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star physics results: Spectra and yields

Note: Click on a figure for a larger version.


Figure. The pbar/p ratio from Au+Au collisions at sqrt(snn) = 130 GeV (a) as a function of pT within the rapidity range 0.3 < |y| < 0.4; (b) as a function of y within 0.6 < pT < 0.8 GeV/c; (c) as a function of collision centrality within |y| < 0.3 and 0.6 < pT < 0.8 GeV/c from the reanalysis (solid circles) compared to the previous publication (open circles). Panels (a) and (b) show results for minimum bias collisions.

Midrapidity Antiproton-to-Proton Ratio from Au+Au Collisions at sqrt(snn) = 130 GeV

The primary goal of the heavy-ion collision program at the Relativistic Heavy Ion Collider (RHIC) is to create and study a novel state of matter constituted of deconfined quarks and gluons, named quark-gluon plasma. The formation of such a deconfined state depends on the initial conditions of the matter created at the early stage of heavy-ion collisions. One of the important observables is the baryon number transport (or stopping) that is achieved mostly at the early stage. The degree of baryon stopping affects the overall dynamical evolution of these collisions, and the measurement of the antiproton-to-proton (pbar/p) yields may provide information on the baryon transport.

The pbar/p ratio at midrapidity was measured by STAR in Au+Au collisions at sqrt(snn) = 130 GeV. The ratio is independent of tranverse momentum (pT) and rapidity (y) within |y| < 0.5 and 0.4 < pT < 1.0 GeV/c (see panels (a) and (b) in the Figure). In the same kinematic range, the average pbar/p ratio is 0.73 +- 0.003(stat) +- 0.05(syst) for minimum bias collisions. In the centrality interval measured, no strong centrality dependence is observed (see panel (c) in the Figure). The measured pbar/p ratio indicates that even though the antibaryon-baryon (pbar-p) pair production becomes important at midrapidity, a significant excess of baryons over anti-baryons is still present in heavy-ion collisions at RHIC. The comparison of the STAR measurement at RHIC to heavy-ion results at lower energies (AGS and SPS) indicate that the midrapidity pbar/p ratio in heavy-ion collisions increases significantly with collision energy.

Related STAR papers

Midrapidity Antiproton-to-Proton Ratio from Au+Au sqrt(snn) = 130 GeV
Phys. Rev. Lett. 86 (2001) 4778
e-Print Archives (nucl-ex/0104022): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

Erratum: Midrapidity Antiproton-to-Proton Ratio from Au+Au sqrt(snn) = 130 GeV [Phys. Rev. Lett. 86 (2001) 4778]
Phys. Rev. Lett. 90 (2003) 119903(E)
Journal article: Phys. Rev. Lett. server


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