/ Experiment-Nucl nucl-ex/0701010

Mass, quark-number, and sqrt s(NN) dependence of the second and fourth flow harmonics in ultra-relativistic nucleus-nucleus collisions

Abelev, B.I. ; Aggarwal, M.M. ; Ahammed, Z. ; Anderson, B.D. ; Arkhipkin, D. ; Averichev, G.S. ; Bai, Y. ; Balewski, J. ; Barannikova, O. ; Barnby, L.S. ; Baudot, J. ; Baumgart, S. ; Bekele, S. ; Belaga, V.V. ; Bellingeri-Laurikainen, A. ; Bellwied, R. ; Benedosso, F. ; Betts, R.R. ; Bhardwaj, S. ; Bhasin, A. ; Bhati, A.K. ; Bichsel, H. ; Bielcik, J. ; Bielcikova, J. ; Bland, L.C.

Published in: Phys.Rev.
Year: 2007
Vol.: C75
Page No: 054906
Pages: 12

Abstract: We present STAR measurements of the azimuthal anisotropy parameter $v_2$ for pions, kaons, protons, $\Lambda$, $\bar{\Lambda}$, $\Xi+\bar{\Xi}$, and $\Omega + \bar{\Omega}$, along with $v_4$ for pions, kaons, protons, and $\Lambda + \bar{\Lambda}$ at mid-rapidity for Au+Au collisions at $\sqrt{s_{_{NN}}}=62.4$ and 200 GeV. The $v_2(p_T)$ values for all hadron species at 62.4 GeV are similar to those observed in 130 and 200 GeV collisions. For observed kinematic ranges, $v_2$ values at 62.4, 130, and 200 GeV are as little as 10%--15% larger than those in Pb+Pb collisions at $\sqrt{s_{_{NN}}}=17.3$ GeV. At intermediate transverse momentum ($p_T$ from 1.5--5 GeV/c), the 62.4 GeV $v_2(p_T)$ and $v_4(p_T)$ values are consistent with the quark-number scaling first observed at 200 GeV. A four-particle cumulant analysis is used to assess the non-flow contributions to pions and protons and some indications are found for a smaller non-flow contribution to protons than pions. Baryon $v_2$ is larger than anti-baryon $v_2$ at 62.4 and 200 GeV perhaps indicating either that the initial spatial net-baryon distribution is anisotropic, that the mechanism leading to transport of baryon number from beam- to mid-rapidity enhances $v_2$, or that anti-baryon and baryon annihilation is larger in the in-plane direction.

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