How do we measure the Higgs boson mass?

Published Sep 7, 2023, 5:00 AM

Daniel and Jorge talk about why the Higgs mass is such an important number and how physicists weigh such a fleeting particle.

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Hey, Daniel, I have a rude physics question.

Oh no, not another dark matter poop joke.

I hope, I think we did that one already.

All right, then, shoot, all right?

Is the Higgs boson heavier than expected?

Are you asking if physicists think the Higgs is like two round? That is a bit rude.

I'm talking about it's mass, not its volume.

Maybe the Higgs doesn't just give mass to other particles, it gives them muscles.

What like the Higgs is the steroids of the universe? Is that legal?

Lots of physics? Say yes.

I am Warhamm and cartoonist and the author of Oliver's Great Big Universe.

Hi, I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I feel like my density increases every.

Year, density of knowledge or density of chocolate eating, like your chocolate cores is getting bigger.

Well, those two things are tightly correlated, so I'd say yes to.

Be What do you mean like chocolate gives you knowledge.

Well, there's definitely a correlation between Nobel Prizes one and chocolate consumed per capita.

Oh interesting, But which one comes first?

We don't have to get into correlation versus causation when it comes to chocolate.

I think we do. I mean it makes a big difference. Like if you have to eat a lot of chocolate after you win the Nobel Prize and you kind of have a lot of work to do.

All right, let me go get some chocolate and then we'll figure this out.

No, no, no, that's the whole point. You should maybe figure what's the causation here.

I can't figure anything out without chocolate. It's my superpower.

Then you're in a paradox. What if you need chocolate after you win the Nobel Prize, but you can't win the Nobel Prize until unless you eat a lot of chocolate.

What if I opt for a Nobel price that's not gold, it's just gold foil around bad chocolate.

That doesn't fix your paradox, though maybe it may just means it's impossible. But anyways, welcome to our podcast, Daniel and Jorge Explain the Universe, a production of iHeartRadio.

In which we dig into the apparent paradox of our universe. It is both mysterious and bizarre, and yet somehow also understandable. Working carefully at the cold face of knowledge, we can hammer away at it and slowly build up an understanding of how this universe works from its tiny little quantum part articles that weave themselves together to give us this reality we know and love.

That's right, the universe is deliciously perplexing. It's dark, and it's velvety smooth, just like chocolate, which means we can't get enough of it.

And it is massive. Not only is it very, very large, but it's also filled with a lot of stuff black holes and neutron stars and just normal stars and rocky planets and maybe squishy little beings crawling on their surface.

And thank goodness it has squishy little beings like us, because we're here to ask questions about it, and we do that here on the podcast, where we tackle the big unknowns about how this universe works and why it is the way it is.

And often on the podcast we're telling you about the things that we have learned in science. But one of my favorite kinds of episodes are the ones that dig into how we figure it out, how we know what we know, rather than just swallowing the numbers that's signedis give us. We want to unwrap them and figure out how exactly they measured this or that to be whatever number it is.

Yeah, because there is a lot to know about the universe and a lot that sciences figure out, and it's interesting to dig into how it is that we know these things. Sometimes the story is maybe even better than the facts that you've learned.

Experimental science is not just go out there and check the theoretical predictions. Sometimes the theory doesn't make any predictions, and it just says, we don't know how heavy this thing is. Go measure it, and measuring it requires inventing all sorts of cool and clever tricks. That's what experimental science is all about, and we like to celebrate that here on the podcast. We've had fun episodes about all of the inventiveness necessary to measure the speed of light, or to measure the gravitational constant.

Or to measure how much chocolate. Physicists can eat safely.

Data says there is no upper bound.

Really, that doesn't sound like a scientific statement. I think science is pretty clear there is a limit to how much chocolate you can eat.

I don't know. I haven't yet collapsed into a black hole, but that may be in my future.

I guess it's hard to prove a negative or a maximum m hm.

Really the question is if you eat a lot of white chocolate, you turn into a white hole or a black hole.

So to be on the podcast, we'll be asking the question how do we measure the Higgs Bosons mass?

Right? Did you say mass or math?

I think I said mass right, So we do.

Have to use a lot of math to figure out the Higgs Boson mass.

Of course, does a Higgs Boson have its own math?

As far as we know, there is just one math. There is the math. But everything has its own mass, and it's an interesting puzzle to figure out why some particles have a lot of it, why some particles don't seem to have a lot of it, and to learn about exactly how we measure the mass of these tiny little particles. You can even just barely see.

Well, some particles don't have any mass, right.

Yeah, that's right. Photons have no mass, Gluons have no mass. Gravitons, if they exist, probably have no mass as well, mass isn't even a necessary attribute, Like you can be a thing without having any stuff to you.

Right, Although, as we've talked about many times on the podcast, the question or the idea of mass is kind of a tricky one, right, Like there are different kinds of masses, and also like what you might call mass is not necessarily the stuff that you have about you.

Yeah, our intuitive understanding of mass is different from the sort of mathematical physical description of matter at its most microscopic.

Well, this is an interesting question because the Higgs boson is a pretty big deal in the universe, right, I mean, it was discovered a few years ago and people were very excited because apparently it is a very important particle in the pathion of particles in that it gives mass to other particles.

