Semi-inclusive direct photon+jet and ${\pi }^0$+jet correlations measured in $p+p$ and central Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV

Abstract

The STAR experiment at RHIC reports new measurements of jet quenching based on the semi-inclusive distribution of charged-particle jets recoiling from direct photon (${\gamma }_{\mathrm{dir}}$) and neutral pion (${\pi }^0$) triggers in pp and central Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV, for triggers in the range $9<E_{\mathrm{T}}^{\mathrm{trig}}<20$ GeV. The datasets have integrated luminosities of 3.9${\mathrm{nb}}^{-1}$ for Au+Au and 23${\mathrm{pb}}^{-1}$ for pp collisions. Jets are reconstructed using the anti-$k_{\mathrm{T}}$ algorithm with resolution parameters $R$=0.2 and 0.5. The large uncorrelated jet background in central Au+Au collisions is corrected using a mixed-event approach, which enables precise charged-particle jet measurements at low transverse momentum $p_{\mathrm{T},\mathrm{jet}}^{\mathrm{ch}}$ and large $R$. Recoil-jet distributions are reported in the range $p_{\mathrm{T},\mathrm{jet}}^{\mathrm{ch}}<25$ \gev. Comparison of the distributions measured in pp and Au+Au collisions reveals strong medium-induced jet yield suppression for $R=0.2$, with markedly less suppression for $R=0.5$. Comparison is also made to theoretical models incorporating jet quenching. These data provide new insight into the mechanisms underlying jet quenching and the angular dependence of medium-induced jet-energy transport, and provide new constraints on modelling such effects.

Comments: Accepted by PRC along with companion PRL paper arXiv:2309.00156