Solving the qˆ puzzle with x and scale dependence

Abstract We present here a possible resolution of the jet quenching parameter q ˆ puzzle by exploring the momentum fraction x and scale Q 2 dependence of q ˆ , in addition to temperature dependence. We explore the momentum broadening of the jet due to Glauber gluon exchange with the quark-gluon plasma (QGP). This has led us to define the momentum fraction x for the partons in the QGP. We also show here, for the first time, possible forms of the parton distribution function (PDF) of the QGP. The QGP-PDF as input in q ˆ has been used to fit the PHENIX and CMS data simultaneously. We observe that the scale evolution of the QGP-PDF and the energy of the jet are the missing ingredients responsible for the enhancement of q ˆ at the same temperature in RHIC collisions compared to LHC collisions.