Eccentricity fluctuations and its possible effect on elliptic flow measurements

Abstract

The elliptic flow measured at RHIC has been interpreted as a signature for strong partonic interactions early in the collision and as an indication of a well developed quark-gluon plasma phase. The measured values of elliptic flow, using methods based on multi-particle correlations, are affected by fluctuations in the magnitude of the elliptic flow. In this Letter, using a Monte Carlo Glauber calculation, we estimate what the possible effect of spatial eccentricity fluctuations is on the determination of elliptic flow.

Figures (4)

• Figure 1: Schematic view of a nucleus-nucleus collision in the transverse plane.
• Figure 2: a) Contour plot of the calculated eccentricity in a Monte Carlo Glauber model versus the impact parameter, $b$, in Au+Au collisions. The mean value of the eccentricity is indicated by the dashed curve. b) The mean eccentricity $\langle \epsilon \rangle$ (dashed curve) and the corresponding $\langle \epsilon^{n} \rangle^{1/n}$ for $n = 2$, 4 and 6 (points) versus impact parameter $b$.
• Figure 3: Eccentricity cumulants calculated for Au+Au collisions in a Monte Carlo Glauber model compared to $\langle \epsilon \rangle$ as a function of centrality (from left to right is from central to peripheral collisions, respectively). The symbols are the Monte Carlo Glauber results using nucleons, the lines are for constituent quarks (see text).
• Figure 4: a) Comparison of the calculated $\epsilon\{4\}/\epsilon\{2\}$ for both the nucleon (solid line) and quark (dashed line) MCG to the STAR measurements STAR_flowPRC. b) Non-flow or fluctuation contribution to the azimuthal correlations (see text).