Is the W boson too massive?

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Speaker 1: Hey, Daniel, I was wondering how heavy are the fundamental particles? Oh, man, is a really big range from very light to pretty massive? But like how heavy and how massive? Like? How can I get a handle on on these numbers? Well, one way to do it is to think about electrons like cats, I mean like electric cats. No, no, no, think about it in relative terms. If an electron was like the mass of a cat instead of its super tiny mass, then how heavy would a mu want be? While mu want is two hundred times heavier? Though, mue would be like a walrus? All right, Yeah, that's pretty heavy stuff. And your lightest quarks, the ones that make up the protons and neutrons inside your body, up and down corks, If the electron has the mass of a cat, and then the quarks would be about as heavy as a typical dog. I see, And does the light corks also chase the electron? They do, actually, but it's this pretty stable circle and they've been running in circles for billions of you, like a Tom and Jerry cartoon. But what about the top cork? I hear that one's pretty heavy? Yeah, So if the electron is a cat, then the top cork would be six blue whales. Yeah, that is bigger than a cat. It's three hundred and fifty thousand cats. Are the whales electric too, They're more positive? Hi am or handmate cartoonists and the creator of PhD comics. I'm Daniel. I'm a particle physicist, and I weighed the top cork for my PhD thesis. Oh did you really that was your Like the title of your thesis, I weigh one of the fundamental particles and this is what I found. Click to find out more. Yeah, so what if we are very curious about exactly how much mass each of these particles has? And back when I was a PhD student, the newly discovered particle was the top cork, and it was crazy heavy and everybody wants to know exactly how heavy was it. So my thesis and post stock work were like fancy statistical techniques to extract as much information as possible to get the mass of the top cork. Wow, it was a heavy burden. Did your thesis also weigh a lot? Like? Was it a thousand pages? It was a pretty massive topic. Yeah, was it printed in the size of a top cork? I thought at some point that I was going to collapse into a black hole during the writing of this thesis from all the snacks you were eating while you were writing it. As my thesis got longer and longer, I thought, what is the short style radius of a PhD thesis? Anyway? But anyways, welcome to our podcast Daniel and Jorge Explained the Universe, a production of I Heart Radio in which we put the whole universe on a scale to understand exactly what it's made of and how it's little bits work. Examine all the tiny, little moving parts to understand how they work, how much stuff they have, how they interact with each other, and how that all comes together an incredible chaotic dance to make the world that we know. Yeah, because it is a pretty massively cool universe full of giant, incredible things that defy our brains in terms of their size and scale, and also the tiniest, smallest things that you can even imagine. Some of these things are tinier than tiny, that's right, And that feeling you get when you look out into the universe that there are these really different scales that like, you are so much smaller than the Earth, and the Earth is so much smaller than the Sun, which is tiny compared to the galaxy. That same kind of thing happens also for particle physics. There are particles that are a million times heavier than other particles, and so we have this broad spectrum of masses. One of the great mysteries of particle physics is understanding exactly why that is. Yeah, the smallest of scales in our universe. There's a whole zoo of particles that not only exists, but that can exist and do exist sometimes in the universe, and they all weigh a different amount. And particle physicists really care about exactly how much they weigh because sometimes our theories predict how much they should weigh, and so if they don't weigh exactly the amount we expect, then we know something is wrong, something is new in the universe that we didn't understand, and sometimes that's a clue that reveals a whole new chain of discoveries. M isn't that a little awkward, though, Daniel, Like, what would you do if there were a whole bunch of physicists really interested in how much you wait or how massive you are? I would be flattered. I'm like, Wow, I'm so important to the universe. There are grants being written about me, Particle accelerators being devised just to accelerate Daniel and anti Daniel together. Physics paparazzi outside your house all the time, trying to shoot particles at you. Wouldn't that be kind of annoying? At some point over here, Daniel, over here, pep pep pew, they'd be like, don't have any more chocolate. We just spent ten billion dollars measuring how heavy you are. You just gonna change the answer. You can't just do that. Oh man, you have don't go on a diet for a lot, all of that literature, you know. The truth is I would hate to be the subject of so much scrutiny. I'm such an introvert. That would be a nightmare. But maybe you're making the point that we don't ask these particles if they want to be studied, right, Nobody got their consent to be part of our experiments. Yeah, what if they want to keep their mass private? Well? The interesting thing about particles is that they don't have mass as an individual property, Like I weigh a different amount than you do, and then every other person out there does. But particles all basically have the same mass if they're the same type. In fact, it's sort of the way we categorize particles, Like the difference between an electron and a muan is a muan is a heavier version of the electron. But all the muans out there have exactly the same mass because they're all part of the same quantum field. They're all just ripples in the same field. Yeah. Well, even taking a step back, it's sort of amazing that you can break down everything in the universe into like a short list of little, tiny particles, you know, sort of like the universe is made out of only five or six or nine lego pieces, and it's interesting that all these lego pieces are just a little bit different from each other. They not only have different like charges and quantum numbers, but they weigh differently. Yeah, and particle physics is all about finding those patterns, saying what are these particles have in common and what's different about these particles? And the reason we do that is that we're hoping to reveal some deeper layer of reality. We think that probably these five or six or twelve lego pieces aren't the fundamental nature of reality. They aren't the most basic parts of our existence, that they're more like the atoms we see that are made of smaller pieces, and that by arranging the fundamental particles and studying the patterns, we can get some clues as to what might be going on underneath. Yeah, and as you said, physics are really interested in knowing what the exact masses of these particles are because I guess you want to get the model right, right, Like if the model is off by even a little bit, you're wrong about the universe. Yeah, And because the masses tell us a lot about how these particles are connected to each other. Remember that when particles fly through the universe, they're new were just a tiny dot flying through empty space. They're flying through lots of quantum fields and interacting with those fields, and how they interact with those fields changes how they move, and that's part of how they get their mass. So by measuring the mass of these particles we can tell something about how they're touching all these other fields. So it's a very very sensitive probe of the particles and how they talk to the other particles. Yeah. And so if we've known about these particles for a bit of a long time now, and we've measured through mass. I mean, if you did it for your thesis, that must have been what like a hundred years ago, two hundred don't try to flatter me. Last year maybe, But they've been