Episode 6: A Final Moment for the Muon

Who speaks in this episode?

• Steven Goldfarb (Host)
• Fred Gray (Host)
• Claudia Cornella (Host)
• Zimma Kubeski (Host)

What is discussed, and when

1. 0:00 – 5:00: CERN, muon g-2, Steven Goldfarb, Fermilab
2. 5:00 – 10:00: Fred Gray, LHC, South Korea
3. 10:00 – 15:00: LIGO
4. 15:00 – 20:00: QCD
5. 30:00 – 35:00: Steven Goldfarb, Fred Gray, Regis University
6. 35:00 – 35:11: Steven Goldfarb

Notable quotes from "Episode 6: A Final Moment for the Muon"

• Hello everybody and welcome to Early Morning Coffee at CERN. My name is Steven Goldfire.

  about Steven Goldfarb · at 0:09

• Science and technology which is in a spirit of our previous podcast. of course everything we do here at CERN basically or at Firmmy Lab has to do with quantum mechanics…

  about CERN · at 2:27

• As many of our even larger collaborations that are here at CERN and it didn't even start at Firmeny Lab did it I mentioned Brook Haven And it started there, right? I would even say before that it started with a series of three.

  about Brookhaven · at 9:10

• Important to note here because I love to wax poetic about the experiment I work on. I work on the Atlas experiment and it's an enormous thing. It's it's some half of a football…

  about LHC · at 11:59

• That's that's a good definition of precision. I think the only experiment that beats us I can tell you there is one that beats us. That would be LIGO, right? Their measurements of gravitational waves. Impossible. I don't.

  about LIGO · at 12:58

• It's called Latis QCD and it's really the only method that we know that reliably can tackle these this strong interaction these hydronic properties of a theory.

  about QCD · at 19:26

• Accelerators than that even that we still use as well. Well thank you very much. Fred Gray is professor of physics at Regis University in beautiful Colorado I think it is. and…

  about Fred Gray · at 32:53

Who and what is mentioned in this episode?

People

• Steven Goldfarb — Person · Host / main interviewer · 3 mentions · first at 0:15
  Leads the episode, frames the muon g−2 topic for a general audience, and moderates discussion between theorists and the experimentalist.
• Fred Gray — Person · Co-host (and featured experimentalist guest voice) · 3 mentions · first at 0:23
  Introduces and explains the experimental side of the muon g−2 measurement, including why muons are ideal, how the experiment achieved precision, and what comes next (J-PARC, MUonE).
• Claudia Cornella — Person · Co-host / theorist contributor · 1 mention · first at 0:20
  Explains theory concepts (spin, magnetic moment prerequisites, why precision theory is hard) and discusses how discrepancies can imply new physics (ALPs, Z′ models).
• Zimma Kubeski — Person · Co-host · 1 mention · first at 0:21
  Introduced as one of the show’s hosts; participates lightly in the opening host roll-call in the provided excerpt.

Companies & orgs

• CERN — Company · Headquarters · 2 mentions · first at 0:15
  Primary location where the podcast is hosted and where much of the discussed research takes place.
• Fermilab — Company · Research Facility · 1 mention · first at 0:38
  Key location for the muon g-2 experiment discussed in the podcast.
  Was on the these results and it might not sound familiar to you as a physics topic. It's from the muon g minus2 experiment at firmy lab. But the topic is really nice. And I…
• Brookhaven — Company · Research Facility · 4 mentions
  Previous location for the muon g-2 experiment before it was moved to Fermilab.
• LHC — Company · Research Facility · 1 mention · first at 7:47
  Mentioned as a comparison point for the precision of measurements in particle physics.
• LIGO — Company · Research Facility · 1 mention · first at 13:06
  Mentioned as having even more precise measurements than the muon g-2 experiment.
• Regis University — Company · Affiliation · 1 mention · first at 32:57
  Affiliation of Fred Gray, one of the guests on the podcast.
  Accelerators than that even that we still use as well. Well thank you very much. Fred Gray is professor of physics at Regis University in beautiful Colorado I think it is. and…

Concepts & topics

• QCD — Concept · Key argument · 1 mention · first at 19:39
  Quantum Chromodynamics is discussed as a fundamental theory in understanding the muon's magnetic moment.

