What can we learn by smashing muons together?

00:00:07
Speaker 1: People have wanted to know the answer to the question what is the universe made of? Since we've been asking questions about anything, it seems a reasonable thing to want to know the answer to what am I made of? What are you made of? What are kittens made of? Lava or stars? Around us? We see an incredible complexity. We want to know if there's a simple explanation for this glorious universe. Does it have some kind of basic bits, a small number of which interact in complex ways so that from their toing and froing emerges all of the complexity of chemistry and biology. We've made some good progress on that question, and we now know that you and I and kittens are made of three kinds of particles, of quarks, down quarks, and electrons, and in basically the same proportion. What makes you you and what may lava lava is not the bits they're made of, but how they're put together. You are your arrangement of particles. And we figured most of that out by doing something pretty simple. Take this stuff around us, usually electrons or protons, and smash you together to study what comes out, and we found all sorts of exotic matter, muons, other quarks, higgs, bosons, stuff that isn't part of the atom. But what if we flipped the script and smashed some of that exotic matter together? What could come out? What might we learn? How could we even do that? We're going to dive into all that today on the episode Welcome to Daniel and Kelly's extraordinarily smashy Universe.

00:01:58
Speaker 2: Hello, Kelly Smith study parasites and space. And while Daniel gets away with smashing particles into each other all day long, I feel like I would get in trouble if I smash fish into each other all day long. So I feel like maybe there's a double standard.

00:02:11
Speaker 1: Here, Kelly. I don't think fish need you to smash I think they do it all by themselves out there in the ocean.

00:02:20
Speaker 2: I mean, they're not super smart, but they're not that dumb. Daniel.

00:02:24
Speaker 1: Hi, I'm Daniel. I'm a particle physicist, and I love smashing particles. But I'll smash just about anything together.

00:02:30
Speaker 2: Oh and you know, I hope this goes without saying, but I don't actually want to smash fish together. I like fish a lot, So Daniel. Today, I want to know what is the most surprising thing about working at Cern.

00:02:44
Speaker 1: I think one of the most surprising things about working at Cerne is the natural beauty of the environment. There you are in this valley surrounded by incredible mountains. You have like the Alps on one side, you have the Zura on the other side, you have the sin on another side, so it's already gorgeous. And then the valley is mostly filled with vineyards and sunflower fields. So summers i was there, I was biking to work through vineyards and then fields of like millions and millions of sunflowers. It's just really astonishingly incredible setting. And so I love sending students there because of course their minds are blown by the science but also by the beautiful nature.

00:03:22
Speaker 2: And then you go inside and it's physicists wearing socks and sandals and they kind of stink, and the juxtaposition is just absolutely overwhelming and surprising. Is that is that where this was going? No, it's just no, Kelly, No.

00:03:37
Speaker 1: Yes, exactly. No, it's a wonderful surprise to bonus. When you go to Cern, you're there for the science. Plus also it's in one of the most beautiful places in the world. So yay yay.

00:03:47
Speaker 2: That does sound amazing, and I love physicists and my husband wears socks and sandals, so I have learned to live with that.

00:03:55
Speaker 1: Well, I have a pop quiz question for you, Kelly.

00:03:57
Speaker 2: Oh oh okay, what is.

00:03:58
Speaker 1: Your best off the cuff prinunciation of the particle we're talking about today?

00:04:02
Speaker 3: Uh?

00:04:03
Speaker 2: Oh uh mwon. Isn't that right? Mwon? That's one right, everybody is shot everyone. I could have maybe mealon, I could try to make some cat jokes, but no, I got this one where you've probably said this particle many times on the show, and I guess.

00:04:18
Speaker 1: So yeah, yeah, because the most common mispronunciation is MoU on, like what a cow might say, but it's mew on, like the Greek letter mew.

00:04:28
Speaker 2: All right, well, so here here is getting into my head. When I hear a wrong pronunciation, I start getting really fixated on it because I don't want to say that, and so I will probably say muon at some point in the show now because my brain sabotages me at every corner. So on today's show, we're talking about smashing muons together.

00:04:51
Speaker 1: Absolutely, we are we willing to understand the nature of the universe, and we will do just about anything to get there, from building ten billion dollar particle collis in incredible natural settings to inviting aliens to come and tell us the secrets of the universe. We are just desperate to know here on the show. But you might be wondering, why would anybody smash muans together? Don't we have enough other stuff to smash together? So that's today's topic. Before we dive in, I went out there and asked our listeners what they thought we could learn from smashing muons together. Here's what folks had to say.

00:05:26
Speaker 4: And then we could learn what other sub atomic particles muons decay into, and that could help us better understand the fundamental building blocks of matter in the universe.

00:05:35
Speaker 1: Fractions of.

00:05:38
Speaker 3: Particles, just the importance of spending mutual activity time together. And oh wait, you've been smashing them into each other. I'd say that's probably tetriquarks. Then we could underlock much larger energies.

00:05:53
Speaker 1: We could learn what's inside.

00:05:54
Speaker 3: Of them, create a kind of a some sort of exotic state of matter.

00:06:00
Speaker 1: Are mouons something that cows emit? If there were two back to back and the emitted moons and they collided, what a smell? Oh my?

00:06:11
Speaker 2: We could learn about the arc energy.

00:06:15
Speaker 1: Release some massive type of energy. This could be used for possible applications for nuclear fusion.

00:06:21
Speaker 3: Maybe it could be the best way to make chocolate.

00:06:25
Speaker 4: Why we could learn the secrets of the universe and why. But seriously, I think it would be interesting to delve into a heavy electron essentially and maybe find out if there's something below that, if it's made of something.

00:06:40
Speaker 1: The constituents and why they decay into neutrinos and anti neutrinos. So smashing luons is a new band that's taking over from Smashing pumpkins.

