Elliptic flow in Au+Au collisions at sqrt(s_NN) = 130 GeV

Abstract

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at sqrt(s_NN)=130 GeV using the STAR TPC at RHIC. The elliptic flow signal, v_2, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

Figures (4)

• Figure 1: The primary track multiplicity distribution as a function of the number of tracks normalized by the maximum observed number of tracks. The eight centrality regions used in this analysis are shown. The integral under the curve is 1.0 and the cumulative fraction corresponding to the lower edge of each centrality bin is also indicated in percent.
• Figure 2: Correlation between the event plane angles determined for two independent subevents. The upper set of data is for the second harmonic and the lower set is $\langle \cos(\Psi^a-\Psi^b)\rangle$ for the first harmonic. The points are positioned at the values of mean $n_{ch}/n_{max}$ corresponding to each of the centrality bins in Fig.\ref{['mult']}. The horizontal bars show the widths of the bins.
• Figure 3: Elliptic flow (solid points) as a function of centrality defined as $n_{ch}/n_{max}$. The open rectangles show a range of values expected for $v_2$ in the hydrodynamic limit, scaled from $\epsilon$, the initial space eccentricity of the overlap region. The lower edges correspond to $\epsilon$ multiplied by 0.19 and the upper edges to $\epsilon$ multiplied by 0.25.
• Figure 4: Elliptic flow as a function of transverse momentum for minimum bias events.