Anomalous centrality variation of minijet angular correlations in Au-Au collisions at 62 and 200 GeV from STAR

摘要

We have measured 2D autocorrelations for all charged hadrons in STAR with p(t) > 0.15 GeV/c and vertical bar eta vertical bar < 1 from Au+Au collisions at 62 and 200 GeV. The correlation structure is dominated by a peak centered at zero relative opening angles on eta and phi which we hypothesize is caused by minimum-bias jets (minijets). We observe a large excess of minijet correlations in more-central Au -Au collisions relative to binary-collision scaling (more correlated pairs than expected from surface emission or even volume emission). We also observe a sudden increase of the minijet peak amplitude and. width relative to binary-collision scaling of scattered partons which occurs at an energy-dependent centrality point. There is a possible scaling of the transition point with transverse particle density. The large minijet correlations bring into question the degree of thermalization in RHIC collisions.