WSU: Accelerate, Collide, Detect with Barry Barish

i'm going to tell you today about particle accelerators and which have been the primary tool to do particle physics for 50 years or 60 years in the spirit of full disclosure i'm not an accelerator physicist i'm a person who works with ray weiss who people here next on ligo and i've spent most of my career doing particle physics physics as an experimentalist but i know a lot about accelerators i helped design this one or i led the design of this one and when i started in physics as an undergraduate the first thing i ever did was work in berkeley on the 184 inch cyclotron as a student and have always hung around accelerators my whole life so i'm going to tell you about why accelerators are important to particle physics i'm going to use as the case example the one that we've designed which is the the dream of particle physicists to be the next accelerator and it's proposed to the japanese government right now who are doing due diligence on it and a little bit about the future because there's a question about whatever happens what's going to happen in 20 or 50 years to particle accelerators which get bigger and more expensive in each generation so i'll try to talk a little bit about each of those but mostly about accelerators so about a linear collider so let me introduce the subject a little bit starting from particle physics to drive the discussion and this picture is one of many you could use to say what is particle physics there's a whole kind of potpourri of questions and areas that we study varying from [Music] looking at very very rare things decays of k-mesons or other particles studying neutrinos which have been very popular and productive in recent years to working directly on particle accelerators and studying the higgs which came out of the large hadron collider or a bunch of other things some of them done underground and so forth and they come back to something that isn't just a single purpose a bunch of let's say theoretical ideas that might be where the overall picture of particle physics which we don't have yet can come together whether it's the unification of the forces or whether it's some connection to cosmic things or uh ideas that there are more than three dimensions in the dis discussion of particle physics so there's just examples and people can make different kinds of pictures a list of questions i'll give you here which is not mine but comes from a little handout on particle physics called the quantum universe which gives you just some picture of the breadth of questions that are asked all of which cannot be answered by particle accelerators some of them by satellite experiments some of them deep underground but the majority of them the biggest tool and most effective tool we've had for 50 or 60 years is particle accelerators so an example of the kind of questions are whether there are some fundamental principles that we don't understand yet new symmetries in nature the picture that i'll come back to later is something called supersymmetry whether there's a particle physics answer to the question of dark energy or dark matter whether they're extra dimension something i talked about before what are neutrinos all about and what are they telling us we have the fact that neutrinos have different masses why do we have the different families and so forth and so on so that's more or less this big scope of questions that we ask and we have different tools to answer them and i'm just going to talk just about one of them today so the main ones that have been so productive in recent times are neutrinos which basically are useful both in understanding the neutrino which we have to understand and in the fact that the neutrino doesn't interact very much so when it interacts we can understand the interactions very well and so it's been a very very useful probe of both physics beyond the neutrino and the neutrino itself where understanding more recently that neutrinos have mass has been an important advance in particle physics the second which has been important in recent years is what connections there are between particle physics and astronomy and astrophysics the most logical one is dark matter it may have a particle physics connection which means you have kind of a double win when you find out what it is and the leading candidate being for example supersymmetry or maybe the dark matter is not connected to particle physics but at least the particle physics connection is here and it's looked for on the on large accelerators and it's looked for underground and in other ways and then we have accelerators which is what i'm going to concentrate on and we know and have heard a lot about the large hadron collider which basically scatters protons off protons and the thing that people know best is the discovery of the higgs boson which i'll address in terms of what a new accelerator might tell us about the higgs boson and lastly and that's where i'm going to concentrate is electron positron colliders and in particular in my case i'm going to talk about a linear collider which is a new kind of tool and technology that we're driven to if we go to high very high energies so let's start with accelerators and what the general principle of a particle accelerator is they work in different ways but this is a generic example that you have an electromagnetic wave that you create that's passing in down in space or classical machines just did it in one time one place around a machine but typically you have a machine that has an electromagnetic wave and the little picture are the particles that basically might be trailing or might be leading the the uh the group of particles and you want them to be in a bunch because that's the way we can best experimentally study them is put them in bunches where things happen and we look at that bunch of particles and that happens naturally in this picture because the ones that are here have the highest field and they catch up and the ones that are here go slowest because they're not pushed as hard and so you get a picture a little bit like this thing on the right where they tend to bunch up so you can naturally bunch the particles which you want to do if you create a traveling wave that looks like this so that's just a principle the second thing which i want to emphasize is that we learned in the 1970s or maybe we learned this principle earlier but we were able to make the change particle accelerators until the 1970s worked like the top picture you made a some sort of an accelerator a cyclotron or a synchrotron or a higher energy machine or a linac and took those particles and ran them against the target if you want to make the target simple so you could understand the physics this was typically