00:06:51
Speaker 3: So first of all, you spell moons wrong, and by smashing moons together you would learn how to become very bad as supervidin.

00:07:00
Speaker 5: So it seems like because muons have greater mastering electrons but the same charge, it should be easier for us to see evidence of gravitational attraction between them.

00:07:12
Speaker 2: We could learn what happens if you smash muons together.

00:07:15
Speaker 3: See what makes up these particles, and maybe get a better idea of how the universe is made up.

00:07:22
Speaker 2: Amazing answers, And if you would like to be an extraordinary who shares their thoughts with us, go ahead and write us at questions at Daniel and Kelly dot org and will put you on our question list.

00:07:33
Speaker 1: That's right, and these are some hilarious answers. I'd love to see the band Smashing Muons performed live.

00:07:40
Speaker 2: I like the one that said you spelled moons wrong exactly.

00:07:44
Speaker 1: I would love to build a moon collider. Wow, that would be amazing. We would learn so much.

00:07:49
Speaker 2: Yeah. No, Daniel's always willing to risk humanity for the sake of learning something about physics. I am not on board.

00:07:56
Speaker 1: I think the answer about gravity was super interesting because because they're right that muons have more mass, and it's tempting to think, ooh, does that mean that we could use them to study gravity? But remember gravity is crazy week like ten to the thirty times weaker than other forces. So even though muons have more mass, you're not going to see their gravitational attraction.

00:08:17
Speaker 5: Boo.

00:08:18
Speaker 2: You all just haven't figured out a way to really address that question.

00:08:21
Speaker 1: Have you. No. I have figured it out. I just haven't gotten the funds for you to keep writing proposals for my black hole collider and to keep coming back saying no.

00:08:31
Speaker 2: Yeah, good luck, good luck. I don't think anybody should give you like a species annihilating tool because you might use it.

00:08:38
Speaker 1: But all right, I will one hundred percent use it.

00:08:41
Speaker 2: Yes, okay, nobody fun Daniel. All right, let's start by talking a little bit about like how we go about smashing particles together in a controlled way, So like why do we build particle smashing colliders and how do we build them?

00:08:57
Speaker 1: Yeah, well, why do we build them? Because because they're there?

00:09:00
Speaker 2: No, come on, do you know that he died summoning Everest?

00:09:04
Speaker 1: Oh boy? Yeah, right, Well I'm willing to die to learn the secrets of the universe. Yes, I will press the big red button on that crazy collider. No, we are not just here to ant humanity. We are here to learn the secrets of the universe. And there's a lot of unanswered questions about particle physics that we think building particle smashers can help us answer. So, for example, we know that the world around us is made out of protons and neutrons and electrons. Inside those protons and electrons are quarks. So we have the upcork, the down cork, and the electron make up everything we know and love. And what you had for lunch today and what you're going to have for lunch tomorrow and the next day and basically forever. But we also know that those three particles can't explain everything that's out there in the universe. But there are other exotic states that matter out there, Like the electron has its heavy cousin, the muon and an even heavier cousin the tao. The quarks have heavy cusin as well, charm and strange and top and bottom, and then there's three neutrinos. So we have this periodic table of the fundamental particles, has these twelve particles, and only three of which are needed to make up the matter that we know and love and have for lunch every day. And so we have lots of questions about that table, like why are there so many particles, Why there's such a big range of masses. What's the relationship between the electron and the quarks? Their electric charges balance very very nicely to make hydrogen, but nobody really understands why. So there's a lot of unanswered questions about particle physics we'd love to answer, and a particle collider is a great.

00:10:37
Speaker 2: Way to do that, all right, So muons are like electrons right after the Thanksgiving Christmas season, how what is it that makes muons heavier than electrons?

00:10:51
Speaker 1: Yeah, great question, So muons are not electrons that got heavier. Electrons and muons are very very similar, so we categorize them in the same way, or of the way you might like group carbon and silicon together. They have a lot of similar properties. They're in the same part of periodic table, but they're not the same. A muon is like an electron in that it has the same electric charge, right, they're both charged minus one, and it doesn't feel the strong force, so it's very similar there, and it's the same weak force charges, so that's all very similar. But it has more mass, and you ask why does it have more mass? Well, the Higgs boson gives it more mass, so masses of these particles come from their interactions with the Higgs boson. So the muon interacts with the Higgs more than the electron does and gets more mass. That's kind of an answer to the question because you say, well, why do you have more mass because you interact more with the Higgs. But it sort of kicks the question down the road to like, Okay, why does the muon interact with the Higgs more? We don't know that's just a number we've measured in the universe, and we don't have any explanation for it. So why is the muon heavier? We don't know. Why is it how even heavier? We don't know. Why is the top super duper crazy heavy compared to all these particles. We don't know. These are questions we don't have answers to. We're just like looking at the pattern of the masses and going, hmmm, there's probably something going on here, And in one hundred years people will look back and be like, it was so obvious yet idiots, Come on, I would have won a Nobel Prize if I was a physicist in twenty twenty five. But you know, science is not linear. It's not just like some path in your video game. When you're standing at the forefront of human ignorance, it's not obvious to know what is the right way forward.

00:12:26
Speaker 2: So in a previous episode, I remember you telling us that we don't know if electrons are fundamental or not because you all have like tried to break it apart a bunch of different ways and none of them have worked. Do we think they will break apart if you smash them together?