measured before, right, Like, that's one of the first things you did when you discovered these particles, when physicists discovered them, it was measure how much they wait, that's right, but it's a long project. First you discover the particle, you just know that it exists. Then you start to study its properties. One of the first things you do, is you said, is to measure its mass. The first measurements are usually very imprecise because you only have a handful of examples. You just discover this thing, is barely enough data to show that it exists. But as you accumulate more data and your techniques get fancy and fancier, then your measurements get more and more precise, and then you can start asking really interesting questions about like is the mask what we expected it to be? Doesn't make sense to us, Yeah, it doesn't make sense in terms of the theory that you have and firm the math right, and does it all hang together? Like there needs to be some self consistency right, right, And it seems like every time you do an experiment, you're refining that measurement, like you're adding more than the numbers down the decimal places of how much you how well you know this the mass of them? Yeah, And there's really two different ways that you can do that. One is just do more experiments. You get more data, and that can reduce what we call these statistical uncertainty, like the chance that you accidentally measure the wrong number due to a quantum fluctuation. But then later, once you have enough data, the real work is in understanding the data that you have to remove sources of bias because that becomes the dominant source of the uncertainty. So it can take years or even in decades before the final answer has come out about these measurements. Most precise results are sometimes arrived at ten years after the last bit of data was taken. Well, we've been doing this for a while, weighing the particles, and I think as in general, we've sort of feel that we or if we felt that we had a pretty good handle on what these particles weighed. But recently there's been some big news about or maybe big error about them that's right. Last week we released a paper to the world about a new measurement of the mass of one of the heaviest particles, a w boson. This is the particle that communicates the weak force and the CDF collaboration and group working at Fermilab where actually I was a post doc, so I did my research on that experiment, released a paper measuring the mass of this thing with unprecedented precision. Like the uncertainty they claim on their measurement is much smaller than anybody has ever achieved, so it should be a very very precise measurement of the mass. But the answer they got, the measurement they made of the mass, that number was a big surprise to everybody, and it made a big news. You were telling me that it was all over the science pages of all the major newspapers. That's right. It actually was the cover of Science, which is basically the biggest journal, and it was all over the news on. A bunch of listeners wrote in and said, hey, what's going on with this measurement? And also, hey, Daniel, I saw your name on this paper. What's up? What what's up? Indeed, so you're you're one of the authors of this paper. I am, in fact, one of the authors of this paper out of how many three hundred and eighty nine, three hundred and eighty nine authors? Was your position in there where you near the top or the bottom or is it alphabetic? It's alphabetical, so I'm always near the end of the list. Who goes after you? Mr uh xylophone. We have collabrators from all over the world, so we have every letter from the Hungarians whose names start with two a's to Chinese collaborators whose name starts with z h zough. I am not close to the end of the list, m Well. I In my field, at least when I was working on research, being near the end means you were more senior. So that's a good thing, right, It can be a good thing in our field, though we have this sort of ridiculous policy or anybody who has contributed in any way to building the detector or running the experiment is an author on every paper that uses that data, even if it comes out years later. I've worked on this experiment in almost ten years, but they still put my name on every paper, which is kind of ridiculous. Wow, So did you get to like type one word out of the whole paper or something. It's kind of embarrassing. But I didn't know about this paper until just a few days before the news broke. Really, it's like, hey, we're including you in this paper. You might win a no More prize. UM good life, f y I. It's sort of silly, and it just speaks to how like modern science is done in these really big collaborations and the publishing system hasn't really caught up to that. You know, authors sounds like a lot. But in my current collaboration on a list at the Large Hadron Collider, we have five thousand authors on every paper, and we publish more than a hundred and twenty papers every year. That means twice a week there's a paper going out with my name on it. I don't even know the titles of most of the papers that my name is on, and some of them I couldn't even explain the title to you. So being an author on these papers doesn't really mean that much. Then, how do you know it's good science? Like? What if they discover one of them, UM was not correct? Wouldn't that look bad on you? I think that's an excellent question, and I think in a perfect world, everybody who's an author in every paper should be responsible for the scientific content of that paper. I think that we know that that's not how things are working right now, and we need to revise somehow the way these authorship policies work. And I've actually proposed inside my collaboration that we do change that, that we don't have everybody being author on every paper. But there's a lot of resistance to that proposal. I guess there's some politics. But on the plus side, you probably get residuals and royalties right from these papers. You know that in science you pay to publish, right, You don't get paid to push. You get negative royalties exactly, Nobody. If you go google my name, I have something like more than a thousand papers with my name on it. Only a hundred of those are like my actual scientific output. Most of them are work done by my colleagues, and I'm sure it's all excellent. Well, yeah, that's pretty cool. And so this paper that your name is on was big news, and in fact it was massive news. And so today on the podcast, we'll be asking the question, is the w boson two massive? It feels like a very judgmental title here Daniel like, how can something how can something be too massive? Well, it has a higher mass then is predicted by the theory, and higher mass than other measurements. So their new result that came out is bigger than the previous measurements. It means if they're right, then the w boson isn't fat more massive than we thought it was and more massive than our current theory can explain. Well, I'm curious to see what happened. Did the w boson gain weight or with somebody leaning on the scale or something, But it's a very small difference, kind of right, like what was the old measurement and what was what's the new measurement? So the old measurement is quoted in weird units, which is why in the intro we talked about cats. But the units are mega electron volts, so that's millions of electron volts, and for calibration, about a thousand of these m evs are about what a proton ways. So the previous measurement of a w boson was about eighty thousand, three hundred and seventy mtvs, so like eighty point four almost protons. And now what did they measure it to be? The new one they measured to be eighty thousand, four hundred and thirty four, So it's an increase of about sixty four of these mtvs. I didn't quite spot the difference between the two numbers, about I'm sure to have phisic. It's a huge difference. It's a very small difference. You're right, you know, it's a difference of sixty four MTV out of eighty thousand. So it's very very precise. Issue is that the theory predicts it to be eighty thousand, three