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 ($\gamma_{\rm dir}$) and neutral pion ($\pi^{0}$) triggers in pp and central Au+Au collisions at $\sqrt{s_{\rm NN}}=200$ GeV, for triggers in the range $9<E_{\rm T}^{\rm trig}<20$ GeV. The datasets have integrated luminosities of 3.9$ {\rm nb}^{-1}$ for Au+Au and 23$ {\rm pb}^{-1}$ for pp collisions. Jets are reconstructed using the anti-$k_{\rm T}$ 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 $p_{\rm T,jet}^{\rm ch}$ and large $R$. Recoil-jet distributions are reported in the range $p_{\rm T,jet}^{\rm ch}<25$\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.
Rho distribution of SE recoil jet R=0.5 for AuAu 0-15% at sqrt{s_{NN}}=200 GeV from gamma_{rich}+jet event sample.
Rho distribution of ME recoil jet R=0.5 for AuAu 0-15% at sqrt{s_{NN}}=200 GeV from MB event sample.
Rho distribution of ME-30MeV recoil jet R=0.5 for AuAu 0-15% at sqrt{s_{NN}}=200 GeV from MB event sample.
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