00:12:38
Speaker 1: We certainly hope. So we don't know. You're right, We have not seen inside the electron, and we don't know if smashing me want together will reveal their inner bits. It's one reason we might want to do that, and it's a deeper question, like what's inside any of these particles quarks and electrons. We suspect that the answer we have today these quarks and electrons and other kinds of leftons is not the final answer. That these things are like the periodic table, that all their properties are emergent phenomena from the rearrangements of like smaller bits that do their thing in different ways, and that's why this looks like an electron, and if you rearrange them, or if they are in a different energy state, it looks like a muon. One example of that is string theory. String theory says all of these are just strings vibrating in different ways. It's really just one fundamental thing. And when you zoom out and you see that string behaving in different ways, it looks like different particles. But of course there's no evidence for string theory or anything inside these particles. But that's an example of what we'd like to know. The point I want to make is that there are burning questions about the nature of matter and energy in space and time, and we hope to answer these. So not just what's inside these particles, but like, why is our universe made of these particles and not the antimatter version of these particles? The muon has an anti muon, the quarks have anti quarks? Why are we all made out of matter? And most of the universe seems to be made out of matter, or even more broadly, like most of the universe is not actually made out of matter. It's made out of dark matter, and we have no idea what that is. And so these are the unsolved questions in particle physics we'd love to get answers to, and if we could just download them from aliens, that would be great. But colliders are a great way to get answers to these kinds of questions.

00:14:17
Speaker 2: Okay, so then let's dig into how colliders work.

00:14:20
Speaker 1: So you might be wondering, like, how does a collider give you an answer to these questions? Just smash particles together? How does that tell you about the nature of the universe? Right, Well, the cool thing about colliders is that they can create new particles or reveal what's inside the particles that we already know. So, for example, when you smash these particles together really high energy, you're giving the universe sort of a big budget. You're saying, here's a bunch of energy all in one place. Make whatever you can make. And you know, the time in the universe that we live now is when the universe is very dilute, very old and cold. There's not a lot of energy around. It's all very spread out. Back in the early days of the universe, you know, the first few seconds, the first few hundred thousands of years, there was a lot of energy density, and so the universe could do basically everything that it was capable of because there was always enough energy around. It could make top quarks, it can make Higgs bosons, it can make anything that was on its menu. These days, it can only make really low energy stuff like electrons and protons. So what you're doing when you smash particles together is you sort of recreate the early moments of the universe when there was enough energy to do everything. You know, before all of the budget had been spent. And so you smash the particles together, and then the universe rolls the quantum die and says, hmm, what can I make with my energy budget? I'm gonna pick from the list. And so if you smash the particles together often enough, you'll see everything on the list. That's really amazing that you can like explore what's possible in the universe, what's on the sort of nature's menu of ideas of what the universe is capable of doing, even if you don't know that it exists in advance and you have no idea how to put it together. You just smash these particles together like a bunch of idiots, and eventually the secrets of the universe just like pop out.

00:16:03
Speaker 2: All right. Well, so I'm old and cold and low energy, but probably it wouldn't be good to put me in a particle collider. I'm guessing have you tried it?

00:16:12
Speaker 1: I mean, geez, don't be so closed.

00:16:13
Speaker 2: Minded, co I mean, aren't there. So my daughter had a tour of surd and I'm pretty sure that they were like signs everywhere being like, don't get in the collider.

00:16:21
Speaker 1: Yeah, And we had a whole episode about that poor Russian guy and leaned into the beam and it's not a good idea.

00:16:28
Speaker 2: Yeah.

00:16:28
Speaker 1: I mean, I'm saying, don't get collide with a beam of particles, but with a beam of Kelly's who knows.

00:16:33
Speaker 2: Could be fun? Could be fun. Okay, So then how do you actually break open a particle?

00:16:39
Speaker 1: Yeah, exactly. So one way to discover a new particle is you like smash the particles together and they turn into a blob of energy and boop, some like a Higgs boson pops out or something new or dark matter or whatever, and you flesh out your table. It gives you more context. Another way to make a discovery is to crack open one of the things you already know and say, oh, look inside the proton, there are three little bit we call quarks, right, And so the way to do that is to exceed the energy of the bonds holding the particle together. So proton is not just like three quarks near each other. It's three quarks tied very tightly together with gluons. It's like really intensely bound together. But those bonds have some finite energy. If you're beam, if you're like, shoot an electron at that proton, and the electron has more energy than the bonds holding the quarks together than those gluons have. Then you're going to break that proton apart and you're going to see those quarks fly out. It's sort of like if you bounce a ball against the wall very gently. What happens, Well, it just bounces back off. Right, you haven't put enough energy in to separate the bonds in the wall. But if you build a super fast gun and shoot your ball at the wall, it's going to crack the wall open. Right, you're going to see what's inside the wall or behind it. It's the same thing with particles. If you shoot them together with less energy than they have in their bonds, then they're going to act as if they're fundamental because the bonds are going to hold them together, going to see what's inside. But if you can crank the energy up so it's greater than those bonds, then you can shatter those particles and see what's inside. And that's how we saw what was inside the proton. We actually shot an electron at the proton and we saw it bounce off of the little dots inside the proton.

00:18:16
Speaker 2: So when we shot an electron at the proton and gave it enough energy where we could see it like bouncing off the quarks. Did we have a theoretical expectation for when we should be able to find the quarks? And do we have something similar for electrons and muons?

00:18:35
Speaker 1: A great question. So the context there was exciting because we already had an idea for what was inside the proton. We had all these particles that nobody could explain. It was called the particle zoo. Basically, every time you turned on a collider, you discovered some new particle. There are so many of them, is a wonderful time to be an experimentalist. But then the theorist sort of organized them and categorized them and said, oh, you know, this would make a lot of sense if all of these were made out of three different bits. They only knew about three different quarks back then, and that would explain all of these particles. And some people were like, yeah, that's cool, but it's just like mathematical chicanery. It's not real. And other people are like, no, no, no, they're real. They're really in there. So they sort of knew to look for them and what they were looking for, and roughly the scale of the energy you would need. Today, we do not know what might be inside the electron or the muon or the quarks if there are strings that you need like a solar system sized collider to see them, or maybe even bigger. But there are other theories about what might be inside them, all various different kinds of theories, and so it could be that it's like just around the corner they were about to crack open the electron, or it could be that like, yeah, we need a solar system sized collider, so we don't have a good guess about when we might see these things.

