It’s time for a news update. This time from the field of particle physics. It turns out there have been all kinds of new and interesting particles discovered by the Large Hadron Collider and others. Let’s get an update from Pamela.
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Large Hadron Collider
CERN (European Organization for Nuclear Research)
Quarks = Up, Down, Top, Bottom, Charm, Strange
Elemental Particles =Fermions (quarks, anti-quarks, leptons, anti-leptons), and bosons (gauge and scalar [Higgs])
Tetraquarks and pentaquarks
Podcast Transcription provided by GMR Transcription
Fraser: Astronomy Cast, Episode 486: Particle Physics Update. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. With me is Dr. Pamela Gay, the Director of Technology and Citizen Science at the Astronomical Society of the Pacific and the Director of CosmoQuest. Hey, Pamela, how you doing?
Pamela: I’m doing well, Fraser. How are you doing?
Fraser: You’re back from all kinds of trips.
Pamela: I am. I most recently returned from attending a Communicating Astronomy with the Public meeting over in Japan where I got to be face-to-face with Avivah Yamani who’s our project director for 365 Days of Astronomy, so that was quite exciting. And all the other awesome humans who are in science communications from all the places I don’t get to visit were there, so it was amazing.
Fraser: Yeah, there was clearly this gigantic group that was there because my normal people for reaching out for outreach, each person was like, “Oh, I can’t this week. I’m in Japan,” “Oh, I can’t this week. I’m in Japan.” Like, okay, I get it now. I should be in Japan.
Pamela: Just ask. We can see if we can get you there next time.
Fraser: Alright, next year. I believe I communicate astronomy to the public.
Pamela: You do.
Fraser: Alright, let’s get on with this week’s show. So, it’s time for a news update, this time from the field of particle physics. Turns out there have been all kinds of new and interesting particles discovered by the Large Hadron Collider and others. Let’s get an update from Pamela.
Pamela: I want to start this episode with a disclaimer that I am sure there is a particle out there –
Fraser: That you missed?
Pamela: Yeah. I’m quite certain of that. So, this is going to be my best attempt, and I’m sure there’s going to be gaps, so apologies if I miss your favorite new discovery. I’m doing the best I can.
Fraser: And also that you are not a particle physicist –
Fraser: – so it’s entirely possible that you’re going to get the obscure, interesting things about these particles perhaps a little off.
Pamela: That is true as well.
Fraser: But you make up for it with raw enthusiasm.
Pamela: Yes. I went down the most amazing rabbit hole preparing for this particular episode, and it was quite cool because there is a lot going on.
Fraser: The funny thing, I was having a conversation with Paul Sutter about the Large Hadron Collider, and he said that one of the things that’s kind of funny about it was it sort of has turned up almost the most disappointing result possible, which is that it did its job but no more.
Pamela: That’s true.
Fraser: Yeah, right? That it was built to discover if the Higgs particle is a thing –
Pamela: Which it is.
Fraser: It did, Standard Model confirmed, and then has been desperately trying to go further to figure out whether supersymmetry’s a thing, trying to find which flavor of the Standard Model is correct – anything. Can we get a hint please? And so far, it has not turned up. But it has turned up a lot of other really interesting particles that fit nicely still within the Standard Model, so I thought it was really funny. He was sad that all that the Large Hadron Collider had done was done its job, and done it well, and confirmed the theories but not given all those “that’s unusual” discoveries.
Pamela: I think what you just described is actually very well summed up by a CBC news report that is titled “New subatomic particles predicted by Canadians found at CERN”. It’s poorly punctuated. The Canadians were not the ones found at CERN; it was the subatomic particles. But moving on, there is a pair of Canadian particle physicists Randy Lewis and –
Fraser: Found at CERN.
