Heavy-Ion Collisions & Other High-Energy Physics News from Brookhaven National Lab
Institutional Feature, January 2011
Is RHIC itself being upgraded, or just the STAR and PHENIX detectors?
We're upgrading STAR and PHENIX and also the collider itself. All three are getting upgrades. We're improving the luminosity of the collider, which basically means the rate at which collisions happen between the two beams. We're doing that with a technique known as beam cooling or stochastic cooling.
These heavy nuclei have very strong positive charges, and as you try to put more and more ions into a bunch—they're bunched together as they move around the machine—they have interactions among themselves because of this densely-packed positive charge. It tends to blow up the beam and the collision rate goes down. So this beam cooling technique is a sort of Maxwell's Demon-like effect to undo this problem.
How do you see the research on heavy-ion physics evolving now that both the LHC and RHIC will be doing this kind of physics?
Secretary Chu Tours the STAR
Detector
Courtesy of Brookhaven National
Laboratory.
Energy Secretary Steven Chu (center) tours the STAR detector at Brookhaven
National Laboratory's Relativistic Heavy Ion Collider (RHIC). Accompanying
Secretary Chu are Associate Laboratory Director for Nuclear and Particle
Physics Steven Vigdor (left) and Laboratory Director Sam
Aronson.
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We think a lot of excitement will come out of the early measurements at the LHC. Just the bulk properties of the matter created there will tell us a lot. We've raised this question before of whether the matter looks more like a liquid or an ideal gas, and that will come out of the early measurements at the LHC. In one of these collisions, thousands of particles are produced, and seeing exactly how many are produced is relevant to this question of what the thermalization mechanism is and what the initial state looks like, whether gluon densities are (or become) saturated. We think there will be a burst of excitement in the next year about this.
Then the LHC will start focusing on what we call hard processes—things like jets and producing heavy flavor quarks. RHIC will focus more on three things. One is just taking the very large data samples that are needed to address questions about these symmetry-violating bubbles, for instance. For that we're looking at very subtle phenomena, and we need to look at samples containing billions of events. We need to run a long time and have heavy-ion collisions as our primary mission.
The second thing will be searching for this critical point I talked about, and that requires lower energies that can be run at RHIC, not the LHC. The third thing is that RHIC is really going to try to quantify the properties of this matter we observe. What is the temperature? What is the viscosity? Can we determine the speed of sound and what are called transport coefficients, which determine the rate that energy is lost by quarks traversing this matter? To do these things, we need very large samples, and that's an effort better suited to RHIC and its dedicated, long heavy-ion collision runs.
As for the ongoing program with polarized protons, that is unique to RHIC. No other collider in the world has these polarized protons. Resolving this question of where the spin of the proton comes from relies on RHIC.
We're also aiming to add an electron accelerator to RHIC so we can collide electron beams with the heavy nuclei and polarized protons. That will allow us to do much more detailed mapping of these gluon densities, to really see if this saturation sets in. It will let us study the initial state in these heavy-ion collisions. That's the sort of direction RHIC will be moving, while the LHC will be focusing on understanding the properties of matter at its higher temperature and really focusing on the energy loss of quarks and gluons in traversing this matter.
LHC is also an exploratory machine. What it will do is produce matter probably at factor of two to three higher temperatures than we produce at RHIC. We don't really know how the quark-gluon matter evolves with temperature. What we see in the early collisions will to a large extent determine what the priorities are for subsequent runs. RHIC has a well-defined program of measurements to quantify things we've already seen, while the LHC is in more of an exploratory stage right now.
Brookhaven National Laboratory
Steven Vigdor, Nuclear & Particle Physics
Upton, NY, USA
BROOKHAVEN NATIONAL LABORATORY'S MOST CURRENT MOST-CITED PAPER IN ESSENTIAL SCIENCE INDICATORS:
Yao WM, et al., "Review of particle physics," J. Phys. G-Nucl. Particle Phys. 33(1): 1-+ Sp. Iss. SI July 2006, with 2,958 cites. Source: Essential Science Indicators from Thomson Reuters.
ADDITIONAL INFORMATION:
- Menu for the institutional interview series with Brookhaven National Lab from the Special Topic of Hadron Colliders.
- View the Special Topic of Hadron Colliders Research, 2000-2010 (Nov. 2010).
KEYWORDS: BROOKHAVEN NATIONAL LAB, NUCLEAR PHYSICS, PARTICLE PHYSICS, SYNCHROTRON LIGHT SOURCE, CLIMATE MODELING, ENERGY PRODUCTION, HIGH-TEMPERATURE SUPERCONDUCTORS, RHIC, RELATIVISTIC HEAVY ION COLLIDER, QUARK-GLUON MATTER, QUANTUM CHROMODYNAMICS, BIG BANG, MATTER/ANTIMATTER ASYMMETRY, PHASE TRANSITION, EARLY UNIVERSE, PARITY, CHARGE PARITY, STRING THEORY, BLACK HOLE PHYSICS, DEGREES OF FREEDOM, FRICTIONLESS LIQUID BEHAVIOR, SYMMETRY-VIOLATING BUBBLES, POLARIZED PROTONS, STAR, PHENIX, LARGE HADRON COLLIDER, LARGE DATA SAMPLES, CRITICAL POINT, MATTER PROPERTIES, ELECTRON ACCELERATOR.