Measurement of medium-induced modification of jet yield and acoplanarity using semi-inclusive $\gamma_{\text{dir}}$+jet and $\pi^{0}$+jet distributions in $p$+$p$ and central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV by STAR

TL;DR

This paper reports on measurements of jet modifications in heavy-ion collisions, revealing medium-induced suppression and broadening effects through semi-inclusive gamma and pi0 triggered jet distributions at RHIC.

Contribution

It provides the first detailed study of jet suppression and acoplanarity dependence on jet size and trigger energy in Au+Au collisions at 200 GeV.

Findings

Jet suppression increases with larger jet radius.

Intra-jet broadening observed in Au+Au compared to p+p.

Enhanced acoplanarity indicates medium-induced scattering.

Abstract

The STAR collaboration presents measurements of semi-inclusive distributions of charged jets recoiling from high transverse energy ($E_{\text{T}}$) direct photon and $\pi^{0}$ triggers in $p$+$p$ and central Au+Au collisions at $\sqrt{s_{\text{NN}}} = 200$ GeV. Jets are reconstructed from charged particles using the anti-$k_{\text{T}}$ algorithm with jet resolution parameters $R = 0.2$ and 0.5. The large uncorrelated background in central Au+Au collisions is corrected using a mixed-event technique. This enables a jet measurement extending to low transverse momentum and large $R$ with well-controlled systematic uncertainties. We present measurements of the jet $R$ dependence of suppression, intra-jet broadening, and acoplanarity of $\pi^{0}$+jet and $\gamma_{\text{dir}}$+jet for trigger $E_{\text{T}}$ ($E_{\text{T}}^{\text{trig}}$) between $9 - 20$ GeV.