  We point out that events associated with large $E_T$ direct photons in
high-energy heavy-ion collisions can be used to study jet energy loss in dense
matter. In such events, the $p_T$ spectrum of charged hadrons from jet
fragmentation in the opposite direction of the tagged photon is estimated to be
well above the background which can be reliably subtracted at moderately large
$p_T$. We demonstrate that comparison between the extracted fragmentation
function in $AA$ and $pp$ collisions can be used to determine the jet energy
loss and the interaction mean-free-path in the dense matter produced in
high-energy heavy-ion collisions.
