Decades after the Standard Model of physics was developed, a missing key may have been found.
Kyle Cranmer, an experimental particle physicist and New York University professor, talked about the importance of the Higgs Boson particle in physics during his TEDx talk Sunday. In the mid-20th century, physicists developed what we call the Standard Model, an all-encompassing theory that sought to explain the laws of nature. The Standard Model is incomplete, though, and one of the keys to completing it is the inclusion of the Higgs Boson particle.
“We have thousands of collaborators all over the world looking for this particle,” Cranmer said.
On July 4, 2012, scientists at the European Organization for Nuclear Research (CERN) discovered a particle that might be the Higgs. The next day, The New York Times’ front page read, “Physicists Find Elusive Particle Seen as Key to Universe.” Cranmer said he bought around 40 copies.
Cranmer’s role at CERN was twofold: he looked for a specific way that the particle decayed and he analyzed the combined work of other scientists looking at other types of decay at the same time.
“The Higgs decays almost instantaneously and there haven’t been any around since the Big Bang,” Cranmer said.
A proposed idea of physics Cranmer is keen on is supersymmetry. In nature, smaller things, such as snowflakes, tend to be more symmetrical than larger things. The idea was first proposed by German mathematician Emmy Noether. Cranmer wonders if the principle still applies to particles, our smallest objects in nature.
“Symmetry can enhanced as you get to smaller and smaller scales,” Cranmer said. “By the time you get to the atom, symmetry is the rule rather than the exception.”
If that kind of symmetry — what physicists call the Minimal Supersymmetric Standard Model — is proved correct, then physicists may have a new model beyond the Standard Model we have been working with for decades. The only problem, though, is that supersymmetric particles, or “sparticles,” have not yet been observed.
Cranmer is looking forward to continuing this kind of research at ATLAS, a lab at CERN where he works. He showed the audience a 3D graphic of CERN’s location and where ATLAS was in relation to the LHC. As Cranmer sees it, the groundbreaking science — this “triumph of human curiosity” — that he’s involved in highlights how research can be a good investment. After all, as Cranmer points out, the World Wide Web was also developed at CERN and given to the world for free. He laments the decline of U.S. involvement in scientific research, citing the Superconducting Supercollider that was nearly built 20 years ago in Texas before Congress pulled funding.
“If we would have built it then we would have found the Higgs Boson 10 years ago,” Cranmer said.
Pipe Dream: What was your precise role in the discovery of the Higgs Boson?
Kyle Cranmer: The Higgs can decay in a bunch of different ways. And each way it decays looks different in our detector. And so there are a bunch of different groups of people looking out for a specific way it might decay, and so they become experts in this particular way. I worked on one of those particular ways that it decays, but the main role that I had was then taking all of these individual searches and taking them together into one big, combined analysis of what’s going on. And that’s what we do at the very end when we were claiming discovery. So a lot of my work was somehow trying to take the different pieces of all these individual groups and trying to take it together into one cohesive analysis.
PD: In terms of the search for the Higgs itself, how does the search for all of these different ways of decaying balance out against the other features that the Higgs – as conceived at that time – supposedly had?
KC: In the theory, we don’t know beforehand what the mass itself is. So as you change the mass, the relative fraction of the time that it decays in one way or a different way changes. That makes it a little bit tough because you don’t necessarily know exactly what to look for, but you have a sort of template with one dial, which is the Higgs mass. So we had to kind of scan along this Higgs mass and at each point, we sort of knew what to look for, and then we would work together to try to cover all those bases.
In some places it’s very easy to see and in other places it’s very hard. Where we ended up finding it was a place where it really required combining many different decays and things like that.
PD: I read [in an essay by Nobel Prize-winning chemist Steve Weinberg who conducted early research leading to the search for the Higgs Boson particle] that the Higgs mass is very small compared to other key figures in physics, such as the Planck mass. Could you please talk about that a bit?
KC: Right, so in most ways it’s actually heavier. A unit of mass is GeV. A proton, for example, weighs one GeV, an electron is much more smaller than that. Most of the particles are kind of in that neighborhood. And then we have particles that are roughly 100, and there’s this thing called the top quark which is like 175. So we found the Higgs at 125. So it’s actually a fairly heavy particle, but it’s actually the second-heaviest that we know of.
But what’s weird about it is that, in the theory, it naturally wants to be really heavy. And that’s what the idea of the Planck mass and the Planck scale comes in. And that’s an energy scale where gravity and quantum mechanics come together on equal footing, and that’s where often is the business of things like string theory and stuff like that. So we don’t understand the physics at that scale, but the Higgs Boson would want to naturally be more heavy, like billions of billions of times heavier than we actually see it. So the mystery in some sense is actually why it is so light.
