Speakers
Description
We report high-statistics measurements of semi-inclusive distributions of charged jets recoiling from high-$E_{\text{T}}$ direct photon ($\gamma_{\text{dir}}$) and $\pi^{0}$ triggers in $p$+$p$ and central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. In a semi-inclusive approach, event bias is induced solely by the choice of trigger; separately utilizing $\gamma_{\text{dir}}$ and $\pi^{0}$ triggers in this analysis therefore provides direct comparison of jet quenching effects for jet populations with different q/g fractions and different in-medium path length distributions. Jets are reconstructed from charged particles using the anti-$\text{k}_{\text{T}}$ algorithm with jet resolution parameters $R_{\text{jet}} = 0.2$ 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 $p_{\text{T}}$ and large $R_{\text{jet}}$ with well-controlled systematic uncertainties, which are of particular importance in searching for jet scattering effects. We report recoil jet yield and trigger-jet acoplanarity distributions for jets with $p_{\text{T}} > 5$ GeV/$c$. The comparison of recoil yields in Au+Au and $p$+$p$ collisions at fixed $R_{\text{jet}}$ probes energy loss in heavy-ion collisions. Moreover, the comparison of recoil yields for different $R_{\text{jet}}$ in Au+Au and $p$+$p$ collisions probes intra-jet broadening. The modification of trigger-jet acoplanarity distributions in central Au+Au collisions relative to $p$+$p$ collisions highlights the sensitivity of such a measurement to QGP transport parameters. We also search for evidence of large-angle scattering of jets off of quasi-particles in the QGP. The measured recoil yields and acoplanarity distributions are compared to theoretical calculations.
