Nuclear Physics Seminar

The freeze-out of an extended, strongly-interacting system created in a relativistic heavy ion
collision near the QCD critical endpoint could create observable non-statistical fluctuations
in net charge, strangeness and baryon number. We present results for K/pi [(K++K−)/(pi++
pi−)] and p/_ [(p+p)/(pi+ +pi−)] fluctuations from central Au+Au collisions at sqrt(sNN)= 20,
62.4, 130, and 200 GeV in terms of the variable nudyn. We compare these results with recent
data from NA49 [1] for central Pb-Pb collisions at sqrt(sNN)= 6.3, 7.6, 8.7, 12.3, and 17.3 GeV.
The energy dependence of the present data for central collisions extends smoothly from the
NA49 measurements. We present the centrality dependence of K/pi and p/pi fluctuations
from Au+Au collisions at sqrt(sNN)= 62.4 and 200 GeV in terms of the variable nudyn,K_ . To
minimize contributions from background protons, we restrict our measurements for p and
p to the transverse momentum range 0.4 < pt < 1.0 GeV/c. We present results for K/pi
and p/pi fluctuations separated by sign (K+/pi+, K−/pi−, K−/pi+, K+/pi−, p/pi+, p/pi−,
p/pi+, and p/pi−) as a function of centrality. In addition, we present results for net charge
fluctuations (pi+/pi−), net strangeness fluctuations (K+/K−), and net baryon fluctuations
(p/p). We compare our results with the predictions of the HIJING and UrQMD models.

References:
1. NA49 Collaboration, arXiv:0808.1237v2 [nucl-ex] (2008)