00:19:48
Speaker 2: Interesting, Okay, so it sounds like you'all take the same particles and you smash them together over and over and over again, and so it feels like, probably you just need to do that for like five minutes and then and you analyze your data. But y'all have been at it for a really long time, and so why do you keep doing it?

00:20:08
Speaker 1: That would be amazing, And you know, there are some examples of that, like when they turn on Lego to see gravitational waves. They expected it to take years to see black hole collisions, and they saw one like the next day, and they were like, what are we fool in ourselves? This is a joke, And we didn't know when we turned on the collider, what we would see because this is uncharted territory. Nobody had ever collided particles that this energy before, and we could have had like crazy pink elephants jump out right. But the amazing thing about these colliders is how the universe determines what comes out of each collision, like it really is random, because we try our best to create exactly the same collision over and over and over again. And if you have in your minds like balls, like ping pong balls colliding, you know that if you do that over and over again and exactly the same initial conditions, you'll get exactly the same outputs. You can predict exactly where they're going to go at what angle energy. You can't do that with quantum particles because quantum mechanics is deterministic in a different way than classical mechanics is it only determines the probability of various things happening, not the actual events. So every time you collide particles, you draw from a probability distribution and say, well, what are we doing today? All right, we're doing it again, how about this time? And so you get different outcomes every time you collide. The particles, which one hand might seem frustrating, like hmm, you don't have as much of a handle, you can't predict exactly what's going to happen. But on the other hand, this is exactly what allows you to explore the universe because you don't have to know what's in that probability distribution. And the thing about that distribution is some things are super duperor likely, like two protons come in, two protons come out, that's like ninety nine percent of collisions, but very rarely, like once in a trillion collisions you get a Higgs boson, And we don't know if the tails of those distributions have super duper rare things, like maybe every quadrillion collisions you get something bizarre and crazy nobody's ever seen before. The projects right now is to run the collider really fast, like lots of collisions, really long, to look for really really rare stuff, stuff the universe only occasionally makes if you ask like a zillion times.

00:22:12
Speaker 2: So how do you know when to stop then? Because at some point if you haven't gotten a new result in like a decade, and the funders are like, really, we're going to keep paying for this, Like how do you like, do you have some way of saying like, Okay, we've done it enough, it's time to move on to something else.

00:22:29
Speaker 1: You have put your finger on the button right there, Kelly. Yeah, it's diminishing returns, Like the longer you run your collider, the more you can set statistical limits on what can't be there. Like, if there was something big there that comes up pretty often, we would have seen it already, so we can say that that doesn't exist. But there could always be something weird and more rare than you could have seen that you might be able to capture if you just run longer and longer. But it is diminishing returns, and eventually the mood shifts and people say, well, maybe we should build a bigger collider, higher energy, rather than to keep running the same one longer and longer. Or maybe people decide this isn't worth the money. We're gonna go off and do a different kind of science instead.

00:23:09
Speaker 2: All right, well, let's take a break and when we get back, we'll talk a bit more about how we get these particles moving so fast and how these colliders work. All right, we are back and we're talking about how colliders work. We've talked about smashing particles together. I've managed to pronounce mew on right almost the entire show. I'm proud of me, You're proud of me. So Daniel tell us more about how these colliders work.

00:23:51
Speaker 1: So colliders have a few jobs to get them up to high speed. What they have to do is push and bend right. So most of the clutters are talking come out today are circular colliders, which gives you opportunities to push the particles again and again and again. It's like when your kid is on a swing, right, you don't just give them one big push and then they're swinging, and you start off slowly and you give them lots of gentle taps and then eventually they're swinging like crazy. It's the same story with colliders. You have particles that have an electric charge. They're moving in a circle, and you have alternating pushes and bends. So you have a little linear accelerator that pushes the particles a little bit faster, and then a magnet which bends them back in a circle, and then a little pusher and then a bender, and then a pusher and then a bender. So the pushers are rf cavities are chambers filled with electromagnetic waves that the particles basically surf and gather some of that energy and come out faster. It's like a fancy version of just having an electric field that accelerates the particle. It's an oscillating electric field that moves with the particle so it can continue to push it the whole way, and you can have like bunches of particles in there, so it's a fancy version of that. And then you bend them so that they keep going in a surfa.

00:25:00
Speaker 2: First of all, the RF cavities sound awesome. I don't think I had heard of that before. But so if you are trying to work with protons, neutrons, electrons, like they've got all these different charges and you're using magnets to try to make them bend, does that mean that you're going to like lose something like neutrons around the corner because they don't respond to the magnets and they smash into the wall. Like what's the limitation of the magnets.

00:25:22
Speaker 1: You can't build a circular particle collider neutrons because you can't accelerate them and you can't bend them. Okay, so you can only really work with charged particles. You can make a neutron beam if you have something else which decays into neutrons, but you can't like direct it or shape it. It's frustrating to work with neutrons because they're neutral, But we can do it for electrons. So we could do it for protons. But you need a different kind of accelerator for protons or for electrons because they're very different masses. Electrons very very low mass, protons relatively high mass, and so you need an accelerator tuned specifically to the particle. You can't put electrons and protons in the same accelerator.

00:26:00
Speaker 2: It okay.

00:26:00
Speaker 1: And at the Large Hadron Collider, we use fancy technology to make these magnets as strong as possible because you either need a really big ring so your bending is gentle, or you need a strong ring with powerful bending, and then you need powerful magnets to do that bending. And so the most powerful magnets we use are super conducting magnets, and they use like ninety six tons of super fluid helium, which cools it all down to like two kelvin. For a very strong magnetic field, it's like seven tesla. And this is very cool, but it also means haha, very cool, But it also means that anytime you want to fix it, you have to warm up the magnets and you do it gradually. It takes like weeks and weeks, and then when you repair it and then you got to cool it down again, it takes weeks and weeks and weeks. So it's awesome to have them be super cool, but it would be really awesome to have room temperature superconducting magnets.