Yeah, the Higgs boson is a feature of the Higgs field, which fills the whole universe. Like other quantum fields, it can be excited into making a particle, or it can be chill and relaxed down to its lowest state. But the Higgs boson, the Higgs particle, the excitation of the Higgs field, has all sorts of particle like properties. It moves, it has mass, and the value of its mass is really important. It's important theoretically, and it's important experimentally.

Absolutely. The big question is how do you measure the mass of something so important, so crucial to the concept of mass itself, like the Higgs boson, and so as usually you're wondering how many people out there had thought about this question and wonder if they can just ask the Higgs boson it's mass.

How rude, But thank you very much everybody who volunteers for this segment of the podcast. If you would like to participate, please don't be shy. Write to me to questions at Danielanjorge dot com. I am waiting for your email.

So think about it for a second. How do you think physicists measure the Higgs bosons mass? Here's what people had to say.

I know from the episode on where does the Higgs get its mass that you can look at how it interacts with the other fields like the top quark and the strange cork, and maybe with its interacting with its own field. But I have no idea how you measure it.

I now believe that we can view a boson, and so therefore I would imagine you could put it in a particle accelerator and throw something at it, and by that makes the calculations to measure its mass.

Measuring the mass of the Higgs is going to be exceedingly difficult. Even an optical system would probably be much too large to get the mass of the system. I one could assume that some interplanetary system telescope might actually be a way to go, if we were able to figure that out.

If I remember it right, the Higgs boson was discovered when they could detect a pair of photons that were emitted in the collider. So maybe its mass would be equivalent to the energy of those two falls.

I have no idea.

It could have something to do with its track after a collision analysis.

It's third, all right. I am with the last person here who said I have no idea. Sounds like a great title.

For a book. We should write a book like that.

Maybe title it we have no idea and make it available for purchase at bookstores and any kind of book website. That would be a good idea.

That would be a very good idea. In fact, if you went to we have No idea dot com, you might even be able to find such a book.

That's an amazing idea. But yeah, this is an interesting question. How do you measure the Higgs Boson's mass if the Higgs field is what gives things mass. It's a bit of a conundrum there. So when we start at the beginning at Daniel, what is the Higgs boson for people who don't.

Know, So, the Higgs boson is an idea that came out of the nineteen sixties when people were looking at the electromagnetic interaction, which is mediated by the photon, and the weak force, which is mediated by the Z and the W boson. So you had these two forces which seemed pretty different. The weak force is very weak and it has these three weird bosons that mediate it, and the electromagnetic force is very strong. It's the one that we know, you know, makes lightning and magnets and all sorts of stuff and binds together protons electrons into atoms and weaves those atoms together into molecules and basically makes the structure of everything around us. So it's felt like very different forces. But people had an idea that they might just click together into one larger idea, which they call the electroweak force.

Now, what do people know about the weak force or how do we discover it and what do we think it was for?

Well, the weak force was discovered several decades ago, and it was known to be involved in radioactive decay. So, for example, when a nucleus decays down to a lighter element, it does so using a process called beta decay. Then that involves the weak force. So we knew that the weak force was a thing, and we knew that it did some stuff and it was different from electromagnetism. We had postulated the idea that there might be a particle out there that only feels the weak force, the neutrino, but it hadn't yet been observed.

Mmm, Like, we knew about radioactive decay, like uranium decays into a lower mask uranium. But I guess you needed some kind of mechanism for it to do that, and you had to sort of invent the force to do that, or like it only made sense if you had this new kind of force.

Yeah, you can't explain radioactive decay using just electromagnetism or just a strong force. You need a new kind of phenomenon. And that's sort of the history of forces, right, we see all this stuff out there in the world, and we try to describe it using sort of like the shortest possible list of explanations. But sometimes you have to add one, you know, like when first time people ever saw lightning, they're like, hmm, well, you can't explain that with everything we know, so let's add some into the lists. Let's say there's a new kind of force electricity, and people saw magnets and they're like, ooh wow, this is a cool new thing. So so then magnets were added to the list. Later we try to shrink that list by seeing if we can combine those forces. So electricity and magnetism actually two sides of the same force, just one idea electromagnetism. So the weak force was responsible for a distinct kind of phenomena that we couldn't explain using other forces. But then people were eager to see if they could squeeze it together with the other forces.

What made them think that you could squeeze them together, Like, for example, they didn't try to squish together electromagnetism and gravity, did they?

Oh? Yes, they did. Einstein spent most of his life trying to accomplish that. Actually, and failing, and so theoris is basically trying to squeeze everything possible together.

You know.

It's like we're looking at a bunch of puzzle pieces on the table and we're like, hmm, does this fit with that? Nope? Does this fit with that? Nope? And electricity and magnetism almost fit together, just perfectly together with the weak force, like they clicked into place, almost perfectly. There was just like a little gap missing, and that gap was the Higgs boson.

Oh interesting, So the Higgs field and the Higgs boson was that missing piece exactly.

That's why they suspected that it existed, because it seemed very likely that these two forces could click together, but it didn't quite work. The problem was that photons have no mass lists right, but the W and Z bosons were very very massive, and that made it very very hard to click these two together unless you had some special thing out there which could give mass to the W and the Z and not give it to the photon. And that's what the Higgs does. It solves this problem of electroweak symmetry. It's called and know.

They try to bring in the strong force. They just decide to the strong force.