a proton target meaning hydrogen and studied the scattered particles if i take as an example a beam that's high energy like we talked about today say 450 gev and scatter it off a target at rest the total energy that we get in the center of mass which is the physics that we talked we're talking about how much energy we go to or how short a distance is calculated by this formula here and that gives 29 gev if instead i can have the 450 gv beam scatter off another 450 gv beam what we call a colliding machine then you get far more energy 900 gev and here's the formula so that's just kinematics but it's crucial and that's where we made the switch so the big switch in particle physics was not just the advance of better and better accelerators but the change to accelerators that we call colliders and that happened in the 1970s the first big one was built at slack and i'm going to show it in 1975 and it was responsible for studying the whole new series of particles charm particles b mesons and so forth so that's basically why we use colliding beams and i'm going to talk about colliding beam machines this is a picture to show you what happens in an old laboratory this is now the biggest and most successful laboratory in the world there's a cern laboratory in geneva switzerland and this is all the rings they have they often talk to each other and there's states next to them so you can see going back some of the rings go back to 1950s this is the proton original proton synchrotron and they're all over the place in the laboratory when you go there is kind of not by design but by evolution has built large rings where this biggest one up here is the large hadron collider where there's two detectors one of them shown here one of them shown there for doing high energy physics and these are the two that studied the higgs boson and the third detector and fourth detector that actually are used in a specialized way to study b mesons or heavy ions okay so this is kind of the features that we have to deal with if we have a collider like the large hadron collider at cern in order to study the physics we want to we need high energy it goes up to 7 tev that's 7 10 to the 12th ev it has a large number of particles in each bunch where i showed you that we bunch them together 10 to the 11th particles an enormous number and we want to reach a luminosity luminosities as units here so that if you multiply the luminosity times time you can calculate the number of collisions so that we can see that the physics that we want it needs a luminosity in this these units of 10 to the 34. the event rate using that in one of these two detectors that i talked about is huge it's 10 billion interactions every second so these experiments have to sort that out somehow it's a huge number most not very interesting a proton scatters off a proton mostly what it does is just graze it does something so we know it's not just going through but it's not really the physics that we talk about that's called soft basically it doesn't scatter very hard it's scattered electromagnetically or some other way and there's a huge number of those and they go into any detector that you have something like 10 to the ninth of those per second the interesting ones are the ones that make really hard collisions where there's a lot of energy transmitted from one of the particles to the other and for example the higgs boson happens very rarely and it accounts for about 1 in 10 trillion of those collisions so that has to be sorted out in the detectors and so one of the reasons we talk more about the detectors and the detectors are so challenging and the science is so challenging you don't really hear as much about the accelerator that enabled it is this is a huge job to be able to pick this out this is just a picture of the cern machine with some of the parameters it's 17 miles circumference it's deep underground which protects you from the radiation it's 300 feet underground it has it's super conducting meaning that it runs uh at low temperature where you can get higher fields and uh it uh has a huge amount of stored energy in it something like 10 000 mega joules of stored energy and there's this huge number of collisions which i talked about and it runs at 14 trillion electron volts just as a comparison just to think about it uh a proton beam that stores 700 megajoules is about equivalent to the energy in a 747 taking off or enough energy to melt about a half a ton of copper so there's a huge amount of stored energy which we have to worry about if we ever have to dump it in the machine because it's circulating the machine most of it not interacting and not giving us particle physics okay so we as i mentioned we developed these particle accelerators that can be colliders in the 1970s and the one that i'm going to concentrate on is the electron positron one not the proton one i'll explain to you why and we've had three generations of those and i want to point out why i just historically first were interested in a fourth generation the first generation was the spear collider at stanford at slack and that was quite successful as i'll show you and the second generation was in germany at the desi laboratory called petra the third generation was at cern called lab and we're talking about the fourth generation now and whether it'll happen so that's the one i'm going to concentrate on but let me tell you a little bit about the first three and to do that let's talk a little bit about the difference between proton proton and electron positron collisions and why electron positron collisions are so valuable even though they're so much harder to do it's harder to make a machine to and i'll explain why this accelerates electrons to high energy and makes enough collisions compared to a proton machine protons are complicated they're made out of quarks like the little indications here or what we call gluons what holds it all together under quantum chromodynamics so we basically have a complicated object hitting a complicated object and the actual hard scattering that we're going to look at involves one of the objects one of the constituents in one of the protons hitting a constituent in the other proton but you don't know which one it is so it could be a one of the quarks you don't know which one it can be a gluon you don't know which whether and you don't know exactly how much momentum this one happens to be carrying of the proton the proton's momentum is carried somehow in this combination and so when you have the scattering you don't know very much about the initial state then you have a a lot of things that happen and you and look at the final state if instead we go to the second one which is electrons and positrons the initial conditions are totally well