Pamela: – and Richard Woloshyn, and the two of them had done a number of predictions based on if you look at quarks, and you rearrange the quarks, and you look at how the quarks can meet with the other quarks, and how all of the forces work, you should be able to get all of these heavier, unstable particles as you force the Large Hadron Collider to higher and higher energies. And there were indeed some of these subatomic particles discovered, and the quote they have in the article is, “Lewis said he saw the paper when it was first published online at 8:00 p.m.”
And he responded, “I saw the title and thought, ‘Oh, I predicted those – I wonder how it turned out?’ he recalled. ‘I looked up the numbers and said, “Yeah, that looks a lot like what I predicted – great.”’” I’m like, you predicted particles, they got discovered, and it’s gotten so blasé that people are like, “Cool. It matched what I predicted. We’re good.” And they move on with life.
Fraser: Yeah, so what is the particle that had been predicted and then found?
Pamela: This is where I have to say we shouldn’t be allowed to name things; it’s the Xi_b’ and the Xi_b*.
Fraser: You’re gonna have to explain some of these. Does it matter? Do we know why the names have the names that they do? I mean, it’s like saying, “Why is the strange quark –?” you know.
Pamela: It’s part of how they predicted – you start combining quarks, and then here are the letters we’re going to assign to these combinations of quarks. So, in this case, we have a bottom quark and two down quarks to make one of these particles, and the other one is another combination with the bottom quark, and it’s this bottom quark that’s the issue because it weighs a lot. So, finding particles that include the bottom quark is something that’s new and exciting, and apparently Canadians don’t get very excited when you ask them for quotes in the newspaper.
Fraser: “Huh. I predicted this.” Okay, so just to give people just a tiny little bit of background information, when you mash quarks together –
Pamela: So, they’re not mashing quarks together. So, what the Large Hadron Collider does is it accelerates protons in the kind of experiment they were talking here. In other cases, it accelerates other ions, atoms. It accelerates streams of protons to extremely high velocities, smashes them together, and all of the mass energy of the protons and all of the kinetic energy of the protons get combined together in one very small volume. And this released energy from both the mass and the kinetic energy – and it’s the kinetic energy that matters the most here – is free to form new and interesting particles including quarks that have not yet decayed into more stable formats.
And so, in this case, we have all of these stable things that we’re used to dealing with are made of combinations of the up and down quark. This one, it went and included the bottom quark as well, making it unstable and making it harder to create, harder to observe. But they did it, much to the non-excitement of the predictors.
Fraser: Right. The question that I was asking though, right, is that, for example, a proton is made of some combination of up and down quarks mashed together into a particle.
Pamela: They’re not mashed; they’re bonded.
Fraser: Sure, bonded. So, that is how you get a proton, that if you put some combination of up and down quarks in a very close area, you’re gonna get a proton.
Fraser: And if you put a different combination of quarks, you’re gonna get a neutron.
Fraser: If you put a different combination of quarks, you’re gonna get – and those are the stable ones – and then you’ve got all these interesting things, all this other stuff. And so, I guess what you’re saying is you took quarks that normally aren’t seen together created particles with the Large Hadron Collider that decayed into the combinations of quarks that normally wouldn’t be seen together.
Pamela: Exactly. And the difference between these particles is just the spin of the particles, and so they’re made of the exact same constituent quarks, and cool, we got new particles. This was the first one I found back in 2014, so we went from Higgs to – well, nothing’s exciting anymore.
Fraser: Right. But if you look at – like on Wikipedia and stuff, you can see these big grids of all these particles, and it’s like this one is the up-up-down, and this one’s the – And so, they’re taking these different combinations, that’s where the prediction comes from is you say – like the period table of elements – there should be something if you put a charm, and an up, and a strange together, that should make a particle. It will probably have this cascade of particles when it gets released, it will probably have this kind of energy level that it’s gonna take to build it, and then when they run, they’re looking for that to happen.
And so, at this point, now that the basic framework has been done, you’ve got all these openings in the standard model, now it’s a matter of filling in all those blanks, right?
Pamela: And this is where the particle physicists on the theoretical side are two, not-exactly-excited Canadians in this story.
