Jet cross sections and jet shapes: from hadrons to nuclei

Abstract:

For jets, with great power comes great opportunity. The unprecedented
center of mass energies available at the LHC open new windows on the
QGP: we demonstrate that jet shape and jet cross section measurements
become feasible as a new, differential and accurate test of the
underlying  QCD theory.  We present a first step in understanding
these shapes and  cross sections
in heavy ion reactions. Our approach allows for detailed simulations of
the experimental acceptance/cuts that help isolate jets in such high-
multiplicity environment. It is demonstrated for the first time that
the pattern of stimulated gluon emission can be correlated with a
variable quenching of the jet rates
and provide an approximately model-independent approach to determining
the characteristics of the medium-induced bremsstrahlung spectrum.
The largest difference between the jet shape in vacuum and the total
in-medium jet shape is manifest in the periphery of the jet cone and
for small cone radii. The enhancement of the mean relative
jet radius due to the QGP effect is found to be rather modest.