00:26:49
Speaker 2: So was that like space constraint, It wasn't possible to build a big enough one where they could slowly be bent, and you had to do it a little bit more of a harder bend.

00:26:58
Speaker 1: Yes, surn is already thirty three kilometers around, Like that's a big tunnel. Yeah, and so yeah, you can build a bigger one, but then the tunnel becomes crazy expensive, so nobody wants to build a new tunnel these days. A lot of the conversations about colliders are like what can we fit inside existing tunnels or also how can we make tunnels cheaper? Right, So lots of different people working in different directions, and in most colliders you actually have two accelerators in the same tunnel. So, for example, the tevatron, we had a proton accelerator going one way and the anti protons going the other way.

00:27:34
Speaker 2: Because you wanted them to run into each other.

00:27:36
Speaker 1: Yeah, you want them to run into each other. And the large Hadron collider where protons going one way and protons going the other way at the same time because you want colliding beams. And so the large Chandron collider's actually two accelerators in the same tunnel. It's crazy.

00:27:49
Speaker 2: So if you send a proton and an anti proton and opposite directions to smash into each other, is that a big explosion, she says hopefully.

00:28:00
Speaker 1: Yeah. In fact, that's what the tepatron collider was, and the SPS before the super proton signatron that discovered the WZ bosons. They collided protons and anti protons. And there's a lot of different choices to make here about what particles to use and what particles to collide. There's some pros and cons here. So electrons are really nice to use because electrons appear to be fundamental, right, They don't have stuff inside of them, So you can like accelerate the electron up to a certain energy and you know, all that energy is going to go into the collision with the anti electron, right, It's very clean in that way. Also, because the electrons don't feel the strong force and so the interaction is limited, you don't get like crazy gluons everywhere, and so collisions with electrons in them are very clean. They're easy to understand, you can control the energy. There's not a lot of messy stuff in there. But because electrons have kind of a low mass, when they go around the corner, they have to radiate a lot of energy, and so electrons moving in an accelerator will radiate a lot of photons, which means that it's hard to get them up to really high energy. So electron colliders are good for precision measurements. You want to like study something you already know is there, create it lots of times in a really clean environment so you can study it in gory detail and measure its properties. Good to use electrons for your collisions, but if you want to explore a new energy range, you want to get to the highest energy you can, then you use protons.

00:29:26
Speaker 2: So my brain today is kind of stuck on that conversation we had about whether or not electrons are fundamental. Does the fact that they work so well for these purposes suggest they really are fundamental? And why are we even still looking for a way to break apart the electron? Or it's just for the speeds we're talking about assuming their fundamental works because we know they're fundamental when you're working with these particular kinds of energies. So even if we're wrong about it being fundamental, we can still go forward with this experiment.

00:29:55
Speaker 1: Yeah, it's the second one exactly. We don't know if they're fundamental. They appear to be fundam mental at our energy level, and so we can take advantage of that, the fact that they don't crack open, that they're very simple, that the whole electron is interacting with the whole positron. In contrast, protons are much messier because they're not fundamental, and we can crack them open. So what happens when you collide to protons You don't really collid two protons At those energies. The protons aren't even bound together. The energy of the bonds is almost zero compared to the energy of the protons, So you're colliding a bag of quarks with another bag of quarks, so the quarks interact with each other, or all the gluons inside the bag interact with each other, and so you can sometimes get like a bunch of different interactions all at the same time. It's kind of a mess. And because they feel the strong force every time they interact, they're gluons everywhere. It's just like sprays of gluons all over the place. And so the fact that protons are not fundamental is one reason why they're so messy to collide. So you might think, well, why does anybody ever collide protons. Well, protons have a lot more mass than the electron, so when they go around the corner, they don't radiate as much energy, fewer photons, and so you can get protons up to higher mass then you can get electrons. So if you want to explore a new energy range, create stuff that hasn't existed before, protons are the way to go because they cover a big energy range. Like you accelerate protons up to seven thousand gigle electron volts for example, the quarks inside them are interacting at a lower energy because those quarks have a fraction of that proton's energy, So you get interactions at many, many different energies, whereas with the electrons, you collide them at a certain energy. You know, every collision has exactly the same energy because you're putting all that energy into the electron and it goes into the collision protons. You have these bags and what interacts with what you can't control that. How much energy they have, you can't control that. It's a big mess, but it's a very very high energy, and so if there is something new in there, you're probably going.

00:31:51
Speaker 3: To see it.

00:31:52
Speaker 2: Okay, So protons and neutrons are made up of up and down quarks, and gluons are the charges that hold those quarks together.

00:32:00
Speaker 1: Gluons are the particles that carry the strong force, and they are also charged under the strong force, So they're very very messy. Gluons are to the quarks the way like photons are to electrons.

00:32:11
Speaker 2: All right, So protons high energy, messy, electrons low energy clean Exactly. How have the for the particle accelerators that we've made so far? How have we sort of split out our interest in protons and electrons?

00:32:26
Speaker 1: Yeah, so we've sort of been going back and forth. Some discoveries have been made at electron positron machines. Like the discovery of the Jape side particle was at an E plus minus machine at Slack. That's actually a rare example of a discovery at an eplus minus machine because they had to know exactly what energy to tune that machine to make that particle, because all the energy goes into the electrons. And if you remember, there's a whole controversy about like how they knew how to tune it, and they discovered exactly how to tune it like one day before their competitors were about to announce the discovery of the Jape side and so there's a big scandal there. Go check out that episode.

00:33:03
Speaker 2: So when you say e pluss, is that an electron and an anti electron?

00:33:07
Speaker 3: M Okay, got it?

