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

TL;DR

This study measures two-dimensional autocorrelations of charged hadrons in gold-gold collisions at 62 and 200 GeV, revealing anomalous variations in minijet correlations linked to collision centrality and energy.

Contribution

It uncovers a sudden increase in minijet correlation amplitude and width at a specific centrality, indicating new behavior in parton scattering in heavy-ion collisions.

Findings

Excess of minijet correlations in central collisions beyond binary-collision expectations.

Sudden increase in minijet peak amplitude and width at a specific centrality.

Possible scaling of transition point with particle density.

Abstract

We have measured 2D autocorrelations for all charged hadrons in STAR with $p_{t}$ $>$ 0.15 GeV/c and $| \eta |$ $<$ 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 $\eta$ 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.