  Hard QCD processes in ultrarelativistic heavy-ion collisions become
increasingly relevant and they can be used as probes of the dense matter formed
during the violent scatterings. We will discuss how one can use these hard
probes to study the properties of the dense matter and the associated
phenomenologies. In particular, we study the effect of jet quenching due to
medium-induced energy loss on inclusive particle $p_T$ distributions and
investigate how one can improve the measurement of parton energy loss in direct
photon events
