  With the QGP opacity computed perturbatively and with the global entropy
constraints imposed by the observed $dN_{ch}/dy\approx1000$, radiative energy
loss alone cannot account for the observed suppression of single non-photonic
electrons. We show that collisional energy loss, which previously has been
neglected, is comparable to radiative loss for both light and heavy jets and
may in fact be the dominant mechanism for bottom quarks. Predictions taking
into account both radiative and collisional losses significantly reduce the
discrepancy with data. In addition to elastic energy loss, it is critical to
include jet path length fluctuations to account for the observed pion
suppression.
