“What in the world are we doing here?” The question has haunted mankind since the beginning of time.
Finding an answer may be a tedious job but someone’s got to do it.
Enter Brandon Drummond, a physics graduate student who is two years into his doctoral program. As a research assistant for Professor Joseph Izen, Ph.D., he primarily functions as an analyst for the folks working on the BaBar experiment.
BaBar, an international collaboration of 600 physicists and engineers, investigates the nature of matter and the laws that govern it.
You may have heard about The University of Texas at Dallas’ connection to the experiment: The High Energy Physics Group, led by Dr. Izen and consisting of Professor and physics department head Dr. Xinchou Lou; Ph.D. student Glenn Williams; and research scientist Dr. Shuwei Ye, who did a yeoman's job in their recent discovery of a mysterious new subatomic particle they named Y(4260). The group’s research is funded by the United States Department of Energy.
Colliders and accelerators
“When we call it a particle collider, it makes it sound like we’re slamming single particles together. But these are beams [of particles] pointed at one another. They travel in bunches, and they are continuously being fired at each other and stuff is continuously coming off from it. And we sit down and watch the data come in,” Brandon said.
“To actually take beams of particles and collide them [is amazing],” Brandon said. “We are talking about the tiniest of the tiny [subatomic particles]. Physicists have to aim subatomic particles and make them hit head-on from a distance of more than 3 kilometers. Lots of hardcore engineering goes into it.
“Everyone involved in the experiment chooses a particular [particle] decay to look at. There are so many different things going on inside [the accelerator] that you pick just one particular thing to look at and ignore all the others,” Brandon said.
When a particle decays, it must obey the laws of physics, which include certain conservation rules. For example, energy must be conserved – the total energy of all decay products must be equal to the total energy of the original particle. This means a particle decays to two or more particles whose total mass – the measure of the amount of material it contains – is less than that of the original particle.
“I’m actually looking for higher resonances – like this Y(4260) that just came up and the X(3872) that came out about a year and a half ago. We are calling them higher resonances – we keep looking higher and higher in the mass range and finding newer and newer things,” he said.
BaBar is more than an elephant
The experiment is called BaBar for a reason. BaBar stands for B meson and anti-B meson, which is written , hence B-Bar or BaBar.
“We study the B meson decays. There’s the B meson and the anti-B meson, and we study all the byproducts of these B mesons. I’m looking at B goes to XK, where X could be one of those higher resonances. I just started that about six months ago or so,” Brandon said.
The term meson refers to any particle containing a quark-antiquark pair.
A B meson, for instance, consists of a bottom quark and either an up or down quark.
According to Brandon, the thrust of BaBar is to study something called charge conjugation (C) and parity (P) violation, or CP violation.
“CP violation really boils down to the creation of the universe during the Big Bang. Theoretically speaking, the creation of matter and antimatter should have been equally likely. However, if we look around, the universe seems to be heavily dominated by matter.
Matter versus antimatter
“Antimatter obviously behaves differently than real matter. And that’s really the basis of study, to understand that difference. Why is there matter in the universe? That’s the question BaBar started out trying to answer,” Brandon said.
Brandon continued to explain the nature of matter.
“The world that we live in is pretty much governed by electromagnetic and gravitational forces. We don’t really deal much with the weak and the strong force, the nuclear forces that bind the nuclei together and govern its decay.
“When you get down into the subatomic level, the distances are so small that those forces far outweigh gravity – gravity has nothing on these guys. Their world is a little different," Brandon said.
Under the standard model, there are really only a few distinct particles, Brandon said. They are only mildly different from each other in certain quantum characteristics, he added.
Processing the data
Brandon described a typical day at the office.
“My day-to-day activity involves a lot of computing. We have terabytes – one trillion bytes – of data that have been produced in this experiment and there’s more and more being produced all the time. You basically write an analysis program to look for what you are interested in and then you run through all the data at the Stanford Linear Accelerator Center (SLAC) hunting for things,” he said.
Brandon said the goal is to simulate data based on the models that are known at the time and then produce real data and look for discrepancies between the two. Where there are discrepancies, he said, there’s new physics.
Brandon said UTD produces a large number of these events and the data gets shipped back to SLAC via high speed network.
“There are many different detector sub-systems surrounding the epicenter of the collision. We call it the interaction point or the IP.
“One of the things they look at is the way the particle curves. The entire thing’s embedded in an electromagnetic field. As a charged particle comes out, it’s going to turn one way or the other based on its charge. It then hits the calorimeter and deposits energy. All of the sudden you know the charge, energy, and momentum of the particle. And you just take all these little pieces of information and once you have enough you say, ‘A-ha! That’s an electron or that’s a proton or whatever,’” Brandon said.
Summers at SLAC
Spending summers at SLAC is something of a perk for Brandon.
“The group here [at UTD] is small enough that they allow us to send a couple of people out to SLAC every summer.
“You get to work at a major international facility with scientists from all over the world. I hear four or five languages spoken in a single day when I’m there,” he said.
At SLAC, everyone has to put some number of hours sitting watch on the accelerator.
“This thing runs 24 hours a day, seven days a week so somebody has to be watching it, 24/7. Everybody chips in and we all run shifts sitting in the control room watching the data come off and just kind of making sure things look right,” he said.
Brandon said it can be nerve-racking sitting watch on an accelerator.
“I sit there,” Brandon said making a biting-nails gesture. “You get out there and you don’t know how things have been going. You can look at the logs – but you’re always worried something bad is going to happen.
“I’ve had the general stuff happen, where we will just lose the beam for whatever reason. And that sucks because we are trying to produce as much data as we can. We are in constant competition with other experiments so whenever the beam is down we are not doing the job we should be doing,” Brandon said.
The search for answers continues...
In the end it seems that plain old curiosity drives the particle physicist.
"I think we’d say that we do it for the pursuit of knowledge itself. That’s the general consensus.
"In our group, we don’t so much try make things up as much as we try to break things. So we take a theory and we try to disprove it more than we try to prove it, really.
"We have a professor in the physics department who loves the saying, 'A theory that can’t be disproved is not really a theory at all.'
"I think everyone in physics at some level has a deep questioning sort of personality or they wouldn’t be doing it. There is not a whole lot of incentive other than personal gratification of sorts. You are not guaranteed to make a lot of money or become really well-known in physics. You like what you do, you have an interest in being a part of it and you are sort of driven out of your own interests,” Brandon said.
- Updated: October 12, 2011