hundred and fifty seven with a very small uncertainty of about six. So the old measurement was eight three hundred and seventy and the new measurement is eighty thousand, four hundred and thirty four. Again, I'm catching the difference. I feel like it's maybe like maybe we can put it in terms of percentage. It's like point one percent different, maybe less. Yes, So the difference between the old measurement and the new measurement is less than point one percent relative to the ws mass M And I guess that sounds like a little but to a physicist that's um massive. Shall we say it's huge? Right, because if it doesn't match the theory, then there's either something wrong with the experiment or something wrong with the theory. Yeah. The key thing is not how big is this difference of sixty four mtvs relative to the WS mass. That's tiny. The key is to compare the difference to how well we know these numbers. The difference is sixty four mtvs in the measurement, the uncertainty is ten mtvs. So like they are very certain in this new measurement relative to the other measurement. So like the uncertainty is one sixth of this difference. All right, well, um, it's a big result and made all the news and and a lot of people ask you to come on the podcast and explain it, right, that's right. Folks were wondering what this meant for physics. Did it really break science like all those psyclon journalism headlines said, And so they wanted us to talk about it. Oh, man, I hope it didn't break science, because then we have to return it is science, have a warranty on it, or wait, we can return it was usually we were wondering how many people out there had heard of this headline and knew what it meant, what the difference between the W bosons mass could mean. And so, since this was a late breaking news event, instead of asking our cadre of Internet volunteers, I just walked around campus here at you see Irvine to see had undergrads heard the big news about the w boson? Yeah? And so you went out there into the campus and you ask people if they had heard of this interesting measurement and does it worry them? Here's what people had to say. Have you heard of the w boson? Only heard boson but not w um? What do you think it means if scientists discover that the w boson is a little heavier than it's supposed to be? I don't care. Have you heard of the w boson? What do you think it might be? Probably a policy in place for like an environmental aspects. And what do you think it would mean if scientists discover that some particle is heavier than it's supposed to be. Not so good? That's um not so good to be honest. And I've heard of the boson, not the w boson. Whatever. What do you think it means if scientists discover that the w boson is a little heavier than it's supposed to be. I'm not sure. Does it make you worried? Yes? Have you heard of the W boson? What do you think it is? Boson and shape? Look at you? And what do you think it means if scientists discover that it's heavier than it's supposed to be? Have you heard of the W boson? No? If you have any guess what it might be? Now my first year? No? Um, what do you think it means if scientists discover that some particle is heavier than it's supposed to be, it's more like charged. I don't know. Do you know what the w boson is? Have you heard of it? What do you think it might mean? If scientists discover that it's a little bit heavier than it's supposed to be, maybe it might be a bad thing. Does it make you worried? Kind of? But not really since I don't really know what it is? Thank you. What do you think it means if the W boson is a little heavier than it's supposed to be, the interaction length is a little shorter, Does it make you worried? M hm no, it makes me excited, all right. The question is do you know what the W boson is? No? I do not you have to guess what you think maybe a science law. I don't know. And what do you think it means? If scientists discover that a particle is heavier than it's supposed to be, it just didn't find it correctly last time? No, I don't you have to guess? What do you think it might be? Something with either physics or chemistry? Okay? And if scientists measure a particle and discover that it's more massive than it's supposed to be, what do you think that means? Maybe there's something else smaller than that particle. That's possible if it's bigger than we think it is. Okay, the w boson, I'm not familiar. If you have a guess a particle particle? Cool? And if scientists measure a particle and discover that it's heavier than it's supposed to be, what do you think that might mean? It's something unstable or that it's not functional in a normal manner? All right, Not a lot of people have maybe heard of this. Nobody had any idea of what I was talking about. Um, some people thought it was some sort of policy or some particles shaped like a W. I was kind of surprised. I thought the w boson was a little better known than that. It's only famous in certain circles a certain scales, like if you're really small, the w boson is big. Yeah. Well, I thought the w boson is going to get a W, but it looks like I got an L instead. Well. It's interesting because this time you went out into the campus, which is more of a maybe general audience than the one that you find online, because online you sort of get a lot of listeners of this podcast. Yeah, and I think that listeners the podcast probably have an idea of what the w boson is, but maybe don't necessarily understand why it's important to measure its mass and what this new measurement means and if we can believe it. Well, I guess to start with for those of us who don't know what a w bozon is, Daniel, can you explain it to us? Yeah, as you described earlier, we know that the world around us is made of tiny little particles and stuff that makes up you and me and the table in front of us. It's not smooth and continue us like it seems. It's more like a mesh with these little points of matter connected by forces, and so we've discovered but the little points of matter are made out of time, the little bits of stuff, and we call those matter particles fermions, like quarks and electrons. But there are also the forces that tie those things together. And those forces you can think about as communicated via field, like an electric field from an electron. You can also think about them as communicated via particles. So we call these force particles like ripples in those fields. And so for example, when an electron pushes against another electron, you can think about that is like ripples in their electromagnetic fields, or exchanging virtual particles. In this case it would be a photon. So every force that you know about has a particle associated with it, Like the magnetic field has the photon, the strong force has the gluon. The weak nuclear force, the weakest of all the forces we know, actually has three of these particles, the W plus, the W minus, and the Z. So there's sort of like heavier versions of the photon for the electroweak force, right, And I think this is something that maybe confuses a lot of people, or at least it confuses me. You know, this idea that you know when you take high school physics, or you know, even college physics. Do you sort of think of forces as just the some invisible things, like you know, the Earth is pushing me down through some invisible force, or you know, a magnet repels another magnet through some invisible force. But you're saying that, actually, what's going on. It's like they're exchanging sort of invisible particles when something is pushing against something else. It's a bit of a subtle question. We did a podcast recently about what is a particle? And one way to think about how particles push against each other is that each particle creates a field, and that field pushes on other particles. So when two electrons come near each other, each one has an electric field that pushes on the other particle. Totally equivalent, mathematically and philosophically. Acceptable way to think about it is, instead of feels, to think about particles being exchanged. An electron comes by another one