People basically work on every combination. If you could bring the strong force together with the electroweak force, then you've achieved a grand unified theory, something nobody has been able to make work so far.

Mathematically, would you have to call it like the electro met force. It's not weak, it's not strong, it's just kind of meant.

Well, you know, there'd be an interesting argument there about like which names get kept and which names get dropped. I don't know if you noticed, but when electromagnetism got merged with the weak force, magnetism got dropped, like the least influential partner in a law firm that merged with a bigger firm. Right, it's just gone.

They couldn't just keep phyphonating.

I guess, I don't know. I think they could have the bummer to lose magnetism. I like magnets. I don't know what they would call it. But the official name right now is the grand unified theory. You can bring those together, then you have a grand unified theory. And people have been trying all sorts of ways, but nobody's been able to make it click.

All right, So then the Higgs boson and the Higgs field made the electromagnetic force and the weak force click together. So that's kind of where it came from, the idea where it came.

From, right, that's right, That's why we thought it had to be there. It or something else which did that job, which gave mass to the w z bosons. And also they were able to add a little piece to the Higgs force and say, oh, also it interacts with all the matter particles and gives them mass as well. So it's a very cute little idea. And then we found it in twenty twelve, this fantastic triumph of theoretical physics, to say, you know, there's a pattern out there that's missing a piece. It would make much more sense if it existed in the universe, and boom, there it does. It makes you feel like, wow, math is not just like describing the universe. Maybe it's dictating how the universe works.

You know, wait, which math the math or one of the.

Math the math? And in this case it's group theory, this really weird, abstract kind of math that was invented by a bunch of French guys in the eighteen hundreds, not because they were interested in particle physics or really physics at all. They were just like, huh, look at these cool symmetries and patterns, Maybe we can describe them mathematically. And then decades later particle physicists were like, ooh, that math perfectly described the patterns we're seeing among these particles. Thank you very much mathematicians for inventing this tool.

All right, So, then the Higgs field and the Higgs boson is what gives other particles their mass, right, Like, if the electron has a certain mass, meaning that it's hard to get it moving and it's hard to get it to stop, that's inertial mass. That's all due to the Higgs field.

That's right. As the electron moves through the universe, it interacts with the Higgs field that changes how the electron moves in a way that to us looks like the electron itself has mass. And there's an argument to be made to say that the true, the real, the pure electron has no mass. But what we see isn't the pure electron. We see this like class out of an electron interacting with Higgs bosons, and that's what we call an electron because that's what we interact with. We see, we measure in our laboratory, and that object the sort of electron interwoven with the Higgs field. That thing has the mass of an electron.

And that's also how you explain how some particles like the photon don't have mass. Right. You just figure out that in the universe, some particles interact with the Higgs fields and then some don't, right, like the photon doesn't interact with the Higg fields, and so it doesn't have this inertial mass.

Right exactly. And on one hand, it answers a deep question why does the electron have mass? The answer is, oh, it interacts with the Higgs field, But it doesn't answer a much deeper question, which is like, well, why does the muon have more mass? The answer is just, well, it interacts more with the Higgs boson, sort of like kicks the question down the road to like, well, why does the muon interact with the Higgs boson more than the electron? We don't know. That's just like a number out there.

We have to measures, like, you didn't really answer the question, you just changed the name of the thing.

Well, we answered the question, but it revealed another deeper question. It's like we ran the ball down the field another ten yards somid some progress. We know a little bit more how to focus. But no, we definitely didn't finally answer the question.

And so the Higgs field gives mass to other particles, right, like quarks and electrons and its cousins. Even the neutrina is a little bit of mass, they think, right.

The neutrinos definitely do have a little bit of mass. We don't know exactly how much they have, but we know it's very very small. We don't actually know that neutrinos get their mass from the Higgs. That's one idea that there are neutrinos and anti neutrinos and they do the same thing the other particles do and get mass. It's also possible the neutrino is even weirder. It might be its own anti particle, and so it might get its mass in another way. Remember, the Higgs boson is not the only way to get mass. You can get mass anytime you have any kind of internal stored energy. For example, we think dark matter probably doesn't get its mass from the Higgs field. So neutrinos might do the same things electrons, or they might do something totally different.

M interesting. All right, Well that's the Higgs boson and we know it gives other particles mass. But the question now is who gives the Higgs bulls and its mass and more importantly, for this episode, how do we measure it? And so let's dig into those questions. But first let's take a quick break.

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All right, we're talking about the Higgs boson. Would you say the world's third most famous particle?

Third most famous? That might be the most famous. I think it's Michael Jordan of particles.

Really, you think it's more famous than the electron quarks maybe, or photons. Photons are really probably up there. So I would say it's like photons, electrons, and then maybe the Higgs boson.

I guess I probably have a skewed view of it, but I would guess Higgs boson first, and then electron.

I guess it is the most popular particle among physicists who study the Higgs boson. That makes sense.

I would say, I have a massive interest in the Higgs boson.

Yes, you're heavily biased. All right, Well, we were talking about how the Higgs field and the Higgs boson gives mass to other particles, but then now the question is what gives Higgs boson its mass and how do we measure it?