defined we know an electron is a very simple particle we have one of different charge but we know its features we know when it comes together it annihilates all the energy which isn't true here all the energy goes into the final products and it doesn't have all this so-called soft scattering so essentially everything is useful in making high-energy collisions because it just annihilated and uh it that therefore produces what i call particles democratically which means it doesn't favor some particular physics over some other physics which enables you as i'll show you to produce things like higgs bosons with a much larger fraction of the data and lastly if you are good enough on the single event you can reconstruct everything here you couldn't possibly do that here because you don't know what the incoming conditions were but here where i know exactly the direction the spins and the energy of the incoming system if i was good enough and could make a detector that was good enough i could study in absolute detail what comes out in practice we can't quite do that some of the particles that come out for example neutrinos we can't measure we can't always see neutrons and photons the invisible particles and sometimes we can't separate them if they're too close together so we can't make a perfect detector yet or at this time but we can do a lot better than here so we're somewhere in between looking for a needle in a haystack here where we have mostly background and being able to see the events here so let's look at the history a little bit the the development of electron positron colliders like most things the first idea actually was in the soviet union and was published but not a a as a concept but the first development was actually in italy and it was this man here bruno tushak who built the first successful electron positron collider this is the first one called ada and then he built several other generations he eventually managed to get up to a center of mass energy of 3gv and you've never heard of this guy he's the hero in the field and it's almost an accident because at 3.1 gv the world changed and that was the discovery of charm particles the psi particle and so forth and that was done a generation later at slack but only a few percent more energy which produced this particle where the topology looked like this and it was given the name psi it also provided the discovery of all the charm particles and changed particle physics the second generation which was a desi was important for another discovery it managed to discover what we call our gluons in the lab but it was really the laboratory proof of important concept and strong interactions in particle physics which is quantum chromodynamics so the proof of quantum chromodynamics came from this experiment seeing features of gluons at the desi machine and these three gentlemen won the nobel prize the theorists won the nobel prize for the quantum chromodynamics which this confirmed and the last generation that we've had which is at cern is the lep collider and it it has been responsible for to one thing mainly which is confirmation in great detail of this what's called the standard model of particle physics that's called a model not a theory so the the whole problem that we have is how do we get past the word model but it has many many measurements all of which agree within statistical limits within a couple sigma of the predictions for different channels and so forth of the standard model it uh also searched for the higgs boson but a little bit like mr tushak it went up to here the yellow part this this part and went up to about 110 gv before it was limited by radio frequency power in the machine and the higgs boson sits at 125. so this could have been discovered a decade before in a clean way on this machine if it had gone 10 percent higher in in energy but the potential as you can imagine is here because i'll show you what the e plus e minus machine can do so that's the background uh we can have particle colliders then that look like this a set of magnets to make particles go around in the circle uh they come together at some point and if they collide we detect them in our detectors and in the meantime if they don't collide that goes around again and they try to collide on the second time what i'm going to talk about today is what's called a linear collider this is a schematic picture of the linear collider that i'll describe and it has a different set of problems but first i have to tell you why it's a linear collider so we have circular colliders and we want to go to be to understand why we need a linear collider it's a new technology it's very challenging i'm going to go through it in some detail but first let me try to show you why we need it the problem is that on a circular machine electrons are very light and if we send electrons and we we accelerate them around a radius to keep them in this in in a ring so we can have counter rotating rings they radiate they radiate by what we call synchrotron radiation and that depends on the mass of the particle and the energy of the particle protons which are 2 000 times heavier than an electron basically also synchrotron radiate but not very much so this is a problem for electrons that's why we don't talk about linear colliders for protons we only have to talk about it for electrons this is the formula for the energy loss in this radiation so the loss of energy goes as the fourth power of the energy so we want to increase the energy of an accelerator we rapidly run into this problem and inversely is the fourth power of the mass which is why the proton is not such a problem but the electron which is 2 000 times lighter is and the cost then is some combination of the radius or the circumference and the amount of energy you lose that you have to pump back in if i minimize that i can then optimize and the radius for a machine in an electron machine you can calculate goes as the energy squared and therefore the cost goes as the energy squared so we have a picture that looks like this a circular collider as we go up in energy the costs will go up in energy optimizing it for how big you have to make it and we know the cost of these machines get very expensive when we change without not solving the problem of how to make a linear collider yet eventually a linear collider will grow linearly with cost approximately and so eventually these have to cross each other if i take these costs together and try to do a realistic estimate that crossover is at about 200 gv which is that energy that you saw left go to so left was more or less the highest energy that you can go to in a circular machine in a reasonable way you can make a bigger one but basically that's the optimization so going to a tv