and it shoots a photons at the other electron. On I think like photons, I mean I don't see light. I don't see like bright flashes of light between electrons. Well, these aren't things that you see, right. You can't see a photon unless it hits your eye. These are photons that are shot back and forth between the electrons, and sometimes there are a special category of particles we call virtual particles that don't follow all the same rules that normal real particles that you observe do. If you're interested in the subtleties there, we have a whole podcast episode about what are virtual particles? Right, It's interesting that, like you know, the force that one magnet pushes on another magnet is basically the same thing as the light that hits your eyeball from the sun. Right. It's it's sort of hard to square the two, but they're the same thing because one feels tactile and the other one feels visual. But they're the same thing. They are the same thing depending on your definition of same thing. They're all part of a larger phenomenon, which is electromagnetism. There can be different aspects of it. It's like saying our electric fields the same as magnetic fields. Well not exactly, but there are two sides of the same coin, and so in that sent they are the same. Every force that's applied via electromagnetism is communicated via electromagnetic fields, and all information that moves through electromagnetic fields you can think of as photons, like every ripple in those fields, every piece of information with the field, was one way and now it's another way that you can think of as a photon M. And so the photon is basically the thing that carries force, or the electromagnetic force, and so the W boson is one of the things that carries the force for the weak force, which is one of the fundamental forces. Exactly, the weak force is one of the fundamental forces. And it actually has three of these particles that carry its forces, which seems weird, like why does it need three? It's busier, you know, it needs more staff, it needs three sort of because we've already done some unification, like we found the W plus, we found the W minus, we found the Z, and we realized, oh, these are actually all part of the same thing. Originally, people found the Z and the W separately and they're like, oh, these are different phenomena until scientists put them together into one idea called the weak force. And so those sort of fit together very nice as part of the same force. So we have those three particles, the W plus, the W minus, and the Z that we now call carriers of the weak force, the force particles for the weak force. Okay, so this one is a force particle. Does that mean that we're not actually made out of W bosons or is it somehow sort of these things trapped inside of me. It's another great philosophical question, right there are w bosons inside you right now, because there are particles that are feeling the weak force. Right some particle potassium, for examples, decaying radioactively right now from the banana that you just ate, and that's happening via the weak force. So there's a W inside you right now. Are you made up of w's is a little bit harder to say, Like, you're made up of the matter that's inside you, but a lot of your mass actually comes from the energy and the bonds inside that matter, Like your matter comes from your protons, but the mass of the protons mostly comes from gluons inside you. So I would say that you are made up of those matter particles, and also the force particles definitely need them to make up Jorge M. Yes, and that's important for sure, especially um bananas. So then is the W boson helping keep me together? Is this something that sort of helps things you know, stay as one piece or does it only happen when things decay or things break down. The W boson is part of the weak force, and it's really really weak, and so it doesn't play a role in holding together quarks into protons and neutrons, and it doesn't play a role in terms of holding the atom together like electrons surrounding the nucleus, and so it doesn't really play a role in holding things together. It mostly plays a role when things break down, When a neutron decays into a proton, for example, that happens via the weak force. M I see, all right, well, but it's still important because, you know, it tells us a lot about how things breakdown, which is kind of an important process in the way the universe works. And it's also important because it's a cousin of the photon. The WS and the Z are actually very closely related to the photon. They're just sort of like heavy versions of the photon. And the way that we group those three particles together, the W plus W minus and the Z into the weak force, we can actually include the photon into that, making a quartet of force particles that all fit together really beautifully, and we call that unified force the electro weak force, where we combine electromagnetism and the weak force into one idea. I see. So it's only famous because of its cousin. That feels a little nepotistic there. It's part of the entourage of famous. It's the guy who gets the water whenever the the photon doesn't roll without the woveson. Alright, Well, it's one of the fundamental particles, and it's important because it's in particle interactions, and it helps define our theory of the universe. And so recently scientists measured it to be different than we thought it was. And so let's get into that measurement and what it could mean. But first, let's take a quick break. All Right, we're talking and discreetly about the w bosons mass Daniel. I guess there's a lot of interest in knowing how much this thing weighs. Do you think the ws out there are blushing? Can? Can't? Do they have color? Do they have color charge for them to turn red? No, you're right, they are colorless. They are colorless. They're they're colorless. Maybe they don't care. All right, So there was a big headline recently that the mass of the Dewey boson is heavier, is more than what we thought or what the theory predicts. And so Daniel, I guess maybe a more basic question is why does the force particle need mass? War isn't it just transmitting forces? It doesn't need mass, And a lot of the force particles don't have mass, right, the photon doesn't eight gluons and none of them have mass. But this particle has mass. It doesn't need mass, and we think back in the very early universe it didn't have mass, but then it got massive because of the Higgs boson. Interesting, so it doesn't neat mass, but it somehow has mass, and it's all because of the Higgs boson. It's all because of the Higgs boson. Exactly. Remember how the photon and these particles fit together beautifully into this nice quartet, and they'd be this very nice symmetry. For those of you interested in the mathematical details, it's a gauge symmetry where you can like rotate these particles into each other and it preserves all sorts of interesting properties. That only works if these particles are all massless, if none of them have any mass, And we think in the very early universe that was true, and the W and the Z had no mass, and they flew around the universe just the way the photon does. And in fact, we think the weak force was much stronger because it's particles weren't so massive, so they could fly further and interact more. But then the Higgs boson came along and it broke that symmetry. May have heard the phrase electro weak symmetry breaking, that's what this refers to. It made the ws and the z s very heavy, and it left the photon massless. M Yeah, I guess it's kind of weird to think of a force particle as having mass because first of all, um that means it's it's slower, right, like it can't go at the speed of light. And two does that mean that it's like costs you to exert a force, you know, if you have to use mass or where does that mass come from? If you are pushing one thing from another with the weak force, it definitely costs you. To create ws and zs is harder than it is to create photons. That's why it took us longer to discover them. At colliders. The WS and disease were only discovered