Forward- and Mid-Rapidity Jet-like correlations

TL;DR

This paper presents preliminary measurements of azimuthal correlations between forward and mid-rapidity hadrons in various collision systems at 200 GeV, exploring gluon distributions and jet quenching effects.

Contribution

It provides new experimental data on forward-mid rapidity correlations in pp, d+Au, and Au+Au collisions, offering insights into small-x gluon saturation and quark jet energy loss.

Findings

Evidence for gluon saturation effects in d+Au collisions.

Indications of quark-jet modification in Au+Au collisions.

Differences in correlations between d-side and Au-side in d+Au collisions.

Abstract

Mid-rapidity azimuthal correlations probe di-jets originating mainly from gluon-gluon hard-scattering. Measurements of such correlations have revealed significant (gluon-)jet modification in central Au+Au collisions. Azimuthal correlations of hadrons at forward rapidity with a mid-rapidity high-$\pt$ hadron, on the other hand, probe asymmetric partonic scatterings involving large-x quarks and small-x gluons. We present preliminary results from STAR on correlations of charged hadrons at forward rapidity in the forward TPCs ($2.7<|\eta|<3.9$, $\pt<2$ GeV/$c$) with high-$\pt$ charged hadrons at mid-rapidity from the main TPC ($|\eta|<1$, $\pt>3$ GeV/$c$) in $pp$, d+Au, and Au+Au collisions at $\snn=200$ GeV. The implications of the results for small-x gluon distributions (Color Glass Condensate formation) and the energy loss of quark jets at forward rapidity in nuclear medium are discussed. %Their measurements in d+Au collisions, separately at the d-side and the Au-side, may be sensitive to Color Glass Condensate in the Au-nucleus. Their measurements in Au+Au collisions may probe quark-jet modification in nuclear medium.