Effect of jet quenching on hydrodynamical evolution of QGP

Abstract

We study the effects of jet quenching on the hydrodynamical evolution of the quark-gluon plasma (QGP) fluid created in a heavy-ion collision. In jet quenching, a hard QCD parton, before fragmenting into a jet of hadrons, deposits a fraction of its energy in the medium, leading to suppressed production of high-pT hadrons. Assuming that the deposited energy quickly thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP fluid. For partons moving at supersonic speed, vp > cs, and sufficiently large energy loss, a shock wave forms leading to conical flow [1]. The PHENIX Collaboration recently suggested that observed structures in the azimuthal angle distribution [2] might be caused by conical flow. We show here that, for phenomenologically acceptable values of parton energy loss, conical flow effects are too weak to explain these structures.PACS numbers: PACS numbers: 13.85.Hd, Recent Au+Au collision experiments at the Relativistic Heavy Ion Collider (RHIC) saw a dramatic suppression of hadrons with high transverse momenta ("highp T suppression") [3], and the quenching of jets in the direction opposite to a high-p T trigger particle [4,5], when compared with p+p and d+Au collisions. This is taken as evidence for the creation of a very dense, color opaque medium of deconfined quarks and gluons [6]. Independent evidence for the creation of dense, thermalized quark-gluon matter, yielding comparable estimates for its initial energy density ( e > ∼ 10 GeV/fm 3 at time τ therm < ∼ 0.6 fm/c [7]), comes from the observation of strong elliptic flow in non-central Au+Au collisions [3], consistent with ideal fluid dynamical behaviour of the bulk of the matter produced in these collisions.These two observations raise the question what happens, in the small fraction of collision events where a hard scattering produces a pair of high-p T partons, to the energy lost by the parton travelling through the medium. The STAR Collaboration has shown that, while in central Au+Au collisions there are no hard particles left in the direction opposite to a high-p T trigger particle, one sees enhanced production (compared to p+p) of soft (low-p T ) particles, broadly distributed over the hemisphere diametrically opposite to the trigger particle [8]. This shows that the energy of the fast parton originally emitted in the direction opposite to the trigger particle is not lost, but severely degraded by interactions with the medium. As the impact parameter of the collisions decreases, the average momentum of the particles emitted opposite to the trigger particle approaches the mean value associated with all soft hadrons, i.e. the p T of the thermalized medium [8]. This suggests that the energy lost by the fast parton has been largely thermalized. Nevertheless, this energy is deposited locally along the fast parton's trajectory, leading to local energy density inhomogeneities which, if thermalized, should in turn evolve hydrodynamically. This would modify the usual hydrodynamic expansion of the collision fireball as observed in t...

Universality of the diffusion wake in the gauge-string duality

“…Another study [51] included expansion of the plasma and used source terms similar to scenario 1. It also concluded that a minimum at δφ = π is hard to achieve.…”

“…It is natural for us to hope that a diffusion wake really is generated when a hard parton traverses a quark-gluon plasma, but that it is erased or disguised in the data. More realistic theoretical treatments should include expansion of the plasma, as in [51,52,53] and perhaps also a more sophisticated treatment of hadronization; as compared to the sonic boom, the diffusion wake is deeper inside the expanding medium, so it has more chance to broaden, soften, and thermalize before freeze-out. Some hints of this were observed in [51].…”

“…More realistic theoretical treatments should include expansion of the plasma, as in [51,52,53] and perhaps also a more sophisticated treatment of hadronization; as compared to the sonic boom, the diffusion wake is deeper inside the expanding medium, so it has more chance to broaden, soften, and thermalize before freeze-out. Some hints of this were observed in [51]. There also issues of detector acceptance which may be relevant, see for example the discussion in [53].…”

Conical Flow from Quenched Jets in sQGP

“…It is also strongly dependent on jet quenching deposition dE/dx, as demonstrated in Fig.3(a). But mostly it is sensitive to viscosity: since the conical flow has larger gradients 10 It does not matter whether hydro is or is nor linearized: thus Chaudhuri and Heinz [46] could not possibly resolve the issue as well, they just made an arbitrary selection. The only approach which does not have this problem is AdS/CFT, to be discussed below.…”

Centrality and transverse momentum dependence of dihadron correlations in a hydrodynamic model

“…Theoretically, the latter is described by Quantum Chromodynamics (QCD) [1,2]. After the collisions, the system evolves hydrodynamically, cooling and becoming more diluted until it reaches the instant of thermal freeze-out τ , where the system decouples, and the hadronic particles do not interact any more [3,4]. The QGP state of matter can be explored by investigating the final hadrons, especially those created in hard processes whose trajectories traverse the entire system [5].…”