Fraser: You just keep hammering that, don’t you?
Pamela: I’m sorry. This is the funniest quote I have ever run across. These are two brilliant human beings who made a brilliant prediction and had the most non-exciting quote. So, here they are, working in their lab, working through the mathematics – and by lab, I mean probably an office with a computer – and they figure out what are the binding energies, what are the energies of the particles, and when all of this decays, what do we expect that spike in the power spectrum coming out of the Large Hadron Collider to look like. So, they predicted that energy that we would see in the Large Hadron Collider, and they got it right, and that was cool.
So, bottom-down-down, couple spin variations that have different masses – nailed it. And the frustrating part is this is just part of the normal, everyday Standard Model which we understand, we know how it works, but we don’t know why it works, and this drives particle physicists to extremes. And by extremes, I mean it drives them to create things like supersymmetry string theory, proliferations of particles, and we’re not finding any of these.
Fraser: Right, and that was back to sort of what I mentioned earlier on is still these deeper extensions to the Standard Model, I guess the best thing that they’re doing is able to rule out low-hanging fruit. They’re able to say, “Oh, the simplest parts are the parts of supersymmetry that we should be able to detect, we haven’t been able to detect, therefore that model of supersymmetry is probably wrong. But there’s a hundred more that you’ve gotta work your way through.
Pamela: And so far, we’re just on the straight and narrow of straight and boring Standard Model, which I don’t know why that delights me so much. I like the fact that our universe has potentially no deep underlying physics that explains why some of these things are true that we can understand at this moment.
Fraser: But if you went back 100 years and talked to Niels Bohr and said, “Hey, quarks. Here’s how it works. Here’s the Standard Model,” I think he’d be pretty interested. He’d be cool with it.
Pamela: Oh, yeah. And with the subatomic standard model, one of the paradigms, it’s not an accurate paradigm, but it’s the way my brain thinks about it is with the Standard Model, with particle physics where Kepler was with planetary dynamics, we know the rules, we understand the rules, we don’t know why the rules. And we needed Newton to get the why, and we just haven’t had someone come up with that right why for particle physics yet.
Fraser: So, a puzzle piece found. What else has come up out of the Large Hadron Collider?
Pamela: So, what’s cool is it turns out that quarks can partner up in more than just threes. For the longest time, we were used to our happy up-up-down, down-down-up, whatever all the normal combinations of three. And then in 2015, we found out that sometimes they come in groups of five – this is the pentaquarks. So, suddenly, we have this – it isn’t too suddenly. There was data from 2011 and 12 that hinted at this, but 2015 was when the confirmation came. And suddenly, there’s this entire new realm of ways that we can combine things, more math to be done, more energies to be predicted, and it’s just cool to see that nature still has surprises for us on how particles can partner up.
Fraser: Partnering particles. And so, it’s the same situation, though, right? A pentaquark, or five quarks together, dissolves pretty quickly.
Fraser: So, it’s not a stable thing. But then does that open up this whole idea that you could then have different combinations of five times –
Fraser: Five to the power of five, right? That gives you a lot of combinations.
Pamela: Six. They’re in evens.
Fraser: Right. So, you have a ton of combinations for how you can have these quarks be together.
Pamela: Yes. It’s awesome.
Fraser: Right. But they play no role in our day-to-day human society.
Pamela: No, no. But they’re cool.
Fraser: Well, it’s just got such a great name though, pentaquark.
Fraser: I like it.
Pamela: And not to be outdone – so that was 2015, and 2016 decided, well, if you can have particles made of three quarks, and you can have particles made of five quarks, let’s go ahead and find those made of four quarks. And so, 2016 was when the tetraquark particles came to be a thing. And this is where things start to become extraordinarily hard to pronounce. Pentaquark is nice and friendly. Tetraquark just makes me struggle for some reason.