00:33:08
Speaker 1: Yeah exactly. So you smash electrons and anti electrons together, they annihilate into like a photon or something, which turns into in this case, a charm and anti charm, and that's what the japside particle is.

00:33:20
Speaker 2: All right, awesome.

00:33:21
Speaker 1: So that was at Slack and then CERN built the super proton sygnotron, which collides protons with anti protons like antimatter. Again, we're not just talking about like scooping stuff up from around the Earth and smashing it together. I have to make anti particles, just like they did at Slack when they used positrons.

00:33:39
Speaker 2: That sounds like a lot of work.

00:33:40
Speaker 1: It is a lot of work. And they use the same strategy for the next accelerator, which is the tevatron. This is the one outside Chicago where I got my PhD. This collides protons and antiprotons and it discovered the top quark.

00:33:52
Speaker 2: Way to go tevotron people, did you discover the top quark?

00:33:55
Speaker 4: Daniel?

00:33:55
Speaker 2: In particular, I.

00:33:56
Speaker 1: Did not discover the top cork. That was in nineteen ninety five and I was in college. I do remember my particle physics professor announcing the discovery in class one day, and I got kind of chills. I was like, ooh, this feels like a momentous occasion. And it was because in particle physics you don't discover stuff very often anymore. It's like every ten to twenty years, and so like that was a moment.

00:34:17
Speaker 2: For sure, very cool And did that make you want to go to grad school?

00:34:20
Speaker 1: It did?

00:34:21
Speaker 2: It?

00:34:21
Speaker 1: Maybe like ooh, maybe the next one's around the corner. I want to get involved.

00:34:25
Speaker 2: Yeah, very cool, little did you know?

00:34:27
Speaker 1: Yeah, exactly. And after the Temperatron they built a large electron positron colider at CERM. This one didn't discover any new particles. It was an E plus minus machine, but it was really good for measuring the W and the Z and the top really really precisely. And because of those measurements, we were very confident that the Higgs existed. Like because of the properties of those particles, we could sort of triangulate what the Higgs might be doing because the Higgs is involved in all those particles. So even though we hadn't seen the Higgs directly, we could sort of like into it or deduce what the Higgs had to be like from measuring these things really really precisely. And so it set the stage for the Higgs discovery.

00:35:08
Speaker 2: Okay, and then what about the LHC.

00:35:11
Speaker 1: Yeah, so the Large Hadron Collider, which we're still running. This is protons and protons, so not protons and anti protons. They made a different choice here, and one reason they did is that they wanted to go for really high rate. It's easier to make high rate collisions of protons and protons because protons are everywhere. Anti protons hard because you got to make them. It's like manufacture antimattery, which requires like starting from a beam of matter and smashing it into this stuff and filtering out the rare anti protons and then storing them. It's really complicated to make antimatter and smash it together. So they were like, let's just do the easy thing proton proton, because protons are everywhere and they're simple and they're stable, and then we can do it really really high intensity for a long long time in order to look for really really rare things, and they discovered the Higgs boson. Who you might be wondering, like, how does a proton interact with another proton? Don't you need matter antimatter? Well, remember the whole protons not interacting with the other proton. You have like a bag of quarks, and you have gluons, and so actually what happens most of the time at the Large Hadron Collider is gluon gluon collisions, So it's really kind of a gluon collider, which is crazy.

00:36:18
Speaker 2: That is crazy. And then there was a particle collider that was partly built in Texas before we gave up on funding it, right, What kind of particle collider was that going to be?

00:36:28
Speaker 1: Yes, so the superconnecting SuperCollider, which never happened, unfortunately, That was going to be very similar to the Large Hadron collider. It's going to be proton proton in the same way, and so it almost certainly would have discovered the Higgs boson. Also, it was going to be like three times more energy than the Large Hadron collider. So it would have revolutionized particle physics. Like they would have built it and discovered stuff which today is still out of our reach. Like thirty years ago, they would have known the answers to questions. We still don't know the answers to such a shame.

00:36:57
Speaker 2: Does the tunnel still exist?

00:36:59
Speaker 1: The tunnel still exists and is mostly filled with water.

00:37:02
Speaker 2: Ah, well, let's start that project again, all right? Well, Daniel, Well, you and I go look for funding to start that project again. We'll take a break and when we come back, we'll talk about why we should be smashing muons into each other. All right, Daniel and I still have not figured out a way to get funding to resurrect that particle collider in Texas. I thought Texans like to go big, but apparently they don't like to go that big. And now we're talking about muons.

00:37:46
Speaker 1: So muons are attractive to use for a collider because they might be the best of both worlds. Remember, muons are like more massive electrons. And the only negative thing we had to say about electrons was they were so low mass that when the ways around corners, they lost a lot of their energy. So it's hard to get electrons up to high energy. All right, we'll just swap in muons for electrons. Now they have more masks, they can get to higher energies. Right, So now they are like very high energy, and they're cleaner than protons. Protons are these messy bags of quarks with the strong interaction. So this is like taking something which is massive like the proton, but clean like the electron.

00:38:24
Speaker 2: And would we need muons and anti muons or could we just smash muons into each other.

00:38:29
Speaker 1: You could just smash muons into each other, but you'd learn more if you smash muons and anti muons into each other. Absolutely, and to make the same kind of discoveries, and a muon collider you don't even need to get the muons up to the same energies as the protons. Remember, protons are bags of three quarks, so you accelerate the protons to like ten trillion electron volts. Each quark only has like three trillion electron volts, and that's what goes into your collision to make those same discoveries, and a muon collider you only need to bring your muons up to like three three zero point three trillion electron volts, not all the way to ten. So it's easier to make these discoveries at a muleon collider because it's fundamental, because or at least we can't tell if it's not fundamental, and so there are real advantages there. The kind of physics you can do at a muon collider is very powerful at lower energies and yet clean like an electron collider.

