Centrality and pseudorapidity dependence of elliptic flow for charged hadrons in Au+Au collisions at sqrt(sNN) = 200 GeV

Abstract

This paper describes the measurement of elliptic flow for charged particles in Au+Au collisions at sqrt(sNN)=200 GeV using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal anisotropy is presented over a wide range of pseudorapidity for three broad collision centrality classes for the first time at this energy. Two distinct methods of extracting the flow signal were used in order to reduce systematic uncertainties. The elliptic flow falls sharply with increasing eta at 200 GeV for all the centralities studied, as observed for minimum-bias collisions at sqrt(sNN)=130 GeV.

Figures (5)

• Figure 1: Elliptic flow as a function of pseudorapidity ($v_{2} (\eta)$) for charged hadrons in minimum-bias collisions at $\sqrt{s_{_{NN}}}=130$ GeV (open triangles) phobos130flow and $200$ GeV (closed triangles). One sigma statistical errors are shown as the error bars. Systematic errors (90% C.L.) are shown as gray boxes only for the 200 GeV data.
• Figure 2: Elliptic flow ($v_2(\left| \eta \right|<1)$) as a function of $\langle N_{part} \rangle$ determined by the track-based method (closed circles) and hit-based method (closed triangles) for Au+Au collisions at $200$ GeV. The open triangles are the results from Au+Au collisions at 130 GeV. One sigma statistical errors are shown as the error bars (within the points for the track-based method); gray and open boxes show systematic uncertainties (90% C.L.) for the 200-GeV results from the hit-based and track-based methods, respectively. The line shows a calculation from hydrodynamics HydroLineModel at $\sqrt{s_{_{NN}}}=200$ GeV.
• Figure 3: Elliptic flow as a function of transverse momentum ($v_{2}(p_{T})$) for charged hadrons with $0<\eta<1.5$ for the most central $50\%$ of the 200 GeV Au+Au inelastic cross section. The one sigma statistical errors are shown as the error bars. The gray boxes represent the systematic errors (90% C.L.). The data points are located at the average $p_{T}$ position within a $p_{T}$ bin whose size is given by the horizontal error bars. The curve shows a calculation from hydrodynamics HydroLineModel.
• Figure 4: Elliptic flow as a function of pseudorapidity ($v_{2}(\eta)$) for charged hadrons from 200-GeV Au+Au collisions for the three different centrality classes described in the text, ranging from peripheral to central ($25-50\%$, $15-25\%$, $3-15\%$) from top to bottom. The triangles are the results from the hit-based method, and the circles are from the track-based method. The open circles are the track-based results reflected about mid-rapidity. One sigma statistical errors are shown as the error bars (within the points for the track-based method); the gray and open boxes show the systematic uncertainties (90% C.L.) for the hit-based and track-based methods, respectively.
• Figure 5: Elliptic flow as a function of pseudorapidity ($v_{2}(\eta)$) from 200-GeV Au+Au collisions for the three centrality bins ($3-15\%$ circles, $15-25\%$ triangles, $25-50\%$ squares). Data for $\eta>0$ are determined by reflecting the hit-based results about mid-rapidity and then combining them with the track-based results and are shown with the corresponding combined 90% C.L. statistical and systematic uncertainties. The same data are reflected around $\eta = 0$ and shown as open symbols. In the range where the methods overlap, the insert shows the ratio of the peripheral to central results, with the appropriate 90% C.L. combined uncertainties.