Heavy-Ion Collisions & Other High-Energy Physics News from Brookhaven National Lab

Institutional Feature, January 2011

Steven Vigdor from Brookhaven National Laboratory

Associate Lab Director for
Nuclear & Particle physics at
Brookhaven Dr. Steven Vigdor.

According to Essential Science IndicatorsSM from Clarivate Analytics, Brookhaven National Lab ranks at #20 among the 681 institutions comprising the top 1% in the field of Physics. Brookhaven's record in this field includes 4,045 papers cited a total of 96,483 times between January 1, 2000 and August 31, 2010.

In our Special Topics analysis on Hadron Colliders research over the past decade, Brookhaven ranks at #1 by total cites and #2 by number of papers, based on 1,529 papers cited a total of 27,320 times.

Established in 1947, Brookhaven is a US Department of Energy Lab located in Upton, NY, and is operated by Brookhaven Science Associates. Brookhaven currently has over a dozen research facilities, including the Relativistic Heavy Ion Collider (RHIC), Alternating Gradient Synchrotron, and the Center for Functional Nanomaterials.

In this interview, ScienceWatch.com correspondent Gary Taubes talks with Dr. Steven Vigdor, the Associate Lab Director for Nuclear & Particle physics at Brookhaven, about the Lab's achievements in physics in recent years.


SW: How much of the significant research coming out of Brookhaven in the last decade is RHIC physics and how much comes from other researchers?

A lot of it is RHIC, but by no means all. We still have an operating synchrotron light source. We're building a new generation of light source right now. There has been a lot of high-profile research coming out of that facility as well.

We also have pretty high-profile research on things like climate modeling, basic energy production, and a lot of work on understanding high-temperature superconductors. The laboratory has also done groundbreaking brain-imaging research on drug addiction and obesity that has captured worldwide attention. But so has the research from RHIC: press releases on RHIC results have garnered strong worldwide coverage, and the reports in the scientific literature have been widely cited.

SW: What would you consider the major results out of RHIC, the press-release-worthy news?

Certainly the biggest thing—and what we've had some press releases on—is that we do seem to produce at RHIC, as it was originally intended to do, quark-gluon matter. This is matter in which neutrons and protons have melted and the primary constituents are quarks and gluons. But that matter behaves nothing like the original predictions.

Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) is composed of hundreds of linked magnets. Shown here is an end view of a RHIC superconducting magnet prior to final assembly.
RHIC Magnet
Courtesy of Brookhaven National Laboratory.

Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) is composed of hundreds of linked magnets. Shown here is an end view of a RHIC superconducting magnet prior to final assembly
.

The interview series with Brookhaven National Labs  >

The original predictions were based on a feature of the strong force—of the theory we call quantum chromodynamics (QCD)—that predicts that at very short distances, the force between quarks gets very weak. Because of that, we thought that if we create quark-gluon matter, we will get unique matter, a dense gas comprised of non-interacting particles, the quarks and gluons. They'd be very densely packed, but essentially independent of one another. That was the prediction.

What we observe is matter with very strong correlations, matter that flows essentially like a frictionless liquid, a very different extreme from the ideal gas predicted. This has relevance for the state of matter in the early moments of the universe, about a microsecond after the Big Bang, when it passed through temperatures and energy densities comparable to what we produce at RHIC. The difference, of course, is that at RHIC we produce it on a microscopic scale—the size of a nucleus. That's the biggest-impact result we've had, and then we've been learning lots of other things about this matter.

SW: Has this changed how astrophysicists or cosmologists think about the origin of the universe?

Not that much. What's potentially more relevant to cosmology is a more recent result that came out just last year. One of the really critical questions in cosmology about the early universe is one of the leading questions in nuclear and particle physics research right now. This is about how matter vs. antimatter asymmetry was established in the early universe.

In models of the Big Bang, it starts with a burst of energy, and that energy is converted to mass. In the conversion, equal amounts of matter and antimatter are produced. So we obviously have an imbalance present in the universe today—we see lots of matter and essentially no anti-matter. How did that happen? That's not easy to understand. The conditions to understand it were laid down 40 or 50 years ago by Andre Sakharov, but how those conditions were achieved in the early universe is the question.

Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) uses a system of intense radio waves to give the particle beam a little extra "kick" of energy to accelerate it each time it travels around the ring. This is called the radio frequency, or RF, system. The RF cavity system is shown here.
RF Cavity System
Courtesy of Brookhaven National Laboratory.

Brookhaven National Laboratory's Relativistic Heavy Ion Collider (RHIC) uses a system of intense radio waves to give the particle beam a little extra "kick" of energy to accelerate it each time it travels around the ring. This is called the radio frequency, or RF, system. The RF cavity system is shown here
.

The interview series with Brookhaven National Labs  >

Leading speculation argues that there was a phase transition in the early universe, not the one we study at RHIC, but an even earlier one, during which bubbles were created, like bubbles in boiling water. And inside those bubbles, what we call violation of baryon number conservation could be established. That means it could have produced an imbalance between the number of quarks and anti-quarks, and those bubbles play a critical role in establishing this matter/anti-matter asymmetry.

Okay, that's speculation. At RHIC, we're studying a slightly later phase transition, one that occurred at somewhat lower temperature. But it turns out that there's an exactly analogous type of bubble we can look at. And in that analogous type of bubble, instead of getting an imbalance between the number of quarks and anti-quarks, we get an imbalance between the number of left-handed quarks and right-handed quarks.

SW: Okay, you'll have to explain to us what you mean by left- and right-handed quarks.

Quarks have an intrinsic spin; you can think of them as spinning like a right-handed or left-handed screw. Either the spin is opposite their direction of motion or along it. So we can produce these bubbles in this very hot matter near the phase transition where we could get an imbalance. And that imbalance at RHIC would give rise to a violation of symmetry principles that normally describe quarks and gluons. These symmetry principles are called parity and charge parity.

There were predictions about what the observable effects of this would be in RHIC collisions, and we now see behavior that is very consistent with those predictions. We still have to rule out whether there might be more mundane explanations, but this has generated a lot of excitement because it looks as though this may be a way of actually studying the formation of these symmetry-violating bubbles, which, in the current models at least, play a very important role in cosmology, in getting to that matter/anti-matter symmetry.

That finding is what cosmologists are paying quite a bit more attention to. The liquid behavior verses ideal gas behavior is something they find interesting, but the people who are really excited about that are string theorists.

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