in the eighties at certain we had enough energy and colliders to make them. And then if you don't have enough energy to make them, you can make them as virtual versions where you like borrow the energy temporarily from the universe to make this heavy particle. But the heavier the particle is, the less likely you are to be able to borrow that energy. So to like borrow enough energy to quantum fluctuate a w out of the vacuum is much less likely than it is for lower mass particles. Is that where the name weak force comes from, because it's sort of like it's really hard to do, so nobody ever uses it. Kind of that is why the weak force is weak, because it's particles are massive exactly, and it also means that it doesn't have a lot of range, right, Like if something has mass, it eventually decays, and so like you can't shoot a boson from here to the Mars because it's not going to get there. Yeah, the universe likes to spread out its energy. It doesn't like to have a lot of energy density in one particle, and so if a particle can decay to less mass particles, it will so The reason your electrons are stable is because there's nothing lighter than an electron that they can decay into. But a W can decay into things, and so it will very quickly. Like a W naturally lives for ten to the nineties twenty five seconds. What so you have ten to the minus twenty five seconds to measure its weight. We'll get into the details. But you can't actually weigh w's directly, and you can't see them directly. Well, all right, well that sounds like a perfect transition here to talk about how you do measure the mass of a force particle if it's so hard. Well, the first thing to understand is that you don't measure its weight, right, you measure its mass. The difference there is that weight is the force of gravity on an object, or mass we think of as an inherent quantity. Although you can get into whole philosophical questions about what is mass and where does it come from? The mass is something that you have even if you're not in a gravitational field. Right, So you would weigh different on Saturn than you do on Jupiter than you do on Earth, but your mass is the same. So that's the quantity we're interested in your trying to measure not how much it weighs on Earth, but like how hard it is to get it accelerated, or how much energy it costs to make this mass? Right, yeah, how much inertia it has? How much it been space. The other problem is that you can't really use gravity to measure these things. Like if I asked you how massive is that bag of onions, you would put it on a scale you would use gravity. You would say, I know how much gravitational force there is on it, so I can deduce what it's massive. Now I would just mash it against another bag of onions. Physicist, you're a natural physicist, now exactly, make some freakasy or something exactly. And so the reason we can't do that with particles is that they don't weigh very much. You know, these amounts we talked about earlier are tiny, and so the gravity pactional force on the w bson it exists, but it's basically impossible to measure even though the w is one of the most massive particles, And so instead we don't measure its weight, we measure its mass. All right, Well, then how do you measure its mass? Well, we would love to measure its mass by seeing like how it moves, so we can measure it's inertia, right, But we can't do that either, because, as we said before, the W doesn't last for very long. When we make it in our colliders, it lasts for ten to the minus twenty five seconds before it decays into other stuff. And so because we can't ever see the W directly, all we can do is look at that other stuff the W turned into and try to reconstruct what its mass was, right, because I think the other particles that do fly for a while, you can see like how much they bend in a magnetic field and things like that, and that kind of tells you it's momentum, which tells you it's mass, right exactly. So you use equals mc squared and you say, well, the mass of the W boson is getting converted into the energy of these other particles it turns into. If you have some particle that's really heavy but you can't see it directly, it doesn't last very long. It turns into other particles that you can see. Then you can measure the energy or the momentum of those particles, and from that energy you can reconstruct how much mass the original heavy particle had because its mass is getting turned into the energy of those particles. Be like trying to see how much Daniel whites and ways by weighing your kids. Sort of, It's more like measuring the brightness of a nuclear bomb and using that to figure out how much fuel there was, Like what was there before things broke apart? Exactly? If I took all this energy that was released and asked how much mass is that equivalent to, then you're weighing the mass that was converted into energy. So that's what we're doing with the W. We're seeing the parts that fly out the decay products of the W. We're measuring their energy or their momentum, depending on the particle, and we're using that to figure out how massive the W must have been. Well, that sounds straightforward, but there are difficulties, right, It's tricky. It is tricky, and one reason is that the W doesn't always decay to visible particles. The way they measure its mass is when the w DK is to a muon and a neutrino, and the MU one you can see it flies to a detector. It bends in a magnetic field. You can measure that bending so you can deduce the momentum of the muan. The neutrino, however, flies right through your detector and you can't see it. It's invisible, So that makes the problem a little harder. Yeah, I guess you need all the pieces to get a good rectorate measurement of what the thing looked like when was put together. Right, if you're missing a piece, then you're not gonna be able to tell how much the thing. Wait, originally it makes it harder. You can do a better measurement if you have all the pieces, but even if you have half the pieces, you can still make a measurement. Like imagine you could only see half of a nuclear bombs explosion. The fact that you know you're seeing half of it means you can extrapolate to the other half. Right, as long as you know what you're missing, you can guess what might have been there. So they measure the mass the w just by seeing one of these particles that flies out. But then do you sort of need to know what the missing particles parts are, right, And that's where your models come in. That's where a lot of our models come in. And that's where a lot of the really careful experimental work comes into figuring out how to do this very very precisely. Yeah, because there's a lot of like uncertainty, right, and so you need a lot of data to make sure that what you're measuring is correct, right. Yeah. You want to see a lot of examples to make sure you're not seeing anything weird, any random fluctuations. And in the latest measurement they had four million examples of w boson is decaying either to an electron or into a muant. But that's not really the problem. That challenge these days is not getting enough examples of ws. They think they have enough. The challenge is making sure there aren't biases. Like when your muan flies through its magnetic field and you're using its curvature in that field to measure its momentum, are you sure you know exactly how strong your magnetic field is, as one of your magnets that makes that magnetic field slipped by one millimeter in the thirty years since some grad student installed it, how would you know? And so it's that level of scrutiny, that level of detailed understanding required to a precise measurement of the mass of the W right because I guess if your instrument is off, all of your results are going to be off, right, Like if there's a blur in your microscope, you're going to think that, you know, what you're measuring has a blur in it, exactly. And that's why this measurement has taken so long. You know, they stopped collecting data in two thousand and twelve and this measurement came out. Now, it took them ten years to understanding