Places & events

• muon g-2 — Event · Core topic · 1 mention · first at 0:38
  Main subject of the podcast, discussing the precision measurement of the muon's magnetic moment.
  Was on the these results and it might not sound familiar to you as a physics topic. It's from the muon g minus2 experiment at firmy lab. But the topic is really nice. And I…
• South Korea — Place · Collaborator Location · 1 mention · first at 9:06
  One of the countries contributing to the muon g-2 experiment.
  Contributions from places including Italy Germany the United Kingdom South Korea and China wow okay so it's it's as international as many of our even larger collaborations that are here at CERN and it didn't even start at Firmeny Lab.

Full transcript with timestamps

0:00 Nobody wants to do this. Come on, somebody be great. Tell me. I got two theories here and an experimentalist.

0:06 No one knows why. I mean, we know. Hello everybody and welcome to Early Morning Coffee at CERN. My name is Steven Goldfire.

0:20 I'm Claudia Cornella. My name is Zimma Kubeski. And I'm Fred Gray. And we have an amazing show for you today. It's something that is a result that really impressed me. We just had a presentation made last week I think it was on the these results and it might not sound familiar to you as a physics topic. It's from the muon g minus2 experiment at firmy lab. But the topic is really really nice. And I think the thing that caught my eye was the degree of precision, the amount of work that went into getting this measurement, a measurement of the magnetic moment of the muon, which is weird. So I want to start out with that. I want to try to understand first of all to explain what is a magnetic moment.

1:07 Well, when I think of magnetic moments, I actually go back and think about bar magnets, the kind that everybody played with as a kid. And you know that some of them are stronger than others. And so the strength of a bar magnet reflects its magnetic moment. And you know, why is that magnet magnetized? It's magnetized because it's built up of a lot of subatomic particles. and the spins of the electrons inside um all add up to the magnetic moment of the whole bar magnet.

1:40 Okay, there there's a lot in that. Okay, first of all, so so but a muon a muon is just a simple particle, right? It's an elementary particle. It's like an electron but more massive, heavier, right? There's electrons, muons, towels. Those are the three lepttons. I don't know Claudia maybe you can explain to us what why would a muon have a magnetic moment

2:04 because muons have spin uhhuh and if you want to some extent to spin is like a rotation but it's not a rotation in a physical space

2:15 it's really a quantum property of the particle okay okay I don't know if that helps

2:21 well I think it does a bit but let me let me first of all we should acknowledge that this is the international year of quantum science science and technology uh which is in a spirit of of our previous podcast. Um of course everything we do here at CERN basically or at Firmmy Lab uh has to do with quantum mechanics, quantum field theory. Um but that's a strange thing though. You have to admit that's a strange thing. So an elementary particle is something which has no structure to it. You you can't really think of it as spinning in in space, but it has some property that that's spin. I mean, why?

2:58 Why? And how do we figure that out? Nobody wants to do this. Come on, somebody be brave. Tell me. I got two theorists here and an experimentalist.

3:10 No one knows why. I mean, we know that it's the case, but no one knows why they have spin. I mean we just

3:17 found out by the way they interact that there has to be this property that is like a tiny magnetic I mean like a rotation but there can't be

3:26 right and this is what we have to live with I mean sometimes it's really just difficult and hard to understand but it is what the theory tells us

3:33 but it it is a really important property in the end right because this is what defines the the the properties of of of material versus say the force carriers right force carriers have a spin integral spin or in the case of the Higs Bzon zero spin which is still integral that's carrying the force and then electrons and muons and towels and their nutrinos have spin 1/2 so there's a certain that's that that's the amount of spin they have but I guess we learned about this because you can add that spin onto angular momentum somehow right you can add that on to to that value but okay so this is somehow somehow magically this this elementary particle has this property and that gives it a magnetic moment. And how would you with theory tell me what what that magnetic moment should be? What would you guess it would be?