which is where we want to go uh requires a different technology and that's what drives us to a to a linear machine so this is the picture of the linear machine which i'm going to deconstruct for you and show you the different and important parts of that machine it's drawn out of scale but there's different elements that are here these are the long linux so this acts like two rifles pointing at each other and but we need to do a lot to make those rifles have the kind of beam that will actually hit each other and we'll have the characteristics that we want and i'll describe that to you that's the scale is that the total length of the machine that's being compared and being proposed and being evaluated in japan right now is 30 kilometers long in its initial version and it's upgradable to twice that which is about 50 kilometers long so it's the program is to make a 30 kilometer long machine that could be extrapolated to be extended to one tv are and this is one tv which is to be compared with 14 tev in the proton machine the lhc but as you saw in the pictures earlier that a 14 gv lhc mostly has only one constituent carrying part of that energy in one in one direction scattering against one of the constituents in the other direction and the typical center of mass energy for the constituents is more like this energy so they're comparable to each other this is a picture a schematic picture of the machine at cern it's 27 kilometers long it's about 100 meters underground and has four experimental stations and it goes in a big circle likewise the linear collider is planned to be about 100 meters underground and it's just a different geometry it's about 30 about as much length but it's 30 kilometers long linearly and it follows the curvature of the earth in contrast to ligo which you'll hear about next which has to be laser straight this follows the curvature of the earth i'll tell you now so i won't forget later for two reasons one is that uh if you go deep underground you want to make a geology that's stable to put this big tunnel in and the layers of the earth tend to be in in strips and so to stay for 30 or 50 kilometers in good geology you want to follow the curvature of the earth that's a practical reason the second one is practical also the the machine itself is cryogenic it has a big cryogenic plant to cool down the uh system these are i as i'll show you our rf cavities that are cryogenic are run at low temperature and so you have cryogenics that are on the earth's surface and cool the the the device and if you have a a laser straight device then it's not going to be perpendicular to the earth everywhere and so the cryogenics and fluid are going to want to flow one direction or another if we follow the curvature of the earth then in any place locally the cryogenic stays so we follow the curvature of the earth and in contrast to ligo which is a light beam we can make little corrections and and do that without affecting the optics very much so that's just a decision that's made this is just a picture schematically i'm not going to describe it just to show you the scale the large hadron collider is made out of 15 meter long cooled magnets and they look like this and they're 15 meters long so the naked eye the linear collider looks almost the same it's 15 meter long roughly units about the same diameter the guts are completely different in this case we have cavities and not magnets and and cooling and so forth it's done in a totally different way but for a practical matter of putting together an accelerator it looks pretty much the same we have units that are about 15 meters long that are tied together cryogenically and electronically so let me compare the features again uh i've said many of these so we're going to have uh in the ilc electron positron collisions versus proton proton collisions the center of mass energy is a half to one tv versus 14 tv but we don't get to use for most collisions much of this 14 tev the luminosity is more in the ilc than in the lhc because we're trying to do very precise physics and need the statistics the accelerator type is linear compared to circular so this kind of summarizes what i've said and it's superconducting rf versus superconducting magnets so they're both cryogenic but different okay now let me start showing you why it complements what's done at the lhc and why we want it first i'm showing a non-complementary picture of the higgs discovery and it's not the most recent one so but basically this is on a linear scale usually when you see it there's a suppressed zero and the data is shown here and the line through it is a simulation of what the all the reactions are in particle physics as well as they're known and the little bump here which is shown blown up down here is the higgs boson without the best statistics that they've accumulated now the point i want to make here is that the size of this bump compared to the background is something like 1 in 10 or 1 in 20. so the uh events that we have in the higgs are only five or ten percent of the events that we take in that in that mass spin therefore if we want to study the features of the higgs there's an enormous background and that's the next step and i'm going to talk about those features a little bit okay this pictorially shows you the difference this is a collision in the lhc this is the detector schematically and all the lines are the different particles emanating and that's because so many things happen while in the lhc as i said it's much simpler these are basically two jets of particles that are the products of the higgs making a b particle and an anti-b particle and you can see that the topology is much simpler and the signal the background which i'll show you next is also very very different so this is a simulation of course not the data but this is the energy of about 120 gv the simulation for what the higgs would look like put on top of the background and so you can see at the peak this is somewhere near 300 compared to a background of about a hundred so there's the signal is two to one instead of one to ten and so if we take a band and try to analyze the features it's a totally different uh a different game so what do you want to do we want to of course accurately measure the mass of the higgs the branching ratios the width the spin the coupling and so forth let me say why the higgs is really different it's the we have a lot of particles in particle physics but the higgs is the particle that reflects on the the theoretical description of why particles have mass so it's it makes the field massive that means it behaves totally differently and has to have particular features first it has to be a zero spin particle secondly it couples to mass because it's responsible for mass