Jet-mass Dependence of the in-Medium Shower Modification
  While the modification of jets by a medium as created in ultrarelativistic heavy-ion collisions is often thought of as a phenomenon affecting a hard near on-shell parton and hence treated as partonic energy loss, a more realistic view is to think of the medium effect as a relatively small correction to the Quantum Chromodynamics (QCD) vacuum radiation pattern which reduces the initial high virtuality of hard partons and leads to the development of a shower. The uncertainty relation can be used to argue that a significant part of this shower is developed even before a medium can be formed. The initial virtuality of a shower-initiating parton is reflected in the final state in the measured invariant mass of a jet - high mass jets are characterized by more branchings, higher multiplicity and a wider angular structure. Since most of this structure is determined before the medium affects the jet, selecting a particular jet mass range strongly biases the partonic configuration that enters the medium, and thus the medium is expected to modify high mass jets more strongly than low mass jets. In this work, this scenario is explored using the in-medium shower evolution code YaJEM and a possible strategy for a measurement is suggested. 
Thorsten Renk
hep-ph