Midrapidity Antiproton-to-Proton Ratio fromAu+AuCollisions atsNN

Abstract

We report results on the ratio of midrapidity antiproton-to-proton yields in Au+Au collisions at sqrt[s(NN)] = 130 GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of /y/<0.5 and 0.4<p(t)<1.0 GeV/c, the ratio is essentially independent of either transverse momentum or rapidity, with an average of 0.65+/-0.01((stat))+/-0.07((syst)) for minimum bias collisions. Within errors, no strong centrality dependence is observed. The results indicate that at this RHIC energy, although the p-p pair production becomes important at midrapidity, a significant excess of baryons over antibaryons is still present.

Partonic Effects in Heavy Ion Collisions at RHIC

“…The measured total charged particle multiplicities at mid-pseudorapidity at both energies are well reproduced by our model. Also, thep/p ratio predicted by the AMPT model is consistent with that measured in experiments [ 25]. The transverse momentum spectra of pions, kaons, and protons in Au+Au collisions at √ s = 130A GeV are shown in the right panel of Fig.…”

MidrapidityΛandΛ¯Production inAu+AAdler1, Ahammed2, Allgower3 et al. 2002Phys. Rev. Lett.Self Cite1621120View full textAdd to dashboardCite

“…The first results from the Relativistic Heavy Ion Collider (RHIC) have shown that the large charged particle multiplicity, measured in Au+Au collisions at √ s N N = 130 GeV, corresponds to an energy density significantly higher than that previously achieved in heavy ion collisions [2,3,4]. In addition, the anti-proton to proton ratio at mid-rapidity has been measured to be in the range 0.6-0.7 [5,6,7], which is indicative of particle production from a low net baryon density regime. Thus the global characteristics of nucleus-nucleus collisions at RHIC are the formation of a high energy density and low net baryon density region at mid-rapidity.…”

What are we learning from RHIC?

“…and antibaryons is still sizable, withp/p ratio about 0.65 [ 28]. This signals the diffusion of baryon number to quite small values of Bjorken x ∼ 10 −2 .…”