other particles don't couple the mass they couple to strong interaction or weak interaction or or electromagnetic interaction but not to mass so this is unique that it cut and uh the masses and the decay rates are related to this and this is just pictorially how it couples to mass and therefore uh its features can be tested if you have a clean environment first one is is the spin zero so we want to now understand we've seen this higgs we believe it's the higgs but we want to now understand what its characteristics are and whether or not it's a simple model of the higgs or something different from that so first is to measure the quantum number show that it's been zero this turns out to be trivial to do on an electron positron machine and very very difficult except by inference on a hadron machine why because all the energy goes into the collision so we can go to threshold which i picked a graph which doesn't have the right mask but it's close and depending on how the reaction behaves off of threshold depends on the spin of the state so if the spin is zero just like in quantum mechanics you can calculate the behavior if the spin were one it would go up like this if the spin were two like this so to prove that it's been won we should see a behavior near threshold that has this kind of behavior so that's the simplest thing is to show that it's spin zero the second is the dramatic issue that the coupling should depend on mass the way to test that is to look at the coupling to the different uh particles or quarks the charm cork the tau the b cork the w the z the higgs the top so the the this should be a linear line on a log log scale if it depends on mass this would be flat if it was another particle so this is completely different behavior so it's linear but that's only the first step the second is how close to linear should it be if it's the very very simplest model of the higgs it'll be linear like this but it isn't the only model in town of what the higgs might be like i just picked one case over here so if it's simple it would fit that straight line as we went through the different particles if it's a different model i use the minimum supersymmetric model here just as an example then within 10 or 20 percent it'll be that same linear line but it'll have such significant differences depending on on that particular model so the next thing is to qualitative quantitatively measure this behavior that i showed here and asked whether it's truly linear good enough statistics to do that and that's why i show the band here or it has a shape that's somewhat different than that which will tell us whether or not the model is that the physics is somewhat different than the simplest picture of the higgs okay and just for another example of a comparison in the same energy range you can produce our heaviest quark the top cork so if you take all i've shown here is the couplings of the top quark and how well you can determine them at the lhc versus the red part the ilc so about 10 times better even though you have this weaker machine supersymmetry it's the biggest question we still have in particle physics so far at the lhc there's been many searches for supersymmetry no evidence for it which is disappointing but it doesn't rule it out at all because supersymmetry has a variety of possible parameters some of which could be see could be visible and some which wouldn't be visible so far at the lhc and the biggest goal of the coming run at the lhc the run that they're on now is to pursue more whether they see supersymmetry it may not be there or it may be there let me say what it is so we have the different constituents of nature the spin half ones which are the fundamental quarks and leptons and the carriers of the forces the photon the gluon the w and the z and there's spin one and now we have an addition we have the higgs particle that's the particles we have basically that describe particle physics first question is is there only just one higgs are there several we don't know and different there's different reasons to think there might be more so we haven't seen it but we don't know yet there may be partners of the 125 gv higgs that are higher energy so that's the first question to answer of course i showed the one already that's been zero the idea of supersymmetry is that there's a mirror set of particles that basically are these they're called the same names the neutrino becomes the higgs becomes the xeno and so forth and those are the partners basically what we've done is to make a new symmetry a predict uh what we've proposed is a new symmetry in nature that symmetrizes bosons and fermions and that's what supersymmetry is the reason it's attractive is first the qualitative thing that symmetries have always brought so much in particle physics but three reasons one is that temptingly close if we project an energy we work down here 100 gev was left and we measure things that are electromagnetic we measure things that are weak decays of particles and things that are strong if we take all the data down here and project it into much higher energy they temptingly come close to together at about 10 to the 14th or 10 to the 15th gev but they don't come together if you actually look at the accuracy of these lines they don't intersect if you were to introduce supersymmetry these basically intercept so so the idea that excluding gravity the three main forces that we study come together at super high energies and we're looking at the split of those at very low energies is a very tempting idea the unification and would be basically true if we found supersymmetry or could could be true the second is that it solves a uh theoretical problem what we call the hierarchy problem which has to do with a range of of energies that we have and how to explain that are masses that we have and the third one is that supersymmetry could be the dark matter if it's the dark matter then it's both important for particle physics and obviously for astronomy and astrophysics so it's a very tempting wonderful solution the combination of these depending on whether you're a real theorist who likes the hierarchy problem or you like the unification of forces or the combination of all these makes it the most popular idea in physics but we have no evidence that it's true okay we take that we've taken then about a decade ago all the parameters from doing studies of how we could pursue those different topics and brought together a study that went for several months and a set of parameters came out of that driven from the physics to use to then drive the parameters of a machine this is an important thing experimentally you like to not drive the parameters of an instrument you make from the instrumental things but from the science