  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
$p+p$ and central Au+Au collisions at $\sqrt{s_\mathrm{NN}} = 200$ GeV, for
triggers in the range $9< E_{T}^{\rm trig}<20$ GeV. The datasets have
integrated luminosities of 3.9 $\rm nb^{-1}$ for Au+Au and 23 $\rm pb^{-1}$ for
$p+p$ 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 $p+p$ and Au+Au collisions reveals
strong medium-induced jet yield suppression for $R=0.2$, with markedly less
suppression for $R=0.5$. These data provide new insight into the mechanisms
underlying jet quenching, and the angular dependence of medium-induced
jet-energy transport.