4:29 Well, one thing to say is that spin is not enough in general to have a magnetic moment

4:35 in the case of an elementary particle. You also need a particle which is charged.

4:40 Okay. Okay. Um instead if you have a composite particle so a particle which is made um out of smaller building blocks that can have a magnetic moment also if it's electrically neutral for example the neutron

4:54 Mhm. is made of up and down quarks which are individually charged. Okay. And you can imagine them to move a bit in the in the nucleus.

5:02 Okay. So the charge distribution of the neutron even though the neutron is overall neutral

5:08 has a non-trivial shape and this in combination with the spin is what allows you to have a magnetic moment. So not every particle has a magnetic moment.

5:18 Not every particles but the leptons apparently do because they do. Yeah. They all do. So we have electrons and muons and tows and uh why maybe I can ask Fred why did you guys at Firmeny Lab and first at Brook Haven decide you wanted to measure uh the magnetic moment of the muon.

5:38 The muon is really kind of ideal because it has the the perfect combination of mass and lifetime. So it's uh it turns out that if you're looking for the contributions of new physics to the magnetic moment of a particle um it helps if that particle is more massive and the muon is about 200 times more massive than the electron um and that amplifies its sensitivity to new physics by a factor of about 200 times squared. And so that means um yeah that it's a great laboratory for searching for new physics but also um yeah we have to have them around long enough to be able to study. So uh the lifetime has to be long enough. Of course electrons live forever, right? They're stable particles and the magnetic moment of the electron has been measured in the lab incredibly precisely. Um but it's not really so sensitive to new physics. Meanwhile, the lifetime of the towel is incredibly short. It's not long enough to be able

6:47 to study it effectively. And so, the lifetime of the muon is long enough that we can circulate them around um you know, at rest a muon lives on average a little more than two micros. in our experiment about 64 microsconds um because they're moving at close to the speed of light which actually increases their lifetime from our point of view because um their clocks are running slowly. This is a really interesting thing from special relativity.

7:16 So there's a secret to longevity if everybody if you really want to live long move really super fast. And uh I mean this is why we know about muons, right? Muons hit us over the head all the time. uh not to scare you but while we've been talking hundreds of muons have gone through you through your head from uh interactions in our in our upper atmosphere

7:37 and that was one of the things that got us started out on the whole path of doing particle physics right we saw mother nature's doing this all the time I saw a calculation once that said that mother nature had done the whole LHC program about 10,000 times already in our upper atmosphere so another reason to see uh that it's a safe thing this has happened we've done this, but we just didn't have our detectors around to measure everything that was happening at the time. Um, but okay, so let's get back to to the M. Well, actually, we should mention this that there's that lifetime, but uh the TOAO is much more massive. So, that's the difference between these guys, electrons, muons, and TOAS. And it turns out that when you're more massive, uh, as my wife tells me, uh, you're going to decay more quickly. Uh, but it's true for elementary particles. uh the more the heavier they are, they have more ways

8:29 they can decay in. Right. Decay is a terrible word. I hate to use decay because they don't really

8:34 change. Yeah, they change. Transform. They transform from one type to another. They don't actually It's not like there's a muon. There's no electrons inside a muon, right? It's still an elementary particle. Okay. So, you've made this really nice measurement. Not just you. your whole collaboration

8:50 176 of us 176 of you working on this from all from the US because it's in firmy lab

8:55 no it's very much an international collaboration um with a lot of uh major contributions from places including Italy Germany the United Kingdom uh South Korea and China

9:08 wow okay so it's it's as international as many of our even larger collaborations that are here at CERN um and it didn't even start at Firmeny Lab did it it I I mentioned Brook Haven And it started there,

9:19 right? I would even say before that it started with a series of three experiments here at CERN. And then after that came an experiment at Brook Haven that I worked on for my PhD. So I've been doing this for quite a long time now. We were taking that data back in the late 1990s, early 2000s. And we had an opportunity to relocate the experiment to Firmeny Lab long after we were done at Brook Haven. Um because at Firmeny Lab they really had some great ideas about how to with their accelerator complex serve up an enormous number of muons to the experiment um in small little batches for us which turns out to matter

9:59 um and so with many many muons because really our experiment is still limited by the number of muons that we've counted by the statistics

10:09 and um with them divided up so that they don't pile up with each other as they decay so that uh we can count each muon decay separately.

