  In 1998, at the 4th QCD workshop, Rolf Baier asked me whether jets could be
measured in Au+Au collisions because he had a prediction of a QCD medium-effect
(energy loss via soft gluon radiation induced by multiple scattering) on
color-charged partons traversing a hot-dense-medium composed of screened
color-charges. I reviewed the possibilities in a talk explaining that there was
a general consensus that for Au+Au central collisions at $\sqrt{s_{NN}}=200$
GeV, leading particles are the only way to find jets because of the large
particle density. The good news was that hard-scattering in p-p collisions was
originally observed by the method of leading particles and that these
techniques could be used to study hard-scattering and jets in Au+Au collisions.
Notably, I described ``How everything you want to know about jets can be found
using 2-particle correlations''. In fact, the predicted ``jet quenching'' and
other new phenomena were discovered by this method. However, this past year, I
had to soften the statement to {\em almost everything} because we found by
explicit calculation in PHENIX that the away-side two-particle correlation
$p_{T_a}$ spectrum from a $\pi^0$ trigger with $p_{T_t}$ is not sensitive to
the fragmentation function--overturning a belief dating from the seminal paper
of Feynman, Field and Fox in 1977. A new formula was derived which showed that
the shape of the $p_{T_a}$ spectrum depends only on the power $n$ of the parton
invariant cross section so that NLO pQCD calculations of the two particle
away-side correlations are, in fact, less sensitive to the shape of the
fragmentation function than calculations of the inclusive $\pi^0$ cross
section.