Fraser: Yeah, it doesn’t roll off the tongue as nicely. When I think about the way that people are searching up the periodic table of elements, they’re adding protons to atoms – they’re bombarding them with protons, and they are making, briefly, ever more heavier elements, and that’s one line to move down. And then I guess this other line is to say, “Let’s make individual particles that are made of more quarks.”
Fraser: And it’s kind of like – I don’t know, like when I think of from a computer science standpoint, let’s have a faster processor or let’s have a processor with more processors, right? And that’s the way computer science is going these days is let’s make a computer that has more cores as opposed to just a faster computer because it’s more productive.
Pamela: So, at least with going up the periodic table of atoms, they were just trying to deal with how do you hold it together before it decays into multiple particles. And the issue is the force across the diameter of the atomic core, so if you don’t look fast enough, the forest literally can’t reach all the way across that atomic core, so the atomic core falls apart. With the quarks, the entire thing is just like, “We don’t wanna do this, man.” And it becomes pure energy in a completely different identity. So, it’s not a nice, clean parent and daughter particle like you get with the periodic table of atoms, and some people refer to particles as the periodic table of particles, which is why I’m trying to be specific.
Here, they go back into pure energy, and can come back out in a whole variety of different ways just adding to the confusion. Anyways, we had 2015, pentaquarks – and I’m gonna actually throw in a dig. The pentaquark people were amusing and pointed out that their particle they were going to call Charmonium, which sounds like some sort of a Pokémon –
Fraser: Gotta catch them all.
Pamela: Yeah, it’s kind of adorable, but the tetraquark people a year later gave their particles the names X(4140), X(4274), X(4500), and X(4700).
Fraser: I mean, unless you’ve got some reason why that’s supposed to make sense, please continue.
Pamela: No, those are just the names that are related to their masses. They’re combination of charm and strange quarks in that particular case. There are also some Z versions of the tetraquarks, so, yeah; they don’t give these things exciting names.
Fraser: But I mean, we’re at the point now where stars don’t get exciting names, right? Stars just get great big numbers depending on their catalog, so I think this is a good thing that there are so many particles now that you just don’t even have to name them anymore.
Pamela: That’s fair. So, then, 2017 came along, and here, we continued to up the energies that the Large Hadron Collider collisions were occurring at up the energies of the masses that had the potential of being found. And they found yet another set of new particles. In this case, we went back to our standard – what we call Hadrons. These are particles that have three quarks. Here we have an Omega_C0 and a Xi_C that comes in a couple of different varieties. The Omega contained two strange and a charm.
The Xi particle contained a charm, a strange, and an up. And this was going back to that same model of just plugging through and figuring out what are all the possible combinations of three quarks, can we attain their energies, and if we look, do we find them. And we’re just pulling these out one at a time.
Fraser: Right, and I sort of imagine this, like a particle physicist, a theorist sits down and goes, “Huh, if I put two ups and a strange together, what will that probably look like? What will the amount of energy be that it’s gonna take to make that? What are the resulting cascades of particles that we should detect in the detector?” And then they tell the people who are actually operating the Large Hadron Collider, they say, “Crank the energy up to this exact number, and then give me the data from the detectors, and you should see this precise cascade of particles coming out. And if so, then Nobel Prize, please,” right?
Pamela: Not all of them are getting Nobel Prizes sadly.
Fraser: No, I know, at this point.
Pamela: I’m pretty sure our two Canadians with unexcited quotes aren’t anticipating a Nobel Prize.
Fraser: They’re sorry.
Pamela: They are. And they’re polite. So, we have our up-down-charm-strange-top-bottom quarks, and they can be added up in all these different ways, and it’s all politely predicted by the Standard Model, and so far, that’s the model we’re sticking with.
Fraser: Have you got anything that pushes, challenges, threatens the Standard Model?
Pamela: No. I do have something cool out of superconductivity though.