you want to do so starting from the science and knowing what you need to accomplish it you want to design a machine that'll meet that so the parameters that came out of this study are listed here i'll just say a couple words about them then i'll start showing you the machine so the parameters that came out is the machine should be adjustable in energy that's obvious uh because you want to trace the rise and fall of any one of these things the total luminosity is to get enough statistics and so that's set what this luminosity number had to be you need to be able to adjust the energies that is an added feature to be able to change the energies and not just make it at one energy and the parameters for how stable it should be and the last one is the value that you actually and it takes some work make the particles polarized and this machine should be done in a way that you can upgrade the energy or double the energy eventually so those are the parameters we've used those parameters then starting in 205 or 2006 to make a technical conceptual and then technical design of the machine so i use this picture to show the the features of the of the machine that you have to worry about to make a linear collider telling you before what the features are the main part is this long thing that's that's 30 or 50 kilometers and that's the linac and it's the most expensive but from a particle accelerator point of view all these other features which i'll talk briefly about are crucial to being able to make the thing so money wise and technology wise you have to make these long linux but we have to be able to make electrons and positrons make the optics such that we can focus them down to a very small spot and so forth so i'm going to focus on all these other elements quite a lot i'm going to briefly then take you through the machine the guts of it and the heart of it is a superconducting rf main linac these are superconducting cavities one meter long nine cells and uh made out of niobium and they uh basically look like this but there's a lot we have to make a lot of them so we have to learn how to make them in an industrial way there's a total in the machine of sixteen thousand of these cavities that we have to make in a way that are reliable and cheap so we have to learn how to have to learn how to design it so they can be made reliable and cheap and they have to have high gradient which i'll come to they they're put inside a module that looks like the magnets at cern but they're what we call cryo modules so you can cool them there's 2000 of those and then we need to be able to focus the beam and so forth so there's other elements these are not obvious how to make these these how to shape these cells so i've shown here three different shapes for these cells and basically the gradient that you can get to to accelerate particles depends on that evolution this is the natural shape that was done in 1992 and by the time we designed it we had two alternate shapes we were looking at you'll notice these shapes are are flatter in shape that makes more surface area for the same distance than you have here and the larger surface area spreads out the magnetic field compared to the electric gradient and it's the breakdown of the surface that limits you so this gives you a somewhat higher feel what our goal has been is to have a machine that runs at 35 mega volts per cavities can run at 35 million volts mega volts per meter to get to establish the length of the machine we have and and so forth and we've made a lot of cavities that easily reach that but in an industrial case it's harder of course and but we have a good test facility there's basically a smaller machine being completed at desi for a different purpose it's an x fel a free electron laser of 17 gev and has about five or seven percent as many cavities or cryo modules as we do being made in industry and having a requirement that's very similar and in fact they used our technological development to make this machine they're getting a machine and we're getting uh an existence proof of exactly how to do it all in industry so that's been done this is just i'm not going to go through these this is just to show you all the different elements besides the cavity and putting it into a cryo module where you cool it down we have to get the we have to couple one cavity to the next we have to be able to put rf in and so forth and so on so they're rather complicated inside this is the picture simplest picture i can draw the luminosity and how we achieve it uh if you look at the left that's the circular machine it has the luminosity of the the highest one i showed you has a luminosity of 5 10 to the 31 and it's done by having a fast rep rate and a certain number of particles per bunch and this is the number of bunches the parameters for the ilc are different but we make up for the ones that are low like this one the frequency uh by having a large number of bunches and uh a number of particles per bunch and we have small sizes in the end which i'm going to come to and that allows you using this formula to get the luminosity of 10 to the 34. so there's some existence of other ones in extrapolation none of which the extrapolations are so long that we shouldn't be able to achieve this there's no new problems or anything that we expect so that achieving that luminosity looks to us doable but we have to do it in a way that has the biggest challenge of the optics to somehow make sure that we can have enough collisions that these particles don't just go around each other and that's done by what we call making a very low emittance optics what does that mean admittance is an accelerator physicist term for what i would call low transverse momentum we have to get rid of all the transverse momentum so the particles are going parallel a parallel beam into a lens you can focus down to a point so we have to make basically uh get rid of the transverse momentum and then once we get rid of it we have to make sure it doesn't grow by all the non-linearities in this long system that we have and finally we have to be able to squeeze the beam so what's the requirement and this requirement is probably the toughest uh technical thing purely technical thing and that is we have to get the beam in one direction down to five nanometers which is much much smaller than any previous machine and the other direction is longer so it's a ribbon but and so we need good enough optics parallel beam to be able to focus it down to approximately five nanometers and then the two beams have a enough probability to give the luminosity that i indicated in the collisions themselves so because this is the hardest we build a rather elaborate test set up to make sure we don't run into some fundamental physics