Centrality Dependence of ∆η −∆φ Correlations in Heavy Ion Collisions

In these proceedings, a measurement of two-particle correlations with a high transverse momentum trigger particle (p T > 2.5 GeV/c) is presented for Au+Au collisions at √ sNN =200 GeV over the uniquely broad longitudinal acceptance of the PHOBOS detector (−4 < ∆η < 2). As in p+p collisions, the near-side is characterized by a peak of correlated partners at small angle relative to the trigger. However, in central Au+Au collisions an additional correlation extended in ∆η and known as the ‘ridge’ is found to reach at least |∆η| ≈ 4. The ridge yield is largely independent of ∆η over the measured range, and it decreases towards more peripheral collisions. For the chosen p T cut of 2.5 GeV/c, the ridge yield is consistent with zero for events with less than roughly 100 participating nucleons.