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Local Scientists Help Discover New Subatomic Particle

July 4, 2012 1:15 p.m.


James Branson, Physicist and UCSD Professor.

Related Story: Local Physicists Help Discover The 'God Particle'



ST. JOHN: This is KPBS Midday Edition. I'm Alison St. John in for Maureen Cavanaugh, it's Wednesday, July†4th. We heard on NPR this morning that scientists actually shed tears today at the announcement that researchers have discovered evidence of the long-sought Higgs Boson article. It's being hailed as possibly the most important breakthrough in physics in 40 year, and it turns out that several scientists from UCSD were involved in the discovery. We have one of them here in-studio to help us comprehend what this is, and what it means for our understanding of the universe. Jim bran son, thank you so much for joining us.
BRANSON: Nice to be here.
ST. JOHN: And you, Jim, just got back from Geneva last night; is that right?
BRANSON: Yeah, I flew in about 9:00†PM last night. Our analysis work was already done, and I knew it was going to be an hour-talk, but I was interested in the talk from the other experiment that came at midnight last night.
ST. JOHN: Let's talk a bit about the bigger picture and your personal contribution to it. But what does this mean to you personally as a scientist?
BRANSON: Well, to me personally, I've been looking for this particle for a long time. Since DSSE was proposed in the United States , I was involved in an experiment, and I was interested in this low-mass Higgs search. We searched for it everywhere. But I expected it to be at low-mas, we expected it to be at low-mass, so I've been pushing in this channel Higgs to gamma gamma for the last 20 years, really.
ST. JOHN: So do you think this is it? There seems to be a lot doubt about it.
BRANSON: Well, we have to be careful because we found a narrow resonance where it's certainly the most likely explanation for this is that it is -- the Higgs particle is something for like the Higgs particle. There's different versions of it that we could have. But we haven't measured many properties of the particle yet, other than it's there. So we need to measure the decays into several different channels, and the production mechanisms. And we will then pin down that it is the standard Higgs particle, or it's probably some variant of it with slightly different properties that are even more interesting.
ST. JOHN: Okay. So now we know that this is big. Can you do your best to explain to us whys so significant?
BRANSON: Well, it's a really complicated problem. And there's a lot of reasons that one should be interested in it. And you can pick from that list. But I would say it's a key element of the laws of physics that understand the fundamental laws of nature, and really, we've discovered two types of particles before, two different spin particles N. 1905, we realized that the photon made up electromagnetic radiation, and it was spin 1. And later we discovered spin 1/2 particles, so we found particles that were energy, and particles that were matter. Now we have a third type of particle which is spin 0. And it's neither energy nor matter, but it really can change the vacuum. And the Higgs particle changes the vacuum of the universe into the universe we know. Before that, it was something different.
ST. JOHN: It changes the vacuum. So one of the things, the words that's being tossed around is mass. So I start thinking about materializing reality. Is it anything to do with how we actually materialize reality?
BRANSON: Well, after the big bang, as we understand it, as we understand the laws of nature, all the particles were massless. In terms of quantum field theories, we can have a quantum field theory of a massless particle, a spin 1 massless particle, for example, but we can't have a good quantum field theory of a massive spin 1 particle N. The Higgs mechanism, we give mass to all the particles. Before the Higgs changed the vacuum into the new Higgs vacuum, all the particles were massless like the photon, flying around at the speed of light, and not making anything. So it would be just be particles flying around at the speed of light and not being able to make any kind of complex object. And then we got masses and we can have elements and atoms and nuclei and things that were made out of it.
ST. JOHN: We were talking about the interview of the faaccount that without that, perhaps one would be able to put your hand through a door, that the solidity of the universe depends on -- we were questioning this, whether this might be one way to understand it.
BRANSON: I think the difference between spin 0 and spin 1/2 particles, spin zero particle, you could put their hand through them, like two light beams could go right through each other. Spin 1/2 particles, you cannot have two of them in the same place. But spin 0 is an entirely new and different thing that we've never seen before.
ST. JOHN: So let's just get back to what your particular contribution was. I think it's interesting. There were four scientists from UCSD who have been very much involved for 20 years or so. What was your element of it?
BRANSON: The four of us were involved in slightly different things, although all of us worked on the Higgs search. Sharma and I concentrated on the Higgs search. But I concentrated even more on the Higgs search into gamma gamma because I was basically betting with my research time that that was the mode where it would be most easily seen. And it turned out to be true. Both experiments, that's the strongest signal. It's also seen in Higgs 2, ZZ, into four electrons, which is a nice clean signal, but not as such a strong rate.
ST. JOHN: All right. Were you leading a group that samples trails? Proton-proton collisions
>>> Basically that's what the whole group does. And the analogy is that we have a 100 megapixel camera, and we take a picture every 50†nanoseconds. So it's an incredible video camera, and now we're trying to take information from this camera and reconstruct the events that happened every 50†nanoseconds. Actually we get now about 30 events, 30 collisions in every one of these 50-nanosecond pictures, and one of them could be one of these Higgs. In the Higgs to gamma gamma channel, we have about 150 of these events that we've found. It's been running for years, taking picture, and just a small number are these Higgs to gamma gamma events. And we analyzed the data with large computers to dig out these signal, like from a video.
ST. JOHN: Did you ever see these collisions?
BRANSON: One of the things that avia gill does, he's in charge of a group that visualizes the events. So we turn all the data we get into pixels, and we see tracks of the particles coming out. There are hundreds and hundreds of particles coming out in one of these collisions. And we tag the ones that are really interesting, like the photon, the high PT photons or leptons.