Yeah, the Higgs boson is like the barber who shaves himself for herself. The Higgs actually gives mass to itself. Right. The Higgs is a really interesting particle because it interacts with itself. That's not true for every particle, like the photon, for example, only interacts with particles that have any electric charge plus or minus a neutral particle. The photon will just fly right by, and the photon is neutral electrically, so it doesn't interact with itself. But the Higgs boson does. Interact with itself. Two Higgs bosons coming near each other will bounce off each other or attract each other sometimes.

WHOA Okay, So I guess that is kind of strange and different. So the Higgs boson when it's out there and it sees another Higgs boson, they can ignore each other.

They cannot ignore each other exactly. They're like x's that are still angry at each other. They always end up entangled.

Are you saying the whole universe is one big, uh, sad and dramatic story.

Yeah, And then they go home. They both eat chocolate to feel better. Now, the Higgs boson flies through the universe, and like other particles, it feels the Higgs field, and it interacts with the other Higgs bosons, the other manifestations of the Higgs field and pigs up mass. And so the interaction of the Higgs field with itself gives it mass.

Is that the order you would put it in, Like you have a Higgs boson, which is like a little blip in the field, and then that flip interacts with the field it's made out.

Of, too, exactly in just the same way that an electron interacts or the Higgs field. A Higgs boson also interacts or the Higgs field, and it has a similar effect on the Higgs boson as it does on the electron. What we're measuring when we measure the Higgs boson is actually this little cloud of a Higgs interacting with other higgses.

So then that means if the Higgs boson has inertial mass, that means the Higgs boson is not doesn't go at the speed of light.

The Higgs boson does not travel at the speed of light exactly because nothing that has mass can go at the speed of light. And the Higgs boson mass is sort of interesting from like a philosophical perspective, like whoa the thing that has mass gives mass itself. It's like Santa Claus giving himself a present or something. But it's also really fascinating theoretically for other reasons because the Higgs boson doesn't just get mass from its interactions with itself. It also gets mass from its interactions with other particles. Like we know that the Higgs interacts with electrons, and we know that interacts with top quarks, and those interactions give mass to electrons and top quarks, but also to the Higgs. So the Higgs gets its mass from interacting with itself and from interacting with the other particles.

Wait, so the mass of the Higgs changes depending on who's around it. Like, what if there's no electron or meal on around it, would that mean the Higgs boson is lighter?

Question because I said fields, and those fields are everywhere, or there's always an electron field and there's always a top quark field. So the Higgs boson interacts with those fields, whether or not they are actually electrons or top quarks around, whether those fields are excited enough to make real particles, it interacts with the fields themselves.

Well, I guess, just for the record, I think it's okay. Santa Claus wants to buy himself a gift. I mean, the poor guy, I mean, allwise he only gets one birthday present a year from Missus Santa. He can buy himself a little some fum.

Yeah, go ahead, Santa Claus, get yourself some dark chocolate.

That's right, you do you? Although maybe he likes white chocolate.

Yeah, maybe he likes peppermint bark. Who knows, somebody's got to like that stuff they keep making it.

Maybe it's the Santa himself.

But there's something of a mystery about the Higgs boson mass, which is why we're so interested in measuring it, and that comes from its interactions with these other particles. It's interactions with matter particles like electrons and top quarks that makes its mass much much bigger, and when it interacts with other bosons like w bosons or gluons or whatever, that makes its mass smaller. And the fascinating thing is that these two numbers are really really big. They're like billions of times bigger than the eventual mass of the Higgs boson, which means these two numbers sort of cancel each other out almost exactly. It's kind of a mystery of modern physics.

Mm weird. So the Higgs field is that the only field that interacts with all the other fields, or do all fields interact with each other? Or is that unique to the Higgs field. It seems like maybe the Higgs field is in it's just in everyone's business.

Every particle we discovered so far feels the weak force, so the Higgs feels the weak four where it's just like the neutrinos do, and the W and the C and the quarks everybody feels the weak force, but the Higgs is neutral, so it doesn't interact with photons directly, for example. But it's fascinating to me that you do this accounting. Like the Higgs boson gets a little bit of mass from interacting with itself, we don't know exactly how much. Then it gets a huge amount of mass from interacting with electrons and nuances and stuff, and then it loses a huge amount of mass from interacting with ws and zs, et cetera, and that comes back to almost zero. Like these two big numbers, the huge addition and the huge subtraction, don't have to be close to each other. They're two enormous numbers, and yet they almost balance brings the Higgs boson mass back down to a reasonable value. In another universe, the Higgs boson could have been like a million times heavier than it ended up being so heavy we could never even discover it.

H I guess that's a weird concept for a non particle to understand, which is like, how do you lose mass in an interaction? What does it mean that, like the Higgs boson loses mass when it interacts with certain particles, like it gets lighter and moves faster. It's easier to move around. What does that mean?

I think intuitively, the way to think about it is that interacting with some of these fields adds to the internal stored energy of the effective Higgs boson, and interacting with other fields decreases the internal stored energy. Adding to the internal stored energy means getting more mass. Losing internal stored energy means decreasing your mass. So it's not like it gets a kick. It actually like sucks away some of the internal stored energy the interaction with some of these fields.

But then that's a whole different mechanism for getting mass, right, which is like having stored energy inside that doesn't come from the Higgs field, does it?

