First AuAu Collision in STAR at Full RHIC Energy


Collision of Au+Au simulation by the research collaboration group UrQMD. The two gold nuclei, as viewed in the laborartory frame of reference, are Lorentz contracted along the direction of travel. Neutrons are depicted in white, protons in red. Pions, the most abundant of the produced particles, are green.
Click on the image for animated view (MPEG format, 867K).

Current Projects

STAR - a first generation experiment at the Relativistic Heavy Ion Collider (RHIC). Gold beams of 100 GeV/nucleon each will collide, providing conditions sufficient for the production of the quark-gluon phase of matter. The Purdue High Energy Nuclear Physics group has played a central role in the development, testing, and installation of the Time-Projection Chamber, the main detector of the STAR experiment.

The group played a leadership role in data analysis and physics interpretation. We analyzed particle production using macroscopic quantities of statistical mechanics (temperature, chemical potentials, etc.) and concluded that relative particle abundances are fixed by a single temperature of about 165 MeV. We also found that the produced particles are moving collectively with a high average speed, about half of the speed of light. We pioneered the analysis of medium modifications to energetic jets (collimated shower) of hadrons due to interactions between jets and the high temperature and density medium. We discovered that the modified jet-correlated particles prefer a conical emission pattern, suggesting the formation of supersonic Mach-cone shock waves in subatomic world.

PREVIOUS PROJECTS

EOS Collaboration - a reverse kinematics experiment in which Gold, Lanthanum, and Krypton 1 A GeV projectiles bombarded a Carbon target. This experiment features a seamless series of detectors capable of providing complete charge reconstruction of each collision. Results to date are consistent with a continuous phase transition occurring over a narrow range of excitation energy deposited in the projectile.

E895 - a continuation the EOS Collaboration Bevalac flow studies extended to higher energies.

E864- a search conducted at the BNL Alternating Gradient Synchrotron (AGS) for long-lived (> 50 ns) strange quark matter. Strange quark matter (SQM), matter comprised of roughly equal numbers of up, down, and strange quarks, may be the ultimate ground state of nuclear matter. Even if SQM is not absolutely stable, it may be stable against strong decay, decaying  via the weak interaction. If this is the case, central collisions between two heavy ions may provide the necessary conditions to create a "strangelet." The E864 spectrometer has redundant tracking in both space and time, and a spaghetti calorimeter that provides a "late-energy" trigger, allowing us to enhance the sample of events that are likely to contain strangelets.

E442 - an inclusive proton-nucleus experiment conducted at the Internal Target Area at Fermilab in 1977. Using a supersonic gas jet of hydrogen mixed with varying inert gases, Xenon, Krypton, Argon, we studied the systematics of the kinetic energy spectra of fragments as a function of mass, charge, and production angle. The experimental evidence suggested that intermediate mass fragments of charge > 3 originated from a common system, i.e. a simultaneous disassembly.

E591 - an inclusive proton-nucleus experiment, also conducted at the Internal Target Area at Fermilab in 1981, featuring high statistics and low energy thresholds for dectection of heavy nuclear fragments. The capability of detecting low energy multiply charged reaction products such as carbon, oxygen, ... was crucial to deterimining the total yield of each fragment type.

The main experimental result was the observation of the power-law yield in the fragment mass distribution. The power-law characterizing the inclusive mass yield distribution had an exponent of -2.6, within the range expected for a system undergoing a continuous, or second order, phase transition. The fragment isotopic yield was well-described by adapting the Fisher droplet formula for nuclear physics. The Fisher droplet formula is a highly successful model of liquid-gas phase transitions in the neighborhood of the critical point. We estimated of the temperature of the system to be 5 MeV. Incident beam energies varied from 30-350 GeV. No energy dependence in fragment production was observed in this, the limiting fragmentation regime.

E778 An inclusive gas jet experiment conducted at the Brookhaven National Laboratory (BNL) Alternating Gradient Synchrotron (AGS) in 1986. Fragment production in xenon was studied as a function of incident proton energy over the range 1-20 GeV. As much as a ten-fold increase in fragment production was observed over this energy range. Evidence for binary breakup at low incident energies was observed. The energy dependence of the Fisher droplet model quantities was determined permitting the approach to the critical point to be explored.

E735 A proton-antiproton collider experiment conducted at the Fermilab Tevatron in 1987. This was one of the first examinations of very high multiplicity events created in pbar-p collisions at center-of-mass energy 1.8 TeV. By triggering on high multiplicity events and sampling particle spectra for pions, antiprotons, kaons, lambdas..., we were able to study the energy density dependence of the transverse momentum spectra and yields. A Hanbury-Brown and Twiss analysis of the pions permitted us to study the energy density dependence of the source size.