00:39:20
Speaker 2: And so what do we think we would discover that would be different if we used a muon collider than if we had, you know, the pre existing electron colliders.

00:39:29
Speaker 1: Yeah, so muone colliders can get to higher energies, Like we think if you built a mule collider at just ten trillion electron volts, it could discover the same kind of things that a proton collider at one hundred trillion electron volts could discover. So it's like ten times more efficient in that sense per discovery because at one hundred ero electron volts, protons are insane bags of gluons and most of the energy is just in the gluons, and every collision is very inefficient. You're not really getting any fraction of that one hundred trillion electron volts, whereas mule ten trillion electron vaults. You can really precisely tune those interactions and you can find all sorts of crazy stuff. Plus there's the added bonus. Remember we said that muons have more mass, why because they interact with the higgs more. That means that if you collide muons together, you're going to get more higgses because muons interact with the higges. And when the universe is like making its draw from its random probability distribution, what are we making today? If you start from muons, then the higgs is are a bigger part of that probability distribution than if you start from electrons, because electrons hardly interact with the higgs boson because they have such low mass. So, in that sense, a Muon collider is like a Higgs factory. It'll make tons and tons of Higgs bosons for us to study and learn about.

00:40:43
Speaker 2: So the LC is where we discovered Higgs. What would we learn if we saw more higgs?

00:40:52
Speaker 1: Great question. So we found the Higgs, but we don't really know is this the Higgs that Peter Higgs predicted or is it like a weird version of the Higgs? And so the next thing is to study it in detail, measure its mass, measure its properties. Remember how we measured the top and the W and the z at a large electron positron collider, and that set the stage for the discovery of the Higgs, because all those particles properties really only made sense if the Higgs was there. So what we want to do is study the Higgs and gory detail and see like, well, is it decaying as a dark matter? Is it interacting with something else? Are there two Higgs bosons? These kind of things can be revealed if we studied the Higgs in great detail. So far we haven't seen any hints of that, but you never know what's around the corner.

00:41:35
Speaker 2: Are there theoretical predictions that I guess you've you're already not sure you've seen the only version of the higgs. So there's probably a lot of questions you all have.

00:41:44
Speaker 1: There are, and there's lots of predictions about models with two Higgs bosons or three higgs bosons, all sorts of crazy stuff that we're excited to look for, and a muon collider would be a great way to do that and be very powerful in its physics reach.

00:41:58
Speaker 2: Cool. Okay, so we've tried to figure out if electrons are fundamental by smashing them together and nothing has come apart. Is there any reason to think that muons, being essentially heavy electrons, would be more likely to break apart if there was something break apart a bowl about electrons and muons.

00:42:18
Speaker 1: No, not necessarily, so if they are fundamental, then there's no reason to imagine muons would be easier to break apart than electrons. But the advantage is it's easier to get muons up to higher energies. If there is some threshold above which you can see inside electrons and muons, it's much easier to get muons over that threshold than electrons. So in that sense, we're more likely to discover that muons are made of something else little bits and bobs than we are of electrons.

00:42:44
Speaker 2: All right, well this sounds like a slam dunk. Why wouldn't we do this?

00:42:50
Speaker 1: Well, one of the real challenges is that muons are not stable. Like you have a pile of electrons, they're going to stay a pile of electrons. The protons that are inside you have been protons since the Big Bang, Like these are really stable things. Muons last for two point two microseconds, So you can't just like say, hey, I've got a big pile of muons in a drawer, do you need any Right, you open that drawer, They're gone two point two microseconds. That's you know, ten to the minus six seconds, So it's not a lot of time, which means that number one, there aren't muons around. You can't just go like go dig up muons like you want electrons and protons. You just start with hydrogen, which is everywhere, and you separate and you have protons and electrons easy. If you want muons, you have to make them in collisions of other stuff and filter them out and then they disappear after a millionth of a second. So there's a lot of challenges here. So making them accelerating and cooling them and colliding them all within microseconds is not an easy thing to do.

00:43:52
Speaker 2: And what about anti muons, which you'd probably want for these collisions. Is that harder still?

00:43:56
Speaker 1: Actually, it turns out those are just as hard, so there's a bonus. Yeah, So where do you get muons?

00:44:02
Speaker 3: Like?

00:44:02
Speaker 1: There actually are natural sources of muons, because protons are hitting the upper atmosphere all the time, and when protons hit the atmosphere they create showers of particles, some of which decay into muons. So you know, muons are passing through you all the time, but not at the rate we need for the large Hadron collider. And so what they plan to do there is they're going to make their own muons. They start with protons, which are easy to get, They accelerate those up to reasonable energies, not crazy LEDC level energies, and just like smash them into some block of stuff like you know, carbon or whatever, and out the back comes a bunch of different particles kons, pions, whatever, and a lot of these will decay into muons. And so then you use a magnet to filter out the ones that you want, because a magnet will bend to charge particles, so you get like muons going one way, anti muons going the other way, and other stuff goes at at a different angle because it has a different mass. So now you have your muons and the clock starts ticking. You have a millions of a second to accel wait these things and smash them together. But fortunately physics comes to the rescue because if you get them going at really high speed, you can take advantage of special relativity. Remember that moving clocks run slow, so if you have a muon sitting on your table, it lasts for two point two millions of a second, but a muon going at almost the speed of light can last four minutes and minutes because its clock is running slowly. That's the only reason why muons make it all the way down from the atmosphere to the surface of the Earth. They're creating the upper atmosphere, and two microseconds is not enough time for them to get here, but their clocks are slowed down because they're relativistic, and so there's enough time for them to get here. In the same way, we get our muons up to high speed, then we actually have longer to play with them.

00:45:44
Speaker 2: Okay, that's awesome, right, So we've got a chance of making this work. Did I hear you say at the LHC. Are they starting to do this at the LHC. Or did I mishear you.

