Measurement of in-medium jet modification using direct photon+jet and $\pi^{0}$+jet correlations in $p+p$ and central Au+Au collisions at $\sqrt{s_{\rm NN}} = 200$ GeV

TL;DR

This study measures how jets are modified in a hot medium created in heavy-ion collisions by analyzing correlations with direct photons and neutral pions, revealing the angular dependence of jet quenching effects.

Contribution

It provides new experimental data on jet suppression at different angular scales in Au+Au collisions, challenging existing jet quenching models.

Findings

Jet yield suppression is greater for smaller jet resolution parameter R=0.2.

Jet energy redistribution occurs over a broader angular range than predicted.

Model calculations do not fully match the observed suppression patterns.

Abstract

The STAR Collaboration presents measurements of the semi-inclusive distribution of charged-particle jets recoiling from energetic direct-photon ($\gamma_{\rm dir}$) and neutral-pion ($\pi^{0}$) triggers in p+p and central Au+Au collisions at $\sqrt{s_\mathrm{NN}}$ GeV over a broad kinematic range, for jet resolution parameters $R$=0.2 and 0.5. Medium-induced jet yield suppression is observed to be larger for $R$=0.2 than for 0.5, reflecting the angular range of jet energy redistribution due to quenching. The predictions of model calculations incorporating jet quenching are not fully consistent with the observations. These results provide new insight into the physical origins of jet quenching.