Suppression of away-side jet fragments with respect to the reaction plane in Au+Au collisions at sqrt(s_NN) = 200 GeV

TL;DR

This study investigates how the suppression of away-side jet fragments in Au+Au collisions at 200 GeV depends on their orientation relative to the reaction plane, revealing insights into parton energy loss mechanisms in hot dense matter.

Contribution

It provides new experimental data on jet suppression dependence on reaction-plane orientation at high transverse momentum in heavy-ion collisions.

Findings

Out-of-plane triggers produce significantly fewer away-side pairs than in-plane triggers.

Near-side jet fragments show no suppression or dependence on trigger orientation.

Results support models of increased away-side energy loss due to longer medium traversal.

Abstract

Pair correlations between large transverse momentum neutral pion triggers (p_T=4--7 GeV/c) and charged hadron partners (p_T=3--7 GeV/c) in central (0--20%) and midcentral (20--60%) Au+Au collisions are presented as a function of trigger orientation with respect to the reaction plane. The particles are at larger momentum than where jet shape modifications have been observed, and the correlations are sensitive to the energy loss of partons traveling through hot dense matter. An out-of-plane trigger particle produces only 26+/-20% of the away-side pairs that are observed opposite of an in-plane trigger particle. In contrast, near-side jet fragments are consistent with no suppression or dependence on trigger orientation with respect to the reaction plane. These observations are qualitatively consistent with a picture of little near-side parton energy loss either due to surface bias or fluctuations and increased away-side parton energy loss due to a long path through the medium. The away-side suppression as a function of reaction-plane angle is shown to be sensitive to both the energy loss mechanism in and the space-time evolution of heavy-ion collisions.