily die without having made substantial progress on the issues you are asking yourself. interested in but that's what you have to do if you're interested in this kind of stuff Joe, yeah, along the same lines, talking to someone who's in a big national lab, if you look at what our young people are doing now in these labs They're motivated by big scientific challenges, they're trying to develop new technologies to build us these better microscopes that we know we're going to need to make these discoveries, and so those technological challenges are equally fascinating and interesting as these scientific questions. that are motivating them and I think that kind of cycle of these big scientific questions that motivate us to push the technology so that we can do the experiments that we haven't been able to do yet.

I think it's a very virtuous circle and it's one of the things we do for society that is really important, grateful, it's been a fascinating conversation, join me in thanking everyone.