PD: How does the difference in weight from what you expected to what you actually found effect the theory as a whole?
KC: Well we didn’t really already know what the mass was going to be, so it could have been almost anything. But it does make a big difference. It’s not just some number – it turns out that if you wanted to start this problem that I was alluding too, that why is the Higgs not really heavy – that’s a problem we call the “hierarchy problem” or the “naturalness problem,” that it naturally wants to be incredible heavy but instead we find this much lighter mass. So if you want to solve this problem then people invoke all new kinds of theories. Things like supersymmetry. And in those theories, it’s actually difficult for the Higgs to be as heavy as it is.
So right now we’re in this interesting time where the field of physics is sort of looking at two paths. One is where you have something like supersymmetry around, which we haven’t seen yet, which would be a huge step forward in our understanding of nature. And another where there’s nothing like that but we have this unresolved problem, this naturalness problem, or hierarchy problem, and that’s what Steve Weinberg was alluding to.
And if nothing else happens, then it will be a real puzzle for physics why the Higgs has the mass that it does, if we don’t find anything else. And that actually ends up prompting people to talking about the idea of the multiverse, the idea that there might be a bunch of different universes out there and each of these different universes will look very different, but most of them will not support life. Since we’re here and we’re alive, then we’d naturally expect to find one that has this peculiar property, and Steve Weinberg actually called that the “anthropic principle,” and he used that to explain some things about cosmology.
So it’s a very highly controversial idea right now in physics because we usually look for a kind of explanation and this is us saying that there’s not really an explanation. There’s this kind of selection-pressure that we’re here to observe the world. We’re here on Earth where there’s water as opposed to us being, you know, on Jupiter or something because it’s not quite right to support life. So anthropically, you wouldn’t expect to find yourself on Earth.
PD: Could you please tell me about your time at CERN?
KC: I lived out there during my graduate studies – almost six years total – and since moving to New York I fly back and forth quite a bit. It’s a super exciting multinational place. There are people from 40 different countries around the world that have come to this lab and it’s really great to see how science is the opposite of politics. You have people from Israel and Pakistan and Iran and wherever talking the same language about physics, and they can get along.
PD: The space itself spans a couple of countries, doesn’t it?
KC: Well the lab is primarily in Switzerland but the accelerator itself is so big that half of it is in France and half of it is in Switzerland.
PD: You said that you still fly back and forth there – to what degree are you still involved in the research?
KC: Oh I’m very involved. Most people are not based on the lab because they are also professors or something around the world. Most people are doing research and a lot of the time they do it on their computer at their home institute and then they fly to CERN when they need to or when they can. I’m very involved in the research and I travel out there quite a bit, but it’s not a requisite to actually be sitting there at CERN.
PD: What are you working on right now?
KC: Right now we’ve found this particle and we’re trying to measure its properties and see if it’s really the particle that was predicted in this theory that we have called The Standard Model. If we see deviations from that, then there’s a sign that something else is going on, and that would be very exciting. In our first measurements of these properties, we actually see some tension between what this data says and what the theory predicts. So as we take more data, it’s a question of whether that difference will subside or whether it will become more significant, in which case we’ll be able to see something really interesting about new physics out there.
PD: Which one are you hoping for? Are you hoping it will differentiate from the standard model or—
KC: Yes, definitely. We’d definitely like to see some new physics and find some new things that we can hope to understand. For instance, this theory that we have – that’s so great – it still doesn’t explain what dark matter is, and we know that there’s dark matter out there. And so we need a bigger theory and this hierarchy problem that we’ve talked about it really something that we’d like to see addressed. And so definitely, I’d love to discover more things, and there are some very well-motivated things that we might still see.
PD: Is there anything else that you want to talk about?
KC: One thing that people should keep in mind is that [CERN] is based in Europe and the US used to have flagship colliders – we had the FermiLab, and we had the Teletron, and before that we were going to build something called the Superconducting Supercollider. It was cancelled and if we would have built it then we would have found the Higgs Boson ten years ago. In terms of what’s going on in science today, the US is definitely in some sense losing in leadership. However, people shouldn’t also shouldn’t think that the fact that the accelerator is based in Switzerland necessarily means anything. It’s a big international effort – the US is very involved, it’s one of the big international contributors to this experiment, so Americans should be proud of our contribution and not think that it was the Europeans that found it. At the same time, we are somehow giving away what we used to have as a leadership role.