Pseudorapidity and Centrality Dependence of the Collective Flow of Charged Particles in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ Collisions at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$

This paper describes the measurement of collective flow for charged particles in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=130\mathrm{G}\mathrm{e}\mathrm{V}$ using the PHOBOS detector at the Relativistic Heavy Ion Collider (RHIC). The measured azimuthal hit anisotropy is presented over a wide range of pseudorapidity ($-5.0<\eta <5.3$) for the first time at this energy. The result, averaged over momenta and particle species, is observed to reach 7% for peripheral collisions at midrapidity, falling off with centrality and increasing $|\eta |$. These results call into question the common assumption of longitudinal boost invariance over a large region of rapidity in RHIC collisions.

Figure 1

The event distribution as a function of $N_{\mathrm{p}\mathrm{a}\mathrm{r}\mathrm{t}}$ for triggered events (upper curve) and for data accepted for use in the final analysis (lower curve).

Figure 2

Reconstructed event plane angle correlation between subevents $\mathrm{O}\mathrm{C}\mathrm{T}-$ and $\mathrm{O}\mathrm{C}\mathrm{T}+$ as a function of centrality bin. This quantity is directly related to the event plane resolution, as shown in Eq. (5).

Figure 3

Fully corrected measurement of elliptic flow, ${\mathrm{v}}_2$, as a function of the number of participants for $|\eta |<1.0$. The black error bars represent the $1\sigma$ statistical errors and the gray bands give a measure of the systematic error for each point at $\sim 90\%$ confidence level.

Figure 4

Elliptic flow, averaged over centrality, as a function of $\eta$. The graphical representation of the errors is similar to that shown in Fig. 3. The points on the negative side are reflected about $\eta =0$ and shown on the positive side as open circles.