Eur. Phys. J. A (2010) 45: 353-356
https://doi.org/10.1140/epja/i2010-11013-2

Regular Article - Theoretical Physics

Correlations among elliptic flow parameter, impact parameter, and multiplicity

¹ Institute of Particle Physics, Huazhong Normal University, 430082, Wuhan, China
² Institute of Physics and Technology, University of Bergen, Allegaten 55, 5007, Bergen, Norway
³ China Institute of Atomic Energy, P. O. Box 275 (18), 102413, Beijing, China
⁴ CCAST (World Lab.), P. O. Box 8730, 100080, Beijing, China
⁵ Frankfurt Institute for Advanced Studies, Johann Wolfgang Goethe University, Ruth-Moufang-Str. 1, 60438, Frankfurt am Main, Germany

^* e-mail: zhoudm@phy.ccnu.edu.cn

Received: 5 May 2010
Revised: 14 June 2010
Accepted: 12 July 2010
Published online: 30 July 2010

Abstract

The elliptic flow parameter, v₂, in the Fourier expansion of the event-by-event charged-particle multiplicity azimuthal distribution in the momentum space is studied by taking into account the multiplicity fluctuations. The correlations among measurable variables of v₂, charged multiplicity, and impact parameter are investigated using a multiple phase transport model with string melting. It turned out that the charged multiplicity and impact parameter are negatively correlated. This correlation results in the peak structure in v₂ as a function of the participant nucleon number (charged multiplicity, impact parameter) measured in RHIC experiments. It is suggested that v₂ calculated in the event-wise average is about 20% larger than in the particle-wise average, so event-wise average should be used in the theoretical calculations.