ST. JOHN: And you're trying to get back to what that particle is based on the parts that have spun off from the collision. And you've been analyzing this data almost ten years back?
BRANSON: Well, the LHC is run for three years now, really successfully. There was a little explosion several years ago where one of the superconducting leads blew up and damaged a lot of the accelerator. And we have most of our data from this year and last year. And we've been analyzing that. And a lot of that analysis goes on at UCSD. We have a tier-2 commuting center in the physics department, and we run a lot of the commuting. And a lot of the analysis of Higgs to gamma gamma happened there.
ST. JOHN: Interesting. It did happen in Europe, but how many American scientist ares would you say contributed to this?
BRANSON: In the experiment I'm in, CMS, there are about 600-7 hundred American physicist, a lot of them are graduate students and post docs. And they're probably about the same number in the other experiment which is called atlas. Both of these experiments saw very significant observations of this Higgs particle combining last year's and this year's data.
ST. JOHN: Are there a lot of scientists right here in San Diego who have been fairly closely involved celebrating today?
BRANSON: There's four faculty at UCSD, and another key player has been Marco Pierry who's our only research scientist. Sort of like a faculty level, but he's full-time on research. He played a key role. And he's actually a convener of the Higgs to gamma gamma group now. Then we have a group of about 25 physicists from UCSD working on the experiment.
ST. JOHN: During the announcement, the spokesman said this is it a prelim iary result, but we think it's very strong and solid. What's the quote. So what are the chances that further research might disprove that this is a Higgs?
BRANSON: Well, I think statistically now the evident is very strong. Two experiments at the 5-signal level, which in principle, statistically means about one part in 30 million to be wrong for each experiment, which is pretty strong statistical evidence. But I think the data -- we haven't seen the other experiment's cata until last night. So it's very fresh, the comparison. There's some slight differences, but they're almost exactly the same. We're going to get a lot more data this year, and we will have pinned down both -- worked out all the systematics and done a lot of checks with the other experiment, and measured some of the properties of this particle presumably by the end of 2012, and then we'll know -- I don't think it's going to turn into nothing, but it could turn into something slightly different. And we're all very happy, we think almost for sure we have something. But it's reasonable to take a little bit of time and do some checking at this point.
ST. JOHN: But what was it that made you all decide that now was the moment to say we've got it? Did something actually come together? It sounds like you were even quite surprised at what you saw from the other team.
BRANSON: I think I was surprised that we had evidence now. I thought -- I was maybe a little bit pessimistic that we would be done. But what actually happened is a big international conference in high energy physics once in the summer every year, the biggest conference of the year, and we knew that both experiments would make results for the conference. We did a blind analysis in all these channels. We didn't look at the signal region. We developed the analysis perfectly then we opened the box before the conference. And we saw more than we expected, particularly I'd say in the Higgs to gamma gamma channel. We really saw more than we expected. So we knew this both experiments were going to do it, so the lab organized this meeting to bring the data together. We didn't know that we would have what we call strong evidence and observation. We're trying not to use the discovery word quite yet. But with both experiments coming with an observation, essentially the same mass, essentially the same signal strength, it looks pretty clear.
ST. JOHN: Now, you were obviously very excited. How hard have you been working the last few weeks or months?
BRANSON: Well, I've been working very hard. Some of the younger physicists may have been working harder. Our normal workday is 16 hours a day, and 6 or 7 days a week. But I know that there were some young physicists who weren't sleeping much at all fairly week at a time. They must have gotten a couple hours here and there. But people were getting a little bit crazy, I would say.
ST. JOHN: When you're working, is it mostly in front of the computer analyzing data?
BRANSON: Yeah, the interface to almost everything is the computer. Not only programs to analyze the data but to make pictures, to write papers. They're 200†pages in journal notes about analysis that we make and review, and other people comment on and criticize. The collaboration looks for holes in these things and the interface to everything is the computer screen, I'm afraid.
ST. JOHN: Are you working with scientists from all over the world?
BRANSON: Yeah, there are huge collaborations. There are good points and bad points. You can't take over the whole thing. We have about 2,600 physicists in CMS. Again, I won't get the number exactly right. From all over the world. Europe, Asia, the United States , Latin American. Basically everywhere.
ST. JOHN: And is there any competition between countries on this one?
BRANSON: The toughest competition is between the two experiments. We'd really like to beat the other experiment, we'd like to prove them wrong, and they'd like to do the same to us. Turns out we got the same result. And
ST. JOHN: Wow!
BRANSON: And I think it's obviously good to have this kind of competition with a little bit of secrecy. So each experiment makes its result just as well as it can, and then it's checked by the other experiment. It's a $10†billion accelerator. The experiments cost about $1†billion each to build. And I think two experiments is the right amount to do the checking properly.
ST. JOHN: Okay. So you said to me you're going to go right back to work. It's not like anyone is going to stop here, right?
BRANSON: Well, I stopped to do this. I'm actually trying to analyze the signal right now. We're now looking to see if there are unusual things about the signal. So after opening the box, we got our first chance to look at the events, and we're trying to see if there's something unusual about it.
ST. JOHN: And in the minute that we have left, if it turns out that it isn't quite what you expected, could that be even more interesting?
BRANSON: It certainly will be more interesting if it's not exactly what I would call the minimal standard model Higgs. There's also expansions of the standard model Higgs with more particles that behave as the single Higgs might. In supersymmetry, we expected this low mass, so this could be the gateway to supersimistry. And supergravity and superstring theories.
ST. JOHN: I wish we had more time to explore that, but we'll have to leave it this. Thank you so much.
BRANSON: It's been a pleasure.