10:20 Wow. So that's uh you know the motivation for moving it there to Fermy lab. So and that was easy right? You just put it in a box and ship it uh you know UPS or or

10:31 Well um when we first got started talking about the logistics we were actually talking about picking it up with a helicopter and moving it with a helicopter to a barge in the port. It turns out the helicopter idea was not so practical. So it went onto a truck to a barge around uh the tip of Florida into the Gulf and then up through the rivers and um up to the port of Limont near Chicago and um then back onto a truck on the uh uh the tollways in the Chicago area out to Fermy Lab. So I bet quite a production.

11:08 I bet everybody loved the traffic jam. Uh I got to ride along with it one night and yeah, you could certainly sense that at the closed onramps to the tollway. Um people were a little bit annoyed, but at the same time, I think it was worth it for the science that we got.

11:25 Sure. Sure. Well, I mean, we we've been through that here. Uh I remember taking my my my son to to to school actually at CERN has a little school for when they're very young and and us being slowed down because there was a blue dipole. My son at three was already saying, "Look, dad, a blue dipole." So, we we've had that. So, when you when you do these major things and when we build our future accelerators in the local areas, we'll have to make sure they understand it's a slight sacrifice, but it's worth it for the for the science that's being done.

11:53 So, I I mentioned um um the amazing precision and uh I think that's important to note here because I love to wax poetic about the experiment I work on. I work on the Atlas experiment and it's an enormous thing. It's it's some half of a of a football pitch in in length. And uh and so over these these sort of you know 46 meters we we also line up our detector at the far ends to you know tens of of of microns. Right. So that means we have one in a million precision. Now your measurement gives us a precision of what what amount?

12:29 A little better than 140 parts in a billion. And so that is uh you know the analogy that I've heard recently from one of my colleagues is that they have these big animals a little bit bigger than cows at Fermy Lab. Bison um they're famous and um so the precision is about one sunflower seed out of a whole bison.

12:52 Okay. So if a bison were to eat one more sunflower seed, you could tell the difference with in that level of precision.

12:57 That's right. That that's that's a good definition of precision. I think the only the only experiment that beats us I can tell you there is one that beats us. That would be LIGO, right? Their measurements of of gravitational waves. Impossible. I don't know how they do it. That's impossible. But you did a lot of work to get that far. But what I'd like to know actually I turn to theory now. Okay. Uh because Simon's also working on trying to improve theory. This is a very interesting thing because you guys have them beat a little bit here. The precision of the measurement. Tell us about that Simon. What what's going on?

13:27 Why is theory not able to to have a smaller error bar than the experiment? I mean the reason is not that we were not trying. So actually I mean before these guys built their experiments there was this G minus 2 theory initiative. So really hundred of people from all over the world coming together with the idea that we should give our best to have the I mean really the most precise prediction of the theory. to really do the best doing calculations um to be able to compare to experiment and it was clear that um we have to improve and that the experiment would be very precise um but it's an incredibly difficult calculation to do

14:07 so I mean the question is what is happening there and the point is that at this precision we're talking about everything matters really everything in the sense that this muon and magnetic field

14:21 doesn't only talk to the magnetic fields which is composed out of photons but they're all these quantum fluctuations and it's really talking to all the forces in the standard model which are the weak interaction the strong interaction and the electromagnetic interaction.