problem before we get to this small level we build it at kak laboratory in in japan and the history of how small a beam spot size we could get is shown here the optics is not the same as for the linear collider so we have to extrapolate from this but we know how to do that so this is the progress and just as we were needed the whole thing in order to convince the technical critics and the governments that this machine was feasible we had a huge earthquake in japan and that set us back a little bit uh but it's gone on since then and we're now down to 44 nanometers 44 nanometers is to be compared with our goal which was 37 nanometers very close and 37 nanometers for this configuration will give six nanometers in the ilc which has longer longer features where we can tell and that change from this to this has no error and it's just geometry okay so these are the different elements then that have to come together in the linear collider and i'm going to talk about them very quickly one by one uh first physically the the business end the machine is in one tunnel and all the klystrons and all the power supplies and everything in a separate tunnel so there's two tunnels in contrast to cern the japanese have actually changed the design to one tunnel with a barrier in between the idea is that you should be able to come into this and work on the klystrons replace them or all the technical elements while the machine's running that can't be done at cern but this machine's more complicated so we want to make sure that we don't lose a lot of time by people not being able to get access to fix things so it's a double tunnel this everything is done from the center so there's kind of a central campus in this idea where all the business end is in the center but then we send the beam all the way out and accelerate it on both ends one end being electron one end positrons so all the things i'll talk about could be in a laboratory that's uh a few kilometers by a few kilometers and that includes the electron source the positron source the delivery system for the beam itself which has to make these very small spot sizes the interaction region where the detectors go what i call damping rings which i'll tell you what they are in a second and all of this is together rather complicated because they're all together in the same area but it means that you have a central laboratory where you can work this is the damping ring i'm not going to go through the details of the damping ring but i'm going to tell you what it's for we have to get rid of the transverse components of the beam the way you do that is to have these elements that are shown here called wigglers and the wiggler basically wiggles the the electrons they radiate photons in that process they radiate away the preferentially the energy that's transfers so the way we dampen the transverse components is to have this so-called damping ring so that's the trick there the ring itself is very similar to third generation light sources uh we have these extra wigglers to get rid of the they use wigglers effect effectively that to radiate photons for physics but otherwise the machine is pretty similar to that it's three stories high we have the electron ring over the positron ring and we have two positron rings to have enough particles second is to make enough positrons to make positrons in this machine electrons are easy you strip those off of things but the positrons are basically harder to make we make those by running electrons up to high energy then running them into a target where they make photons which convert to make electron positron pairs grab the positrons and accelerate them afterwards so it's a rather complicated system which i won't go through here and you have to pick the energy such that you capture you can both capture the positrons afterwards and you produce enough positrons and that tends to be not so far from the total energy of the machine so you basically have to bring the electrons up to three quarters or the whole energy of the machine then run them into a target so we do every other bunch one of the bunches to make positrons one of the bunches to use as electrons this is the polarized electron source this is not so difficult compared to what's done in other accelerators except we want the electrons to be polarized which limits the choices of what kind of gun and what kind of scattering we use i don't have time to really go through that but we make sure the electrons are polarized the last that i want to show i think it's the last before the detectors is a rather long element which is you come out of these two linex and now we want to bring the beam down to a very small spot size so even if we kept all the optics very carefully right we still have to bend particles bring them together and so forth and we can't spoil this perfectly parallel beam from coming together into this very small beam spot size that turns out to be a rather long and tedious process to do it in a way that comes down to a small beam spot size and you'll notice that the total length is a few kilometers because if we bend the particles too much they radiate so it's very soft so they don't radiate and then we have all kinds of ways of getting rid of back ground particles that's these collimators and to bring them into a final focus this is the schematically then what happens it comes in then on one side as positrons on the other side as electrons and then we have a surrounding detector which has two main features one is that it tracks every outgoing charged particle and its momentum in a big magnet and the second is it identifies particles from each other it identifies particles from each other in different kinds of calorimeters and it basically tracks them in very accurate tracking usually silicon strip trackers and this is typical of the experiments that are already done at cern but with more emphasis on better resolution in in this case there's a tradition in particle physics to have two detectors to be able to check anything you have and have different systematics so there's two cern detectors in our case it's too expensive to build two different areas so instead we have what's called a push pull system so in series one detector can roll onto the beam the other one off the beam and you run for some time with one and sometime with the other the resolution that we need and i just want to give you the feeling for this is considerably better than what's achieved in the lhc detectors this is the pixel size how much smaller roughly a factor of 10 30 in some cases that the material has to be less so we don't scatter and lose particles or convert them and that we do better calorimetry than what's traditionally done in particle physics all of those have been worked