In this case, it comes from the interaction between the Higgs field and these other particles. So even the Higgs field interaction you can think about as internal stored energy. Like you think about the electron moving through the universe, what is its mass? You could just say it comes from the Higgs field, but really what's happening is you're creating a new object, which is this electron that interacts with the Higgs field, and that thing has energy which in the end is coming from the Higgs field, and it's storing that energy internally in this new thing, this like cloud of electrons and Higgs is sort of interacting together. So it's really all the same kind of mechanism. The Higgs is like an example of how you can have internal stored energy, but you're right, it's not the only one. Like other forces can give you internal stored energy, like the gluons inside the proton give you internal stored energy.

And then when those get a lot of internal stored energy like in the proton, it feels heavier. Is that also due to the Higgs field or is that just due to some other unknown mechanism in the universe.

That's just the fundamental nature of mass that we don't really understand. That internal stored energy has inertia. And you know, you can change the relationship between those gluons increasing or decreasing mass, right, So if those gluons interact with something else outside and change their relative energy levels, that can change the mass of the particle.

Well, I guess the other question I had was, you know, you said that the Higgs boson doesn't move at the speed of light, but at the same time it's a part of that gives other particles mass. Does that mean that mass is not instantaneous or that there's some kind of delay in how the universe or how you feel mass in some particles.

Like if you change the mass of a particle, would that ripple out at less than the speed of light?

Or like if an electron moves, you know, the inertia you would feel is somehow delayed because it has to get it from the Higgs field, which doesn't move at the speed of light.

Information about any motion is always delayed, even if it travels at the speed of light. Right, Even like gravitational waves, which travel at the speed of light, are not instantaneous. So whether or not you travel at the speed of light or not, you're still not propagating information instantaneously.

So I guess I mean more of a delay, like you could see something happen before you feel its mass.

I think we had to pull apart a little bit here the gravitational and the inertial situation, because to see something's mass really means to observe it moving. Right, Mass is all about like what is your inertia? How do you move through the universe? How do you respond to forces? And we're not talking about like how your existence changes, like the curvature of space time and ripples from your acceleration. Right, we're not talking about gravitational waves. We're just talking about inertial mass.

Well, I guess that the question is the same. You know, do you feel inertial mass at a later time that you would like if a photon bounced off of an electron.

It's a great question. I haven't thought about it before, but I think that probably what's going on is that this is all internal to the object we call the electron, and we don't have enough energy to like break the electron open and see the Higgs is inside propagating. We just like wrap that whole thing up into an object we called the electron. And what we're talking about here is something that's really going on inside the electron. You'd be worried about, like how long it takes a Higgs boson to move from one side of the electron to the other. But from our point of view on the outside, the electron is effectively a point particle, so it's not really an issue like whether the Higgs can get from one side of the electron to the other to make it like a consistent object with a single kind of mass.

It just seems like it's it's like a full that has a certain delay to it, you know, like a slower force than say the ectro magnetic force, which communicates with photons, which are going at the speed of light.

Yeah, that's right. Photons do travel at speed of light, and ripples in the Higgs field travels slower. There are some particles whose mass changes. Remember, neutrinos don't have a definite mass when they are created. They are a mixture of various mass states, so that kind of inertial mass information might propagate it less than the speed of light.

All right, Well, let's get to the main question of the episode, which is how do you measure the mass of the Higgs boson? That was kind of a part of what the big discovery was in twenty twelve, right, Like you kind of had to guess what its mass was to know where to look for it.

Yeah. It's a really interesting bit of scientific history because when Higgs came up with this idea, his theory worked no matter what the mass to the Higgs was, Like, the Higgs could be very very low mass or super duper honk and heavy and his theory would still work. That's cool. It makes a very powerful theory, but it's also sort of frustrating from an experimental point of view because he didn't predict the Higgs mass. If his theory only worked for one value of the Higgs mass, then he could have said, go out there, look for it. It has this value, I predict it, you know, like baby Ruth calling his shot. But instead he said, well, it might exist and it might have any value. So you got to look for in all sorts of different ways.

Meaning like the mass would work no matter what the mass of the Higgs boson is, or would you have like very different universes if it did have different masses.

If you know all the particles that are out there in the universe interacting with the Higgs boson, then you know what its mass is, because its mass comes from interacting with itself and interacting with all those other particles. If you don't know the other particles out there in the universe, you don't know everything that's contributing to the Higgs mass. And so we didn't know. We didn't know what all the particles where We still don't know what all the particles are if you measure all the other particles very very precisely, then you can predict what the Higgs mass could be. But that's only if you know all the particles in the universe, and we're pretty sure we don't.

So I guess he just didn't know what the mass of the Higgs boson was supposed to be, just because you didn't have all the information about what else is out there in the universe exactly.

And that's another reason why knowing the mass is exciting, because it gives you a way to tell, like, is there something out there we don't know about, something else interacting with the Higgs field and making it heavier or making it lighter. What we can do is predict the value the Higgs field based on all the particles that we do think are out there, and then we can go out there and measure the Higgs and say does it agree with our prediction?

All right? So then we discovered the Higgs boson, and so what is its mass? And how do we know what its mass was?

So we measure the mass of particles in a weird unit. It's called the GeV giggle electron volts one billion electronvolts. It's actually a pretty convenient unit, because the proton weighs about one GeV. Our electrons are much much lighter than that. For example, they're like half of an MeV half of a million electron volts, and the Higgs boson is about one hundred and twenty five of these things. So one hundred and twenty five point three five plus or minus point one five GeV.

