  Medium modification of jet fragmentation function due to multiple scattering
and induced gluon radiation leads directly to jet quenching or suppression of
leading particle distribution from jet fragmentation. One can extract an
effective total parton energy loss which can be related to the total transverse
momentum broadening. For an expanding medium, both are shown to be sensitive to
the initial parton density and formation time. Therefore, one can extract the
initial parton density and formation time from simultaneous measurements of
parton energy loss and transverse momentum broadening. Implication of the
recent experimental data on effects of detailed balance in parton energy loss
is also discussed.
