  The first evidence of jet quenching was observed at RHIC via suppression of
single high $p_T$ hadron $R_{AA}$ and the disappearance of the away-side jet
peak in two-particle correlations. Since then, hadron $R_{AA}$ and two-particle
correlations continue to be useful probes of the QGP in heavy ion collisions,
since the particles involved are fragments of the jets produced in the initial
hard scattering. PHENIX recently improved the width measurements extracted from
$\pi^0$-hadron correlations after removing the higher order flow terms in the
underlying event subtraction. Measurements of the away-side jet correlated with
high $p_T$ neutral pions show an increase in low momentum particle production
at wide angles consistent with theoretical expectations for energy loss. The
system size dependence of energy loss is further investigated at PHENIX by
measuring the absolute yield and $R_{AA}$ for various hadron species at high
$p_T$ in several collision systems including $U+U$ and $Cu+Au$. These
proceedings will present the newest PHENIX $R_{AA}$ and two-particle
correlation measurements and their role in our understanding of jet quenching
and medium response in heavy ion collisions