The mass of the Higgs boson is one hundred and twenty five times greater than the mass of a proton.

Yeah, exactly. It's the second heaviest particle we know. It's lighter only than the top quark, which is about one hundred and seventy three GeV.

Well, it's kind of weird to think about, right, Like the electron is thousands of times lighter, and yet when it interacts with the higgs boson, the higgs boson is heavier.

Yeah, exactly. The top quark interacts with the Higgs boson like crazy. Those two guys have a party every time they meet, and that's why the top quark is super duper heavy.

That's why it's the top because it's it's a fun particle. It's the finest. I don't know it likes to party.

But we know the Higgs boson mass very very precisely. We know it more precisely than the top quark, even the topqrk we discovered in the nineties and we've been working to measure its mass ever since then. The Higgs boson, we know a precision of one part in one.

Thousand, all right, So then how do we know the mass? How do you measure the mass of any particle. You can't just put it on scale, right, and you can't just like drop it from a building to see how fast it accelerates exactly.

We can't do any of those kinds of things that you usually do because these particles last for only a few moments. You know, we're talking like ten to the negative twenty three seconds, which means it technically we don't even see these particles. Nobody's ever seen a Higgs boson. They never even seen a track a Higgs boson left in one of our detectors, because they just don't last for long enough already, and then it decays into other stuff. We know the Higgs exists because of patterns in those particle decays that are consistent with the Higgs being there, and inconsistent with the Higgs not being there, So then to measure its mass, we have to look at the patterns of those particles and try to extract that information the streak that those particles left after the Higgs boson turned into them. M.

Yeah. We often use the analogy of like studying an accident scene. After the accident, you sort of study the debris and you kind of figure out like, oh, this car crash into that car is here at this point, and they crashing in the back corner, and because the fenders over here, we know how fast they were going. You're saying, like, somewhere between the crash and finding the debris, like a Higgs boson popped up into the universe and then it disappeared again.

Yeah, And the car crash analogy is helpful, but it's also misleading an important way, because when you're looking at a car crash, you're looking at pieces of the car, right, the fender is here and the windshield wipers over there. When you're looking at the results of a particle collision, you're not looking at like pieces of the Higgs boson. The Higgs boson doesn't like break in half, and you find bits of it here and bits of it there. It converts from a Higgs boson into totally different kinds of matter. So, for example, a Higgs boson can decay into two bottom quarks, and that doesn't mean that there are two bottom quarks inside a Higgs boson. It means that the energy that used to be in a Higgs field is now in the bottom quark field. The Higgs is gone. It's not like it's bits are rearranged into something else. It's gone, and that energy is now in a different field.

Right, Yeah, things trend into energy, but sort of the analogy is still the same, right, Like all the parts still have to fit together at the end, Like you can't just invent energy out of nowhere, Like you have to do some accounting to make sure that all the bits that you got at the end were part of the same thing at the beginning. And that is actually how you find the mass, right Like you do the through accounting.

Exactly, through accounting basically of quantum information and energy. Quantum information is sort of amazing. We talked about the podcast a few times, and the idea is that quantum information is not destroyed in the universe, which means that every past moment in the universe creates a unique present because as a unique connection, as where there was a one to one mapping, you can reverse it. You can say, I'm going to take the present, I'm going to rewind it figure out what was going on in the past. And so you can take the particles that the Higgs boson decayed into, maybe like two bottom quarks that we see in our detector. You can figure out what the Higgs boson was doing. Most specifically, you can figure out its momentum and you can figure out its energy, and from those two pieces of information you can measure its mass.

I guess. So that means you sort of infer its mass, right, or you deduce its mass from what it's doing, or what do you see its progeny doing.

Yeah, and that makes it sound a little bit indirect, and the end all measurements are indirect, are all inferences based on observation. That's when we feel pretty confident in But yeah, we're measuring the energy of the two particles. And you know, one of the listeners actually came very close to answering it. He said the Higgs was discovered when they saw a pair of photons and maybe the mass is equivalent to the energy of those photons, and that's almost exactly right. The energy of those photons tells you a lot, and also their direction and their momentum tells you the momentum of the Higgs, and with that information together you can get the mass. Because remember the energy we're talking about like energy of motion, which is the momentum, and then energy of mass. And so if you have the total energy and you know the momentum, the last little bit has to be the mass.

Sounds like that listener was very.

Enlightened, brilliant, brilliant comment.

And so let's shed more light into this measurement of the Higgs bosons mass. What's hard about that and what what does it mean about our picture of the universe. So that's stick in to that, But first let's take another quick break.

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All right, we're talking about the Higgs Bosons. Higgs Boson researchers favorite particle.

Yeah, that's right, or maybe the most famous particle and maybe our favorite particle because it's the last one we discovered, and it's not very often that you discover a new particle on the top Quark in the nineties and the Higgs Boson in the early twenty tens and nothing ever since. So you spent a lot of time studying each one because they're precious.

So if you discover a new particle, that'll be your new favorite. I see how fickle your physicists are.

That's right. The young one is always the baby particle of the family, and you know you gotta love the baby.