gory detail exactly what does that magnetic field look like? How does the detector respond? They did things like looking at cosmic rays muans from space to see how they fly through the detector to understand exactly where every piece of it is down to the micron. Wow, that would sort of drive me crazy, right if you have to worry about, you know, your experiment, which is huge, but you have to worry about it down to like the particle level, Like are all the particles in my instrument okay? Or are they somehow being you know, shaped or moved by some cosmic fourth. Yeah. And it reveals something cool about these experiments, which is that there are very different kinds of physics you can do. There's the folks who are like, let's look for an exciting signature or something new that if we see it, we know it's there, and it's like a big press release. And there are other folks are like, I want to very carefully understand this one particle to gory detail. Even if it cars ten years of super fine understanding of how the detector works, it's just sort of like a different way to do science. And so I imagine that people have been working on this for you know, decades, and they've been refining this measurement of this one particle, and they've got some new results out a few days ago. That's right, they did, and their answer shocked the world. All well, let's get into this massive shock, this massive discovery about the w boson and what it could mean. But first let's take another quick break. All right, I know, so who got to tell the w boson that it weighs more than it should? Well, maybe the w boson is like you. It doesn't read science, so it doesn't know you're gonna say. It's like me, who doesn't care how much their way. Hope you could all be so lucky. Maybe the w is listening to this podcast, and this is how it's finding out. Oh no, that would be awkward. Sorry, you look great, boon. So they did the big measurement. It's sort of it's a new measurement, right, or it's something they've been measuring for a long time and only just now they published the results. Yeah, and if you might be surprised to hear that this is not a measurement that's coming from CERN, it's not from our new fancy collider, the Large Hadron collider that discovered the Higgs boson. This is from the previous generation. The last champion, the Tevatron just outside Chicago, which has the energy of about one seventh the Large Hadron Collider and turned off in two thousand and twelve. But they've been biding their time and working carefully on this measurement for ten years, having just released it. Wait what they did their measurement back in twelve, and they've been just processing the data for ten years. The last collisions were in two thousand and twelve. And yes, they have been processing the data and analyzing it and thinking about how to bring down these uncertainties and measuring the location of the detector and calibrating it and double checking it and double checking those double checkings and then hiring somebody else to independently cross calibrate those double checkings. Oh, I see, Like, if you find that there's a bias in your instrument, you don't fix the instrument, You just fix the data to account for it. Well, they spent the last ten years developing these tools to measure the w boson and to get the answer. They didn't know what the answer was until very recently. We do this thing in particle physics where we blind ourselves from the answer to avoid biasing ourselves. We don't want to change the way we're analyzing the data to get the answer that we want or the answer we expect. So they actually added a random number to all of their data so that nobody who was working on the analysis would know what answer to expect. And they only unblinded it. They only removed that random number in just about a year and a half ago. Wow, that's wild. So they like corrupt the data so a little bit right, so that you don't like look for the like, you don't manipulate your analysis to get the answer. You're like, you're supposed to work in your analysis independent of what the data says. And we're not worried about like explicit manipulation where people are like fudging the results. We're worried about like subtle biases. For example, if you get the answer you expect, you stop looking for mistakes, whereas if you get the answer you don't expect, you keep looking for bugs. And so what happens is people just leave bugs in if they cancel each other out, or they leave bugs in if they've given the answer they expect, which might not be the right answer. With his history and particle physics of experiments confirming previous experiments, and then we discover later, oh, all those experiments were actually off by a big factor, and then the result jumps. So we have to be very careful because we only have one shot at this right. You can't run the collider for ten years again with one data set. You have to do it right in an unbiased way. So we hide the answer from ourselves to avoid being biased by what we expect to see. M M. That's wild. It's will that you would do the experiment and then just kind of sit on the data or working for ten years. You know. I think as part of the public, you're sort of used to this idea of like scientists in a lab and she's measuring something and she goes, yourek, the results are there, but here it's like they do the measurement and then ten years later it's like, oh, hey we found something. Yeah, well, most of the people left this experiment. This experiment used to have like five scientists on it in it's heyday, and then the large hage On collider turned on and almost everybody moved over to the LHC to work at CERN. But a few folks stayed behind because this measurement would take a long time and a lot of really careful work, and they thought it was worth it. So there's just like a few folks left and most of the lights are off, and they're like wrapping up the last little bits of science you can do with this data, right right, And I guess it's tough because it's not like you can ask them to do it again, right, not like, oh, you found this that's interesting. Can you run it for me again and see if we find it again? You can't because the thing is like ten years old. It's been decommissioned for ten years. M it's in pieces, literally, like it doesn't exist anymore. They've built a museum where it used to be. Wow, all right, well what did they find? What was this exp remant that they did? So the experiment is the collision of protons and anti protons. So the experiment uses the Tevatron collider, which smashes protons and anti protons together at two trillion electron bolts and that's one seventh the energy of the large Antron collider, and it's different from the LHC. And then it's protons and anti protons instead of protons and protons, which is what the LHC collides. Really you can make anti protons, yeah, and it's hard, which is why they didn't do it for the late C. But at the Tevatron we fabricated anti protons by smashing particles and basically a big blob of rock and filtering out the anti protons that come out the other side. Not very easy to make them, or to store them, or to insert them and accelerate them. It was a huge piece of work, and kudo to the accelerator engineers at Fermula who made that work. Yeah, it's pretty cool. I guess they're very ordinary, right, because they're very anti everything. They're not protons exactly. There antons antons. Well, I guess what I mean? Is is this an experiment similar to the large hadron collector? Like, is is it about, you know, spinning protons around in a ring and then you spin anti protons I guess the other way in the same ring, and then you bring them together. It's similar in idea to the l e C. You have a ring, you're accelerating particles around it. A few points around the ring, you smash those particles together to create collisions. So here you have protons going one way and anti protons going the other way. And so you need two different rings because you don't want the protons and antiprotons just smash together except at the heart of your detector. But you