Elastic energy loss in an expanding QGP

Abstract

The discovery of the jet quenching in central Au + Au collisions at the Relativistic Heavy-ion Collider (RHIC) has provided clear evidence for the formation of strongly interacting dense matter. It has been predicted to occur due to the energy loss of high energy partons that propagate through the quark gluon plasma. Since the medium is not static and it cools while expands, the strong coupling is not fixed, running with the evolution of the system. In this work, we present an investigation of the dependence on the value of the strong coupling in the parton energy loss due to elastic scatterings in a parton plasma. We analyze different prescriptions for the QCD coupling and calculate the energy and length dependence of the fractional energy loss. Moreover, the quenching factor for light and heavy quarks is estimated. We found that the predicted enhancement of heavy to light hadrons (D/π) ratio is strongly dependent on the running of the QCD coupling constant.Keywords: Quark Gluon Plasma; Elastic energy loss; Running coupling constant In the last years, the understanding of the partonic energy loss has been extensively developed. It was provocated by the expectation of the Quark Gluon Plasma (QGP) formation in the early stages of the collision. The discovery of jet quenching in central Au+Au collisions at RHIC has provided evidences for the formation of this strongly interacting dense matter. Basically, high parton density produced in heavy ion collisions could induce a large amount of energy loss for hard partons produced in the initial stage of the collision during its propagation through the fireball, due to their interactions with the medium.The total energy loss of a particle in a medium can be decomposed into an elastic and a radiative contribution. At large energies one expects that radiative energy loss becomes much larger than the collisional one, as in the electromagnetic case. However, since at lower energies the elastic and radiative processes can contribute equally, for small values of the parton energy the collisional one can dominate. So, an open question is to quantify the contribution of each process in the RHIC kinematical region. Recent studies of elastic mechanism contributions to energy loss [1][2][3][4] have indicate that, for RHIC regimes, it is far from clear that radiative energy loss dominates over elastic one.Besides, we have to consider that the medium properties and interactions change with time (For a discussion of the medium evolution see, e.g. Refs. [5,6]), since in nucleusnucleus collisions, at collider energies, the produced hard partons propagate through a rapidly expanding medium. The scenario assumed here consider that the interactions in the plasma of quarks and gluons get stronger with the time because the average parton energies drop due to the expansion of the system [7,8]. The basic idea comes from the feature that the QGP is not a static medium, but it is cooling while partons propagate through. We assume that the temperature is the dominant scale and consequently will c...

Evolution of heavy quark distribution function on quark-gluon plasma: Using the Iterative Laplace Transform Method

“…The collisional energy loss of a heavy quark with energy E and mass M in a thermalized medium with temperature T has been calculated in several papers with different approaches [40]. In our calculations, the collisional energy loss of HQs in QGP by considering "Hard and Soft Thermal Loops" are given as follows [41].…”

“…where v is the HQ speed, α s is the strong coupling constant, n f is the number of quark flavors in the medium, E and M are energy and mass of the propagated HQ respectively, m g = (1 + n f /6)g 2 T 2 /3 is the thermal gluon mass, g = √ 4πα s is the gauge coupling parameter and B(v) is a smooth velocity function, which can be taken approximately as 0.7 [41].…”