On the nuclear modification factor at RHIC and LHC

We show that pQCD factorization incorporated with pre-hadronization energy-loss effect naturally leads to flatness of the nuclear modification factor image for produced hadrons at high transverse momentum image. We consider two possible scenarios for the pre-hadronization: In scenario 1, the produced gluon propagates through dense QCD medium and loses energy. In scenario 2, all gluons first decay to quark–antiquark pairs and then each pair loses energy as propagating through the medium. We show that the estimates of the energy-loss in these two different models lead to very close values and is able to explain the suppression of high-image hadrons in nucleus–nucleus collisions at RHIC. We show that the onset of the flatness of image for the produced hadron in central collisions at midrapidity is about image and 25 GeV at RHIC and the LHC energies, respectively. We show that the smallness (image ) and the high-image flatness of image obtained from the image factorization supplemented with the Balitsky–Kovchegov (BK) equation is rather generic and it does not strongly depend on the details of the BK solutions. We show that energy-loss effect reduces the nuclear modification factor obtained from the image factorization about 30–50% at moderate image.