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Gary Westfall
University Distinguished Professor of Physics
Experimental Nuclear Physics
 
PhD, Physics, University of Texas 1975
Joined NSCL in September 1981
Phone(517) 908-7324
Fax(517) 353-5967
OfficeW204
 
Photograph of Gary Westfall

Selected Publications:
K/π Fluctuations at Relativistic Energies,
STAR Collaboration, Phys. Rev. Lett. 103,
092301 (2009)

Incident Energy Dependence of Correlations
at Relativistic Energies, STAR Collaboration,
Phys. Rev. C 72, 044902 (2005)

Fluctuations and Correlations in STAR, G.D.
Westfall, J. Phys. G: Nucl. Part. Phys. 30, S1389
(2004)

Narrowing of the Balance Function with
Centrality in Au+Au Collisions at = 130 GeV,
STAR Collaboration, Phys. Rev. Lett. 90,
172301 (2003)

Isolation of the Nuclear Compressibility with
the Balance Energy, D. J. Magestro, W. Bauer,
and G. D. Westfall, Phys. Rev. C 62, 041603R
(2000)
My research focuses on studying the quark-gluon liquid at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory using the STAR detector. At RHIC, we collide gold nuclei at center-of-mass energies of up to 200 GeV per nucleon pair. At this energy, the protons and neutrons in the incident nuclei are transformed into a hot, dense, and strongly interacting liquid of quarks and gluons. This quark-gluon liquid is a nearly perfect liquid, which has nearly zero viscosity as evidenced by the comparison of flow measurements to hydrodynamic calculations. The universe is thought to have existed in this form a few microseconds after the big bang.

The main detector of STAR is its time projection chamber (TPC). This TPC can produce a full three-dimensional picture of the collision of two ultrarelativistic nuclei. A collision of two gold nuclei is shown as measured in the STAR detector. Each line in the picture corresponds to a single particle leaving the collision. Several thousand tracks are observed in this one central collision. The color of the track represents the ionization density of the track. By correlating the curvature of the track and its ionization density, the particles that created the track can be identified.

The three cornerstones of the observation of the quarkgluon liquid at RHIC are thermalization, collective flow and jet suppression. The spectra of particles emitted in gold-gold collisions can be well described by a blastwave model incorporating a kinetic temperature and an expansion velocity. The relative number of various types of particles can be well described by a thermal model using a chemical temperature and a chemical potential. Collective flow manifests itself in terms of azimuthal anisotropies. The original anisotropy in the overlap region of the two colliding nuclei is translated into momentum correlations in the final state. Central collisions of gold nuclei also show strong jet suppression. Jets are created when a quark or a gluon undergoes a hard scattering with another quark or gluon. These highenergy quarks or gluons cannot be observed directly, and the quark or gluon decays into a jet of observable particles in the direction of the original quark or gluon. By comparing gold-gold collisions with deuteron-gold and proton-proton collisions, RHIC experimenters were able to show that the quark-gluon liquid originates with the scattering of quark and gluons.

I am also working on the design and construction of a TPC to carry out studies of the isospin dependence of the nuclear equation of state at NSCL.


A central collision of two gold nuclei at 130 GeV per nucleon pair as observed in the STAR detector at RHIC. The figure is drawn looking down the beam line of RHIC.