14:35 Okay, that's a strange thing. Let's just try to wrap our heads around this for a second here. So everything's going on, right? You have a certain amount of energy. I know that if we take our protons and accelerate them, it turns out there's things popping in and out of the vacuum out of nowhere. Uh, and perhaps the big bang was us just popping out of nowhere. I don't I don't know. But but that's happening right at high energies. So, I don't know. Maybe Claudia, can you explain to me a little bit of ho how does this work? How how is it that um we don't get an answer that's precise that's we we we have to sort of expand, I guess. H how does that work?

15:17 Okay. It's complicated to explain. It's complicated. I'm gonna I'm gonna try. Okay.

15:22 Um well, in general, when we when we try to make a prediction for an observable to make a a calculation that then can be compared to to the experiment, ideally we want to try uh to do it in the simplest way possible.

15:37 Mhm. And depending on the precision of the experiment, we need to get a certain precision on our theory prediction too. We kind of want to match that precision. Mhm.

15:49 If the experiment is not very precise, it might be enough to make some we can call it some sort of approximation which is good enough to get uh a prediction of the same yeah precision as the as the experiment. But as experiment get more and more precise

16:05 um we cannot do these approximations anymore. Mhm. And then things become very easily much more complicated. Now in general um depending on the type of interactions you're looking at um it might be possible that at every if you want difficulty step the effect gets smaller and smaller. So by doing the first we call order computation you already get the bulk of the result.

16:33 But what these guys in practice deal with is a situation where everything matters at the same time. There is no approximation. everything everywhere all at once. I guess what's going on here? So I mean it it is a very interesting because most people would think all right and and it's very normal to think this uh that you have a theory and the theory will tell you well it should be two you know that this is this is it you know you have a simple thing you have a muon here it is it's got a charge and a spin and you do your calculation but it turns out because of the energy uh that things can pop in and out of a vacuum uh you end up having to do and this is this This is what actually drew me into the field I have to admit in quantum field theory was that when you have an interaction there are a lot of different possible things going on right so I always mention this uh when I talk to people about what goes on with

17:30 collide protons uh and and these two quark let's say or two gluons interact there's many different ways that that can happen and we're not even allowed to see that right we never know so you guys never really get to get inside there and see what's what exactly happened with this muon becoming an electron. And it could have gone it through many different paths. Some of those very complex, but the more complex they are, the smaller the probability. And some of them straightforward. And you end up with this sort of infinite sums, right?

18:00 You get something that we we learn if you go far enough in math at school, you'll find these sort of expansions. and and there you see that that that the the bigger the the the further you go the smaller the numbers are but as you're saying uh in this world in the world of the the muon here you have to go out pretty far to get the precision and and Simon's just not getting it done what

18:27 no it's really complicated I mean so there's the frustrating thing maybe is that 99.99% of this theory prediction is is based on this electromagnetic interaction and people can compute it very nicely and it's super precise and then there's this small piece it's called the hydronic vacuum polarization contribution and that's basically I mean there's the muon and then there's a photon that tells the muon how strong the magnetic field is

18:54 and then this photon makes a quark anti-quark pair and as soon as we have this everything happens it's there are tons of particle and everything happens at the same time and we cannot just sit down and write a formula and and get to result and we cannot even go to a computer and press a button and get the result.

19:13 Uhhuh. So we have to go to a computer but it takes years and years and the biggest computers in the world to get to results that we have

19:22 to understand this this sort of there's a name for this right lettuce QCD. It's called Latis QCD and it's really the only method that we know that reliably can tackle these this strong interaction these hydronic properties of a theory.

19:34 Yeah. So just to recap I mean the strong interaction but there's for some reason there are people out there who don't know about QCD and the strong interaction they ought to uh and that's you know the interaction between quirs quirs are what put we put them together we make protons we make neutrons out of them and there's a whole lot of other hadrons our friends at LHCb are finding new combinations all the time penta quarks and all these different things or excited states of these but in this case you can produce these these pairs and when you do that lots of different things can can happen. So, uh so I guess I mean I should note that that we had to bring on two theorists because the experimentalist has done his job over there. Um but uh

20:16 and the theory is really more than twice as hard, I have to say. Yeah. Okay. It it is it's it's a very hard job to try to get this down. And one thing that's important to note is at no point are either of you guys trying to be like the other, right? So you're not saying, "Oh, my result is is over here." And for a while it's been like that, right? The result of the measurement has been a little bit aways from theory which makes it intriguing and interesting. But all you're trying to match up is the precision. Try to get as good a precision or better than the other and then you'll see what nature tells you if if they agree. So maybe uh Fred you can expand a little bit more on how because you guys did an amazing job to get the precision that you have. What did you have to do?

