  One of the most active areas of investigation in relativistic heavy-ion
collisions is the study of the jet quenching phenomenon whereby hard partons
lose their energy as they traverse the hot, dense matter created in such
collisions. Strong parton energy loss has been observed in central
nucleus-nucleus collisions as evidenced by the a large suppression of the yield
of high pT hadrons as compared to the expected yield based on measurements in
p+p collisions. Moreover, measurements of back-to-back correlations of charged
hadrons suggest that jet shapes are strongly modified modified by the medium.
The quantitative interpretation of single and di-hadron measurements is,
however, complicated by the fact that the initial parton energy is unknown. A
more informative measurement would be one in which the initial parton energy is
known, allowing the determination of the fragmentation function, which may be
effectively modified from its vacuum form by the presence of the medium. Two
measurements in which the initial parton energy may be estimated are discussed
in these proceedings: jet reconstruction and two- particle correlations using
direct photons. Jet reconstruction in nuclear collisions is challenging due to
the large background of soft particles, fluctuations of which give rise to fake
jets. Direct photons can be used to estimate the initial parton energy of the
recoil jet without recourse to jet reconstruction algorithms. However, such
studies suffer from a smaller rate and the direct photon signal must be
disentangled from a large background of decay photons. We present jet
reconstruction results which use an algorithm suitable for a high multiplicity
environment. We also present results of two-particle correlations using direct
photons. These results are discussed in the context of medium modification to
the fragmentation function.