on very intensively in r d program not by accelerator physicist but particle physicists and just as an example this is the production of the higgs particle and what it would look like here it is what it would look like with better resolution compared to the present kind of resolution that you get on the lhc so that's the motivation and pictorially we want to be able to separate particles which now are not separated in the lhc this is lhc type resolution into separate jets and those again in test beams have been developed okay this is the site that has been chosen by the japanese physicists geologists and government to put this machine it's in japan about four hours north of tokyo in an area called kitakami it's in the what they call the mountains but it's not really mountains it's foothills they go enough into the mountains for this proposed site so that the underlying geology is granite which the japanese like because granite's very very stable and they've developed the technology to tunnel and granite despite its hardness and so the tunnel is granite and it basically then doesn't have to be stabilized it's 50 kilometers long at the site you can see you can't go further here you'd be at the sea uh it's 300 meters above sea level but it's 100 meters below the ground so it's not going to be hurt by a disaster like happened before in japan and being underground there's very little shaking so it's very stable i just want to spend the last three minutes that i have on what other machines are being talked about the chinese are actually talking about building the next generation proton machine bigger than the lhc and something like 75 kilometers around this is a picture of it it's just a big machine if they built this machine they could start by using because it's bigger by using e plus e minus in the machine and have high enough energy which they didn't have at lab to study the higgs so if the japanese machine isn't built they could use it for that and then convert it to a high energy proton machine this is in its very early stages of design they haven't yet solved the problem that if you have one turn where you bring the particles together and they disrupt each other and when it comes around again they're useful and can be focused again but it that's probably solvable so it's in a it's in a design phase and lastly i just want to mention before i stop is this the end of particle physics what i've shown you the ability to make these accelerators i think probably not but let me just tell you why we don't know for sure but making accelerators like we're talking about we're near the last generation either the ilc or maybe a machine like i just talked about are there other techniques where we might be able to go to higher energies and make machines that could go to higher energy if you think about the problem what limits us in the present generation of machines and all machines we've had is materials in the case of magnets the field that we can get in the magnets is limited by the by the materials they're made out of if we talk about cavities we may do better than niobium but not much we're limited by when the surface breaks down and how much we can put on it so is there a way to get rid of materials that's really the goal the need if you were to go to another generation someday and there is a scheme and it may work but it's very early and that is to use eliminate materials and use a plasma that you excite and run particles into the plasma in the way that we've talked about so our machine looks like this and you can make a plasma cavity that looks like this put a plasma in and excite the plasma with either a beam of particles or with lasers and uh what's been done and demonstrated is promising this they managed at slack to make a small one meter long cavity that took a machine that's two miles long and accelerates particles up to 40 gv and in one meter they doubled the energy but only for a few particles so this is the 40 gv and a few of them getting up to as high as 80. but the fact they can double it of course to make a viable machine you have to bring them all up or most of them up and not not but they have been able to get huge accelerations in a very short distance with plasmas where you're not limited by them by the materials the second is can you take plasma beams and focus them at all and there's been work most recently in berkeley where they've managed to at low energies focus beams uh made in a plasma to let less than one degree which is not as small as we do for high energy accelerators but is reasonable and reduce the energy spread to a few percent so you don't have this long tail that i showed and so that's promising as well the work that's going on now is to do it on a bigger scale and to try to do this i would say it's tens of years away maybe 50 or 40 or 30 or something but my conclusion is that there could be if if the physics demands it the ability to go to yet higher energy and accelerator so let me summarize and then i'm done the international linear collider is being considered in japan it's got very strong science motivation which i showed you the the technology is very mature it's been well reviewed everywhere and the question is whether the japanese government and the physics community really wants to take it on if it's finished it would be like 2025. there's a couple alternatives that i didn't talk about other options there's a way to make an accelerator like the linear collider but not with superconducting technology but instead by a different technology which i won't describe it is a very because it's not superconducting it's very power hungry and so power consumption becomes a big issue if we're going to do that another idea is to start with muons and make a muon collider which is the same physics as an electron collider that's a very intriguing idea but has an enormous number of issues to actually make pie mesons that make muons capture them and actually focus them into this kind of beam and then i mentioned the chinese large machine and the final thing is the possibility of either laser driven or beam driven plasma weight field accelerators and with that i'll stop thank you you

Channel: World Science U

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Keywords: Barry Barish, Higgs, Higgs Boson, LHC, god particle, particle physics, dark matter, Standard Model, black holes, superstring theory, supersymmetry, quantum gravity, Einstein, extra dimensions of space, Bekenstein, Calabi-Yau, holographic worlds, multiple universes, supersymmetric quantum field theories, mathematical physics, Superstring theory, best science talks, New York City, World, Science, Festival, 2020

Id: -ulbZ8FgTyg

Length: 61min 0sec (3660 seconds)

Published: Thu Oct 01 2020