21:00 Right. Well, the first key was simply measuring an awful lot of muons. So, um we recorded a little more than 300 billion um final uh events that made it into our final data set. And to do that, we actually had to store more than a trillion muons in the storage ring. So, that uh was really the first key was simply having this incredibly um high statistical power. And then we really had to pay attention to like you said before um everything everywhere all the time. So we had to focus on um really improving every possible systematic error. And you can see going from one year to another the kinds of things that we improved. So for example um our experiment the the technique really relies on what's called the magic momentum which is to say that the muons have exactly the right momentum that the electric fields don't rotate their spin so that we can use large electric fields to confine and focus them inside the

22:08 storage ring. And yeah on the other hand not every muon is going to have exactly the same momentum. Some will be going a little fast and some will be going a little bit slow. So for this most recent result, we just had to work much harder on measuring the distribution of momentum including building a whole new detector like um some of my colleagues at the University of Washington did. They call it the mini sci-fi. And so we introduced this in order to get just that much uh better precision on what we knew about the momentum. And you know for example um we need to know the magnetic field incredibly precisely that the uh that the muons experience

22:48 and so there in um yeah we've been measuring the magnetic field in a sort of static way. So uh the the part of the magnetic field that doesn't vary with time by pulling a trolley full of magnetic field probes all around the inside of the vacuum chambers at a time when the muons aren't there. But for this most recent measurement, we also were able to measure the time dependent magnetic fields from when we fire the kickers that kick the muons onto the correct orbit

23:22 and from when we energize the um quadripole plates that make the big electric fields that confine the particles. So, uh, you know, very precise measurements of those things were included progressively as we moved from the analysis of one run into another to get to better and better precision.

23:42 And we're at the point now where really we would again have to improve everything if we wanted to continue to make progress here. We've really gotten those systematic errors down um, as small as we practically can.

23:55 Yeah. Okay. I that that's so there's a few technical terms I should mention here you kickers for example or quadruples but these are all sort of means of using electromagnetic fields uh you have an electric field to push things along make them go higher energies and then and then your quadripoles also will do they focus or they uh

24:16 they are for focusing that's right and actually we don't have anything that um that changes the energy of the particle once it gets into the storage ring um the kicker just redirects the particles from um an orbit that would come around and hit the injection point again onto an orbit that would be stored in the vacuum chambers that uh you know sort of centers it right in the middle of the the quadripulse.

24:40 Okay. Okay. For those watching actually on YouTube, you have a picture of it. It's a it's a relatively small accelerator compared to what you see here at CERN. Usually

24:49 14 meters in diameter. 14 meters in diameter. Uh but it's an amazing thing and actually it has an interesting part to it. I noticed that when when the muons come in there's there's like a gap,

24:59 right? There's like a space between the the magnets. Uh and that it's fine. Muons just keep going. Right.

25:06 Right. Um over a short distance that's certainly true. Although over a long enough distance you certainly want to have them in a vacuum so that they don't scatter off of the uh the air.

25:17 Beautiful. It was a beautiful, beautiful experiment and congratulations on getting such amazing results. Um, I do want to ask go back to the the the the slight discrepancy that there was and maybe it's disappearing. We don't know. Um, what can we learn when we do a precision measurement like this? U maybe I ask Claudia if you do a precision measurement, how does it help us uh when we compare it to to to theory? What can we gain from that? Well, whenever there is a discrepancy in a precision measurement, um especially if if this discrepancy is statistically significant like it was in the case of the G minus 2, um we as theorists, all we want to do is to try to find out which type of new particles and forces could explain that discrepancy.