can't actually use the same magnets because protons going one way it bent the same as anti protons going the other way. So that was a clever trick. And so you smash a bunch of these a lot, and then you look at kind of what comes out of it, right, and mostly what happens when you smash protons and antiprotons is a big flash and a lot of quarks flying out. Because quarks are created by the strong force which is the most powerful force, and so it's the most likely thing to happen. The weak force is very weak, and so it's interactions are much rarer. But sometimes what happens is you get a down cork from one particle and anti up cork from the other, and they come together to make a W minus. Where you might get an up cork from one side and anti down cork from the other come together to make a W plus. That happens very rarely in billions of collisions, and you filter those out and you get a few million examples after running from like ten years. Wow, and so how long did they run this experiment? This data set is about ten years of running that ended in two thousand and twelve. Wow, wait they ran it for ten years and then it I guess that makes sense now it took him ten years just to go through all that data. Well, it takes ten years just to get the data, just like do the collisions and find those ws, and then another ten years to analyze it, to go through it and to get the answer. So from start to finish, it's twenty years. It's ten years of data taking and ten years of data analysis and how long to build the thing that wasn't mean also like ten years, right, Oh yeah, that was ten or fifteen years. They started that even earlier. That's back when I was a baby. So this whole projects like as long as my lifetime. That's wild, Okay. So then you look at the brief from this these collisions and somebody you pieced together the measurement of the w Boson mass, and I guess what did they find? So what they found was not what they expected. All the other experiments in the world has measured this, The LHC has measured it, Other experiments that Tetron have measured it, experiments from other colliders have measured it, and they all came up with an answer of eighty thousand, three hundred and seventy. That was the previous best measurement of the w boson mass okay, eight three seventy, eight three seventy. And people were pretty happy with that number because it agreed with what the theorists predicted. The theorists go into their offices and to sit down with calculations, and they say, the W boson sometimes interacts with the Higgs and with the top and we know the mass of those particles, how heavy should the w B, and they do all their calculations and they come up with a number, and their number was eighty three fifty seven. So the old measurement was eight three seventy and the expectation from the theorists was eight three fifty seven. Those are pretty close. People were pretty happy. Yeah, and like you said, it came that three seventy came from multiple colliders, right, Like you know, they measured it in Geneva, they measured it in Japan. And now this new measurement was four thirty four with an uncertainty of just ten. So not only is it like sixty mtb above the theory, it's like above the other measurements with an uncertainty of just ten. So the result is shocking, not just because it's so much heavier than the previous measurements, but because it seems so confident. They're like, oh, yeah, it's heavier, and we're very sure it's heavier. Well, as we've learned from us politics, being confident doesn't mean that you're right, though, doesn't it. Yeah, Well, there's a difference between physics and politics, and this is one of them. It's kind of an interesting scenario. So you're saying that, like the theory predicts through fifty seven, most of the people who have measured this measured this to be three seventy and they were all independent, right, with different colliders. But now this new measurement is way higher. Wouldn't you just say, like, there's something wrong here? You it? But this measurement is also the most precise of all the measurements we've made. This one claims to have the best handle on all of these details that affect the mass of the w. So on one side of the room you have a bunch of imprecise measurements saying one value. On the other side of the room you have one very precise measurement claiming something else. And so it's a puzzle. Yeah, I mean some someone must be wrong kind of a right. And it feels like this one's out there in the corner of the room by itself, whereas everybody else is on the other side. If somebody could be wrong, or it could be random chance, and you can ask the question like, well, what's the odds of a random fluctuation? You know, these are quantum particles we're talking about. Sometimes as new ones end up a little faster in the w looks a little heavier. That can happen. There's always statistic but they calculated what are the odds of the w boson having the mass the theory expects, and then see DF measuring this, and those odds are one in ten to the twelve. So it's very unlikely to be like a random fluctuation, right, Yeah, I mean, I'm sure that's what they got, But I guess there's a skeptical you know, engineer, you could you know, if you're out there in the middle, in a corner of the room by yourself, maybe late there was something wrong with the equipment or something. What's the certainty that they didn't make a mistake. It's a bit hard to pull apart. Like, on one hand, I know these folks. They are the most careful scientists I've ever met, the kind of people where if you show them a result and there's one tiny little part of it that doesn't make perfect sense, like what's this wiggle over here, they will not let it go, and they will go down a rabbit hole for months to understand it. It It can be very frustrating to work with these people because they are so detail oriented, and that's why it took them ten years because they did so many insane cross checks just to make sure they didn't mess at all up. So they have a lot of credibility. On the other hand, their result disagrees with everybody else, and so you've got to wonder if there's something that they haven't understood. And one area to look at is like this claim of their precision. They're claiming this measurement of four thirty four with an uncertainty of about ten. Some people have wondered whether that estimate is accurate, if in fact, they really understand those uncertainties as well as they think they do. And it's not about them making a mistake in any one cross check. It's about how to arrive at this small uncertainty and then what that means. For example, they had many sources of uncertainty, how do they combine all of those two? I mean, if you have two uncertainties of five MTV, what's the chances of getting a ten MTV fluctuation? The answer depends a lot on whether those two sources tend to fluctuate together or tend to cancel each other out. And now we're talking about understanding how likely a sixty MTV fluctuation is with lots of sources of uncertainty that are all around five MTV. To say that you know how likely that is means you think you understand the rare events really well and whether they fluctuate together or cancel out. So I think the result is probably right, but the uncertainty might be underestimated, or the calculation of how unlikely we are to get this big a deviation might be a bit overstated. So in that case, the result might not really be in that much tension with the other results or with the theory results. Right. Well, I mean, I'm not trying to, you know, throw down under work. I'm sure they're top notch and they're amazing scientists. I guess maybe the maybe the question that is on my mind is like, well, what could have been wrong with the other measurements? That would you know, what could be the reason this one is so different? What could have been wrong with the other measurements? You want to cast out on their qualities as a scientistic what I'm saying, I'm saying is this new measurement is doing that, and what are they saying could have been wrong with the other