It's falling the latest trend, the latest hid particle. Well, we're asking the question of how you measure the mass of the Higgs boson, and it seems like you do it at the Large Hadron Collider and any collise Can any collider study the mass of the Higgs? Or right now, is the Large Hadron Collider the only collider that can do that?

Well, the LAFC doesn't have a monopoly on it per se. It's just that it's the only one that has enough energy to make the Higgs boson, and so it's the only place that it can be studied. So far, we're working on plans for other colliders, including maybe even a Muan collider that can make like huge numbers of Higgs bosons. But you have to make it in order to study it.

And so we were talking about how you collide things and then you look at the debris and then you figure out that in some crashes like the evidence you see can only be explained by the Higgs boson, and from the debris can also sort of infer what its masses. And so we got that down pretty good.

We have that down pretty good. There's been a lot of really really careful studies, and this is not an easy thing to do. I mean, we're saying the Higgs boson turns into two photons or two bottom quarks or sometimes two w bosons, and we're just saying, oh, you measure those particles masses and energies. But that's not trivial. You know. That involves building and calibrating complicated detectors in order to measure those streaks and extract that information.

Yeah, and also like that, it doesn't happen every time you crash some particles, right, Like you have to collide trillions of particles to sort of get one where maybe a Higgs boson can be seen.

Oh yeah, great point. The Higgs boson is really really rare. That's why we collide particles so often, millions and millions of times per second, hoping that maybe like one of those collisions will give us a Higgs boson. So first we have to smash it up particles together to get a sample that's going to have a bunch of Higgs bosons in them. Then we have to try to isolate the collisions, and we think probably come from the Higgs boson, but that's not totally possible. Some of those collisions will always be due to other stuff that just happens to also give two photons that look kind of like a Higgs boson, or give two w bosons that look kind of like a Higgs photon. So you can never say this collision has a Higgs in it or that collision has a Higgs in it. It's always statistical. You have a set of collisions you say, we think there's like ten percent Higgs in here, or there's four teen percent Higgs in here.

But I guess since the Higgs boson gives all particles their mass, isn't technically the Higgs boson in all collisions too.

It is, but sort of in a virtual sense, like the Higgs field is everywhere, and the Higgs field is involved in everything, even low energy collisions. But if you want to study its mass, you have to make a real Higgs boson. You have to excite the field enough so that it pops out an actual Higgs boson, a real one, not a virtual one.

What's the difference.

Virtual particles really just saying another ripple in the fields, like information wiggling through the field. But that information can propagate in all sorts of ways that particles don't propagate. You know, particles, for example, have a specific mass, or real Higgs boson moving through the Higgs field has a very specific mass. Virtual particles don't have to follow those rules. They can have all sorts of weird masses, including like zero or negative masses. Virtual particles are not really particles, They're just ripples in the Higgs field. You can sometimes kind of describe using particle like words.

But I guess if the Higgs boson is so rare, really what's giving mass to the other particles then, because I feel like you're saying it's rare and virtual and you rarely ever see it, but at the same time, it's affecting us all the time everywhere.

Yeah, because the Higgs field is everywhere, even if there are no real Higgs bosons around, The Higgs field fills the whole universe, and it's constantly interacting with your electrons and your top quarks, so maybe what you're getting at is it is possible to detect the Higgs field and to deduce things about it from its interactions with those particles, right like, by measuring the top quark very precisely and measuring the w boson very very precisely, we can learn a lot about the Higgs field, and that's how they make those predictions of what the Higgs mass sort of has to be like. Before we found the Higgs Boson mass, we had ideas for what its mass might be based on these sort of indirect measurements observations of how it's affecting the other particles.

All right, well, let's get to what we know about the mass of the Higgs field. So you said, we know that it's one hundred and twenty five zero point thirty five GEVs plus or minus zero point one percent. What does that mean? Is that more than what we expected? It seems like it's a lot, because it's one hundred times more than the mass of the proton. But is that surprising or is that expected? Is it interesting that it weighs that much or could it have been any other mass?

Well, first of all, it's very impressive that it's measured so precisely. Like this is really hard. I guess it's kind of my job, so this horn, but like this is not my work.

Yes, according to people who had to do it, it.

Is really hard, you know, like a higgs boson decays the two photons. You got to measure those photons really precisely. You got to come up with all sorts of clever ways to know, like how can you tell the difference between photon and dis energy and that energy, and how do you know for sure? Like people spend weeks and weeks sweating over the details, the tiny little problems it might crop up in your photon calibration, which gets propagated to your Higgs boson calibration. And it's all because this number means a lot, as you were saying earlier, like the higgs boson could have been heavier, it could have been lighter. It was a little bit of a surprise to some people that it was so light, because remember, those two numbers have to somehow balance each other out, like a huge, big random positive number and a huge big random negative number somehow almost cancel out to give this slightly positive number. And there's some folks out there who were thinking that those numbers are never going to cancel out, that they're going to give us a huge number, like something so big we would never see it in the large Hadron colliner.

So it was lighter than people expected. They thought it was going to be even more huge.