26:07 So, precision measurements are the perfect venue to do this. Uh-huh. Um, in some sense by looking at a discrepancy, we can learn several things. We can learn something about possibly the scale, the mass of the particle

26:25 that explains the discrepancy. Mhm. And also something about its coupling. Okay. Coupling being how they interact.

26:32 How they interact. Yes. Um so for the case of the G minus 2 um two of the most common explanations were one in terms of very very light particles called axion-like particles.

26:46 These are particles that arise um for example in models trying to explain dark matter or to solve another big problem of the standard model which is called the strong CP problem. Mhm.

26:58 Or also other types of particles like for example uh heavy boss like heavy Zet Bzones that couple differently maybe between electrons and muons and towels etc.

27:11 Mhm. Then in practice when when we build one of those models we also have to to to pay attention because in general the moment you have a new particle with new interactions it's not just going to pop up in one measurement but it's also going to arise somewhere else

27:27 and then you have to make sure that your model doesn't contradict other data. So somehow from these small discrepancies um if they are confirmed if they are statistically relevant

27:41 um we can definitely learn something about what is beyond the theory that we know right now. So and we know that there is something beyond it because there are several problems it doesn't address.

27:51 Exactly. Exactly. And that's that's it's important to note that we have this amazing theory and we keep testing it and uh and we'll be doing many more precision tests here. For example, at CERN, we're always doing precision tests as well. We're not just looking out there. Is there a new particle out there? We do that and we love that. But we also we will be in fact any year tearing apart the LHC and our experiments. At least Atlas and CMS are going to be refurbished to go to high luminosity and in which case when we get much more many more collisions like you need lots of muons, we need lots of proton collisions and with that we get the higher statics, we get higher precision and we can look for very rare things but also look for these discrepancies because we're missing what 95% of the universe. the standard model's great but but uh so so everything like this and then in the future there are many different ideas

28:44 out there what we want to do in the future beyond the LHC after I've retired for sure uh and and that you know includes electron positron uh colliders maybe a huge FCC maybe linear colliders also possible muon colliders for those of you in the muon business a lot of different ideas out there but precision is is is one of the things we really want to to look for so um be before we we we finish up actually I would like to to hear a little bit more from Simon about

29:12 you know what are the next steps you you mentioned getting more computing that's everybody wants that you know chat tpt will work better too with more computing

29:21 and we can use the same computers as the ones training chatbt so it would be great if they just hand it over to us hand over yes

29:29 uh yeah ask just ask chatbt could you hand over um but uh beyond that what else what other work can you do to improve move these models it uh what what work is going on

29:39 so really I mean there are two ways to compute this HVP contribution that is really carrying all the uncertainty and lattis QCD has only recently I mean last five years we were able all I mean to reduce our uncertainties by a factor of five or so and now we're really able to make this prediction

29:57 and we're very certain that we can improve but as as Claudia said as as soon as you want to get to get to better precision you always have to be more careful about tiny effects that you have to control.

30:07 So it's certainly getting bigger computers, getting better algorithms. I mean be smart about how you want to compute something.

30:15 Mhm. And also have have new ideas. And then there's a second way one can compute it has been done historically. It's called the Ratio method. And um if they I mean they can also improve with new experimental input actually.

30:29 Okay. because some sometimes a theory has to have for various values that you use for the input.

30:35 Um, okay. Before we go, uh, one last thing I'm gonna turn over to Fred here. What's next?

30:41 You said you're not going to do it yourself, right? Uh, are you turning over the handing the baton over to anybody else?