ones? Well, so they're not analyzing the other ones and criticizing them. They're just coming up with their measurements saying here's what we got. And they did a lot of really important and impressive cross checks, like they used the same method to measure the mass of the z bos on those z ways about these mtvs, and just as a cross check, they're like, let's measure the mass the z and they got its spot on, agreeing with everybody else. So there's a lot of reasons to believe this, but as you say, it disagrees with the other measurements, and we don't understand that. The truth is, we don't understand and the discrepancy between these experiments, there's two different important discrepancies. There's this new CDF result is different from what the theory expects. It's also different from the other measurements, and those are two things that we don't understand. I see nobody's saying nobody's wrong, anybody's wrong. They're just saying like, hey, I know you guys did this, but this is we did this, and we worked hard, and this is what we found. Let's let's all sit together and figure it out. So now we sit through it and try to think about it and try to understand where things could have gone wrong, or if this one's right, what it means about particle physm Right. Yeah, I was gonna say. The science headlines were not so measured. They're like, oh my gosh, did we break science as everything we thought was right as it turned out to be wrong? Right, It's that's sort of how this has been kind of portrayed in the media, right, like maybe we've been wrong all this time. Yeah, the most exciting way to read this is, Wow, this new measurement is right, and it means that the theory is wrong. That means that the prediction of the w mass to be lower than what CDF just measured means that those predictions are wrong, which means that all those fancy calculation is about how w bosons and mid virtual top corks and Higgs bosons those must be wrong, which means there's something wrong in our theory of particle physics. If this new measurement is correct, I see, and so I guess what specifically could have been wrong with our clearly wrongular theory about the universe that this measurement exposes. The great thing about these kind of measurements is that they're very general probe like, these masses are sensitive to the existence of basically every particle out there. Remember the muan gm is to measurement we talked about recently. You did that really cool cartoon about the reason that's so powerful is because it's sensitive to the existence of all these other fields out there that it can interact with. And the W mass is the same way. When it's flying through space, it's sensitive to the existence of new particles we don't know about that might change its mass. So what this means is there might be other particles out there that make the W mass different from what our calculations assume. Our calculations use the existence of all the particles we know about, but if there are more particles out there, you would get a different W I see. Yeah, it's sort of like the zoo analogy, right, Like, you know, we have this Zoo diagram of all the particles, but if something's off, maybe it means that, you know, the panda is sprouting off a little rabbit on the sign and the nobody had noticed before. Yeah, Or if you're feeding the panda three square meals a day and it's still gaining weight, maybe somebody sneaking at some snacks and you weren't. Whatever, maybe some some physicists who are overly interested in its weight I've been snagging or helping it out, yeah, exactly. Or maybe the clever pand is sneaking out of its cage at night and helping itself to the vending machine. There you go, mystery solve. But I guess it's sort of points to this idea, and I think probably the reason that it got so many headlines is that, you know, everyone is interested in this idea of like, you know, we have this model of the universe. Maybe we've been wrong all along and it's a little solahous, but it has happened in the past, right, It definitely has happened in the past. And you know, there are two different ways to discover something new about particles in the universe. One is like actually see some new particle like the Higgs boson, and be like, look, here's something new. We found it. Another way is to just do a bunch of consistency checks between the particles we do know and see if they all add up, because if they don't, it means that there must be some particle out there playing on the field. That you're not aware of. So it's a little bit more indirect, but it's also a little bit more general, So it's a nice way to cast a wide netancy. Is there something new out there? And we would love to discover something new because it would help us understand all the open mysteries of particle physics. Yeah, and I guess it sort of takes a little bit of courage to do that, right, Like if you know that everyone is saying one thing, right, they have this measurement of the w boson it's matches the theory. You know, it takes a lot for sciences to go like, hey, I'm measuring it to be different, to just sort of stick your head out there and say, hey, maybe it's different than what everyone thought it was. And you know, they've known about this result since November twenty twenty. That's when they remove that random number and actually saw the answer for the first time. And they kept it to themselves in a very small circle of folks while they worked for a year and a half and just double triple check all of their double checks before they went out there in public with it. And I'm sure as you, as one of the authors, got to double check it right. No, I wasn't even aware about this until two weeks ago, so they kept us to a very small circle. Otherwise, you know, it would have been on the podcast a year ago. Folks would have been the first to hear, right, right, Yeah, Daniel, what's what's going on there? You though you have connections? We should have been ahead of this story. No, I got the paper a few days before it was released, everybody else under embargo. Yeah, and I guess you also never know what's going to capture the imagination of the public, right and the newspapers. Right. Sometimes I feel like, you know, some these discoveries are seemed like they're the amazing and revolutionary, but hardly anyone notices. Yeah, you can never tell what people are excited about. But particle physicists at least are excited. You know. The day after this was announced, there was a flood of new papers put out by theorists explaining this new result. They have some model where the Higgs boson is made of other smaller particles it's not fundamental and that explains the w boson. Or they have a model with some new crazy particle they call a sweet no particle like a weird supersymmetric version of the w boson and now it explains this. So now that we have this new result, the theory community is going wild coming up with ways to explain it. Well, I guess that's sort of how signs works. You know, it's in a continual process where people are coming up with new ideas, new measurements, and you gotta, you know, don't take the established facts as established sometimes exactly. And if you trust what you've done and you double checked everything, and you've got to come out there with your answer even if it flies in the face of other measurements, because hey, maybe you're wrong or maybe they're wrong. History will sort it out, all right. Well, best of luck to the scientists working on this, and then I guess stay tuned to see who is not right. But you know who has the most to say about what's the mass of the w boson? That's right. We'll keep working on it, will make measurements of it at the Large Hadron Collider and and at future colliders, and eventually we will know the truth. Yeah, we will know if Daniel was actually working on this or not. To be surprised even to himself. Well, we hope you enjoyed that. Thanks for joining us, see you next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of I Heart Radio. Or more podcast from my heart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.