00:45:52
Speaker 1: I'm not sure when I said, we're not doing this yet. This is like very experimental technology. There's a lot of stuff that has to happen here. You have to make the muons, and then you need to do something called muon cooling, because the muons that are made come out of a spread of energies and directions, and you need a bunch of muons all organized, like you want a marching band of muons where everything is the same energy in the same direction. You don't want like a mosh pit of muons. And so they do something called muon cooling, which is basically getting them all in line. It means like reducing the phase space that these muons are in in sort of velocity and location. And to do this they like pass them through a bunch of filters which tend to reduce the energy of the muons more for the higher energy ones, and so bring them sort of together coalesce them. This is something still experimental. We're not like experts in muon cooling, but the way we're experts in dealing with protons, for example, because nobody's done this before. So it's sort of like a technology that's being developed. And then you have to accelerate these particles really fast. Protons, you've got lots of time. It's like pushing your kid on the swing. You can push very gently all afternoon until they get up there. But with muons, a clock is ticking, so you have to accelerate them like really quickly. It requires different kinds of technologies. So what they actually want to do is separate the rings into an accelerating ring and acceparate colliding ring. So you have an accelerating ring where you do like these crazy rapidly changing magnetic fields to accelerate your muons really really rapidly, and then you move them into a ring where you can collide them together and observe those collisions to see what comes out.

00:47:22
Speaker 2: So when you say that they last two point two microseconds, but they last longer because of time dilation. When they disappear, what do they become? So, like you said, they're not stable, do they decay into electrons that then mess up your experiments and they need to be pulled out, like what happens to them?

00:47:41
Speaker 1: Yeah, that's exactly right. They decay into electrons and then two neutrinos, and the neutrino's mostly invisible. But that's actually a problem because now you have like sprays of high energy electrons filling your detectors, which is bad, and so you have to work on shielding to block all those electrons from your detectors. You want to just see what happens when muans colliding. You don't want to be buried under like massive sprays of electrons from all of your decaying muons, And so it's complicated. There's a lot of technology here that has not been fully developed. We think we know how to tackle these problems, but some of this is sort of in the like, we have an idea, we think it's going to work, let's try it. There's always surprises around the corner. So the timeline here is like, maybe we're going to get the funding together. If we can convince everybody to build a demonstrator, like a mini version in the twenty thirties, and if that works, then we can ramp it up and start building a massive one, which we hope would turn on in like twenty fifty.

00:48:36
Speaker 2: Wow. Yeah, And so is there like a consortium of scientists then writing up this grant.

00:48:42
Speaker 1: There is a community of folks, the Muon collider community. They're very engaged, they're very active, they're very energetic. I think they have a good case. But there are other people who think, no, let's build another proton proton machine, or other people who think no, we should build a linear accelerator with electrons and positrons have to worry about any magnets. So the field right now is a little bit split into different camps about what the best thing to do is. It's all very congenial, people disagreeing in good faith, but there's not a whole lot of clear consensus about what the next step is. And it's sort of an unusual moment in particle physics. Usually we have one collider running and another one we're building, which is why we had this sort of zigzag we talked about before, like the Tevatron and then LEP and then the Large Hadron collider. But right now we're operating one and we're not building another collider. China has said maybe they'll build one, but they don't really know. Cern has said they could build one hundred TV machine, but we don't know if the money is there. Other people are pushing for this Muon collider, and so we don't really know what the future holds for particle.

00:49:43
Speaker 2: Physics and what is the cost of a project like this, Like if Musk decided he really wanted a particle to be named the musk On, and he decided he was going to build one of each of these particle colliders, like, could he afford to do that? Or are we even exceeding Musk's vast wealth.

00:50:00
Speaker 1: No Musk could afford to do that. I mean, I don't know what his liquid assets are, but you know these are things that cost tens of billions, maybe up to one hundred billion dollars. So definitely Musk, who is likely to be that the first trillionaire, could afford to build one of these things and insist that it'd be named after him. In fact, you know, since his name starts with mu you can imagine some clever play on words there.

00:50:22
Speaker 2: Yeah, absolutely, and that would have been a much.

00:50:24
Speaker 1: Better Muskon collise.

00:50:25
Speaker 2: There you go, that's right, that's right. That would have been a much better purchase than x, I think. But anyway, this is why I am not in the tech industry, nor am I an entrepreneur. I don't know what good investments.

00:50:36
Speaker 1: Are, nor are you a business advisor to billionaires?

00:50:38
Speaker 2: That is exactly true. Yeah, I have made lots of suggestions for how he could spend his money in my book and on shows, and he doesn't seem to be listening. But that's okay, all right, Well, this was fascinating. I hope that physicists find ways to have more of all of the different fun colliders that they want to be working with.

00:50:56
Speaker 1: Yeah, me too. These are really fun toys. The most exciting thing are the potential surprises. These colliders really are ways to explore the universe without going anywhere. If you're excited about like landing a probe on a new planet, because you never know what you're gonna find, that is exciting. And it's the same kind of excitement when you turn on a new collider at a new energy. Nobody has colliding particles of this energy before, You have no idea what on nature's menu will be revealed, and that is really exciting. So I hope we get to build these things because the only obstacle between us and understanding is money. We are in the candy store of universal knowledge, and we have the money in our pocket, and we're just deciding, Hey, should we buy those suites or not?

00:51:38
Speaker 2: Or should we cure cancer and give it to the biologists? Ah, who's a better investment you decide?

00:51:45
Speaker 1: No, No, it's a false choice. They're all good investments. All of these investments pay for themselves, and so it's not a zero sum game. We should do all of it. Let's cure cancer and build a mere on collider.

00:51:55
Speaker 2: Amen, you're right. Why am I dividing us, Daniel when we could be brought together instead?

00:52:00
Speaker 1: All right, believe in the universe, invest in humanity. Let's go explore it.

00:52:04
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