30:47 So, at Firmeny Lab, we still do have a few more papers to come out of our experiment. So, we're going to look at the potential for new physics to cause our result to change as a function of time. Maybe oscillating, getting a little bigger and smaller over time as a result of coupling to things like dark matter fields or violations of uh the postulates of special relativity. So, we'll be looking for that. We'll be looking for the electric dipole moment of the muon. we should be able to set a limit that's stronger than the current limit on how big that could be should be zero in the standard model. So if we were to see something that's not zero then that would be um exciting. Um but then the next muon gus2 experiment is going to be at J Park in Japan and they have a technique there that is um like ours but with muons that are not at the magic momentum. So they can't use electric fields to confine them.

31:46 Instead, they cool their muon beam to the point where they don't have to use electric fields and they can use a much smaller magnet. So, they will be able to do a complimentary experiment with smaller uncertainties. I should also point out that the reason that I'm here at CERN is to work on an experiment called muan that we're setting up at the CERN SPS. And so, what we are doing there is getting experimental input for a third way of doing the theory. So um you've heard from Simon about two ways right from electron positron collision data um the R ratio method and lattice gauge theory.

32:26 Well we're observing the hydronic vacuum polarization effects in the interaction between a muon and an electron when a high energy muon beam hits the electrons in a target. Oh

32:38 okay great. So I should say SPS by the way many people might know that super proton synretron which uh brought us the W and the Z beson many years back about 1983 I think it was way way back and we still use these and we have some older accelerators than that even that we still use as well. Well thank you very much. Uh Fred Gray is professor of physics at Regis University in beautiful Colorado I think it is. Um and uh Simon Kaberski and Claudia Krenella are both uh fellows here at CERN working on in the theory division. So thank you for joining us. This has been early morning coffee at CERN, a podcast by the scientists of CERN uh or not just CERN uh and and uh about the science of CERN. You can find all of our episodes on the CERN YouTube channel and anywhere you get your podcast.

33:33 Guaranteed. Go ahead. Find the place you get your podcast. You can find us. Be sure to do whatever you're supposed to do. Like and share and I don't know, send it to your friends. There's a lot of things you're supposed to do. So, do those things and subscribe. Um, our editor and producer today is Melanie Arnold. Hi, Melanie. Good job. Thanks. Um, our executive producer is Jacqu Fiche. Jacqu Fishche and Potraxic, also known as Jesus, uh on occasion, are our technical leads, while Ron is away getting fixed up. Our studio manager is Max Price. Um and sound engineering is by Potraik. Our original theme comes from the KET Blues Band with piano by Voit Play It Cryski. Uh many thanks to Paulo Katapano, uh Matthew Tomers, and Arno Morcelier for all of their advice and strategic planning. Big thanks to the entire uh education communication and outreach team here at CERN for providing us with access to beautiful

34:30 wire chamber studios and all the help that comes with it. I also want to take a moment to thank Cetna Krishna who's no longer with us. That sounds terrible because because uh she finished up her fellowship here at CERN. She along with Joanie Fam were really two of the people who came up with the whole idea of doing this and I get to have a lot of fun and I hope that they're doing well as well. Um, opinions expressed here are our own and do not necessarily uh reflect those of our colleagues or of CERN although we think they ought to. Um, my name is Steven Goldfarb. This has been Early Morning Coffee at CERN. We'll see you next month.

Questions about this episode

Who speaks in "Episode 6: A Final Moment for the Muon"?

Steven Goldfarb (Host), Fred Gray (Host), Claudia Cornella (Host), Zimma Kubeski (Host).

What is discussed in "Episode 6: A Final Moment for the Muon"?

In order: 0:00 CERN, muon g-2, Steven Goldfarb, Fermilab; 5:00 Fred Gray, LHC, South Korea; 10:00 LIGO; 15:00 QCD; 30:00 Steven Goldfarb, Fred Gray, Regis University; 35:00 Steven Goldfarb.

What is mentioned in this CERN episode?

13 people, works and ideas are mentioned, including Steven Goldfarb, CERN, muon g-2, Fred Gray, Fermilab, Claudia Cornella. Each one on this page links to its own page with every episode that mentions it.

How long is "Episode 6: A Final Moment for the Muon"?

The episode runs 35 min; the transcript is about 6,377 words in 96 timestamped sections.

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