Pamela: So, it turns out that the Large Hadron Collider is not the only game in town when it comes to discovering new particles. This was something I’d never heard of before – I really enjoyed prepping for this show. It turns out there was a prediction by Ettore Majorana back in 1937 that you could have fundamental particles, fermions, that are both their own matter and their own antimatter version. So, if you switch over to the antimatter universe, nothing changes with this particular particle.
And having predicted in 1937, we have as of 2017 totally confirmed that this sucker exists. It’s started to have predictions on how to make the bound states and how you might be able to find them in superconductors in 2008. They started to see early signs that they were there in 2012. 2017, they are ready to say, “Here they are. We have a particle that is its own matter and antimatter pair.”
Fraser: Awesome. And predicted, it only took, what, 80 years to figure it out.
Pamela: The little things. It takes time sometimes.
Fraser: But does that prediction cause any problems to the Standard Model?
Fraser: No? Alright.
Pamela: We’re in a nice, beautifully predictable, handleable, no supersymmetry unpronounceable words, particles required, and I don’t know why I’m so overjoyed at this, but –
Fraser: I am surprised actually because I am always telling people that physicists, that scientists are delighted when things turn up that are unusual and unexpected, and I know dark energy tickled you.
Fraser: So, the fact that the Standard Model is just holding up, it’s gotta be enraging. How can you even hold it together?
Pamela: I think it’s a matter of the fact that there are so many people out there making up particles in order to come up with underlying physics that we have no evidence for. I don’t like that just at a purely emotional level because the Standard Model is based purely on observables, and I’d like to find a why that doesn’t require adding a gazillion things to the universe that have no observable evidence yet. It’s purely emotional. It’s not logical.
Fraser: Yeah, no kidding. Like the universe has any obligation –
Pamela: It has none.
Fraser: – to be simple and provide what you’ve acquired. No, ma’am. The universe has its own rules, and it’s our job to discover them as they are. You know this.
Pamela: I know this, but every time someone comes up with a theory and says, “And we can’t prove it currently,” or says, “And this requires creating all of these things that we have no evidence for,” part of me is like, “Okay. I’m going to wait until there’s evidence. My observational heart denies you until you have proof.” And my observational heart is overjoyed that currently, the universe is like, “Nope.”
Fraser: Sorry, theorists. Well, you know what it is? It’s your anti-string theory bias.
Pamela: It’s true. It’s true.
Fraser: Which has actually been now, I believe, most people have your anti-string theory bias, so I really like to feel like you were ahead of the curve on this one.
Pamela: I don’t know.
Fraser: You were hating string theory before hating string theory was cool.
Pamela: It’s true. It’s true.
Fraser: Did you have anything else?
Pamela: No. Just the fact that the Large Hadron Collider is –
Fraser: No, we get it. We get it.
Fraser: The Standard Model holds.
Fraser: The Large Hadron Collider was a disappointing success.
Pamela: No, it was a glorious success.
Fraser: A glorious success. It answered all of the questions, yeah. And didn’t ask any new ones, didn’t give us big, new confusing “that’s funny”. We’ll have to go back to the superconducting supercolliding one in Texas. The tunnels are still there.
Pamela: I thought they filled them in.
Fraser: They may have filled them in a bit, but no, for sure the tunnels are still there.
Fraser: Yeah, so go back to Texas. Well, before we wrap up this week’s show, I just wanna remind the people who are listening to this as a podcast that Pamela and I actually stick around for another half hour and answer everyone’s questions live in the chat, so it’s another half hour of us talking about news and anything anybody wants to talk about.
And you don’t have to be here live to be able to listen to this. You can actually get the full feed of Astronomy Cast, so I’m sure there’s a link somewhere. Do a search for Astronomy Cast full feed. You should be able to find that as a podcast and hear us ramble for another half hour if this isn’t’ enough Astronomy Cast. Alright, Pamela, thanks as always, and we’ll see you next week.
Pamela: Sounds great, Fraser. See you next week.
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Duration: 28 minutes