Yeah, some people thought it was going to be really huge. Other people have ideas to explain that sort of apparent coincidence. They say, well, maybe there's a connection between all the particles that are making the Higgs heavier and all the particles that are making the Higgs lighter. Maybe there's like a balance in the universe, a symmetry that says, for every particle that's making the Higgs heavier, there has to be one making the Higgs lighter, and that's why these two things cancel each other out. Maybe there are a whole bunch of other particles out there and then just sort of like magically balancing everything that we have seen. And that's a theory called supersymmetry. It says to make those two different contribution's balance and keep the Higgs field very very light. So for some people, when we saw the Higgs boson mass was you think it's kind of heavy. Some people think it's kind of light. Actually, they thought, maybe this is a hint that there are these supersymmetric fields out there.

Could the Higgs boson have had zero mass? Was that a possibility when you went into it, or did the Peter Higgs theory say it had to have some mass.

It could have had zero mass, that is a possibility, But you know, then it would have been pretty easy to find because it would have been very easy to create, and early searches for the Higgs bosons in the seventies, for example, ruled that out pretty quickly. So by the time we turned on the Large Hadron Collider, we already knew the Higgs boson had to be heavier than like one hundred and fifteen or so gv, because remember, there was another collider in the nineties which ran into the early two thousands called the LP Large Electron Positron Collider, and that one would have found the Higgs boson if it was up to about one hundred and fourteen GeV.

All right, well, then what does it mean that it has a mass that it has? What does it mean for the future, I guess or our understanding of the models of the universe.

Right now, it means that there's no specific evidence for other particles out there. Like if the Higgs boson had had some very crazy heavy mass, it would mean, oh, it's getting influenced by another particle out there that's making it heavier, a particle we haven't seen yet. So in that way, like making a very precise measurement at the Higgs boson mass is a great way to test our understanding because these things are all connected. You might remember that there was a very precise measurement at the W boson mass last year. They gave a very weird result, a result that didn't agree with all of our calculations. And these are all tightly coupled. The W the top the Higgs. If you change one of them, it changes all the other ones. So getting a weird value for the W mass means maybe there's something else going on out there. So that's why it's important to get a very precise measurement. It's like without creating those new particles, you can be sensitive to their existence, which is a pretty cool way to explore the universe indirectly. It's also relevant to the question of whether the Higgs field is stable. How the Higgs interacts with itself changes how stable the Higgs field is, and that's connected to the Higgs mass. But the Higgs boson also, because it couples to itself, its mass effects whether might collapse. And if the Higgs field collapses, it changes the whole structure of the universe and our whole experience. So measuring the Higgs boson mass tells us whether or not the Higgs field is likely to be stable or unstable.

Mm you say that it also tells you whether there are more particles out there. So if you have this measurement down pretty good, does that mean that you don't think there are other particles out there yet to discover? You think we've maybe discovered them all.

Well, if you ignor where this recent measurement of the W mass by CDF, the one that says that everything is out of whack and the things don't agree, then everything agrees pretty nicely. The top, the W and the Higgs are all consistent with each other, and that means that there isn't evidence for anything new out there yet. On the other hand, it leaves this question unanswered of why the top of the W and all that stuff add up to give a Higgs that's so light. Like I said, just a coincidence. The masses of these particles are tuned to one part in ten to the ten, so that the Higgs boson just happens to come out to be this very small number. It seems like too big a coincidence, and so we're looking for another explanation. And another explanation might be other particles out there that like help balance the Higgs boson mass, but we just don't know so far.

All right, Well, I guess stay tuned. You have the large Heron collider. You just upgraded it, right, you're running that maybe faster than it had been before.

Yeah, that's right. We're getting more and more collisions every time, and more protons in every collision, and we're going to run it for another ten issue, and we're going to run it for decades longer and collect huge piles of events and sift through them for evidence to see if the Higgs is doing something weird. Because we can measure the Higgs boson mass in all sorts of different ways when it decased to photons, or when it decaysed to bottom quarks or in the case to w bosons, and we can also compare those against each other, like does the Higgs look heavier when it turns into a photon or when it turns into quarks or when it turns into w's. If there's any disagreement there, that's another hint that something new is going on.

The mask can change.

The mass should be the same, no matter how you measure it. It should be the same if it turns into photons, if it turns into bees orf, it turns into w's. But if there's something else going on, if it's not the Higgs that we thought it was, or if there's more than one Higgs, or if there are other particles getting involved, then you might measure different masses in those different decay modes, and that would be a signed this something else going on you don't understand.

Could be that the higgs boson is actually made out of white chocolate, not dark choker.

It's been Santus present to himself all this time, all this time.

That's right, it's the clouds ypothesis. Should have been the clouds field and the clawson. There you go, the santon. All right, Well, a lot of interesting questions talking about and thinking about in this fundamental particle of the universe. I guess the next time you step on a scale, think about how you're measuring what your mass is, and think about how many virtual or real Higgs Bosons are flying all around you and inside.

Of you, and how this is just one step in our unders standing of the universe. We have this crazy model we put together on our heads, and it makes predictions and it has blank spaces in it. Then we go out and confront the actual universe and see if we can get this model to describe everything that we experience.

So thanks for joining us, see you next time.

Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, concern natural resources, and drive down greenhouse gas emissions. House US dairy tackling greenhouse gases, many farms use anaerobic digesters to turn the methane from manure into renewable energy that can power farms, towns, and electric cars. Visit you as Dairy dot COM's Last sustainability to learn more.

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Daniel and Jorge Explain the Universe

A fun-filled discussion of the big, mind-blowing, unanswered questions about the Universe. In each e 
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