Radiative energy-loss of heavy quarks in a quark-gluon plasma

Abstract

We estimate the radiative energy-loss of heavy quarks, produced from the initial fusion of partons, while propagating in a quark-gluon plasma which may be formed in the wake of relativistic heavy ion collisions. We find that the radiative energy-loss for heavy quarks is larger than the collisional energy-loss for all energies. We point out the consequences on possible signals of the quark-gluon plasma.One of the most interesting predictions of QCD is the transition from the confined/chirally broken phase to the deconfined/chirally symmetric state of quasi-free quarks and gluons, the so-called quark-gluon plasma (QGP). Relativistic heavy ion collisions are being studied with the intention of investigating the properties of the QGP [1]. While experiments at AGS and SPS continue, new experiments have been planned at RHIC and LHC with centre of mass energies 200 AGeV and 5.5 ATeV, respectively. During the past decade many different signatures of the transition to the QGP have been proposed. A promising example is the emission of penetrating probes such as dileptons and single photons, which can reveal the early parton dynamics and the history of evolution of the plasma. Similarly, the production and propagation of open charm and high energy jets in a dense medium, can provide information [2] about parton scattering and thermalization of the partonic system. Jets are expected to show up at collider energies at RHIC and LHC.Heavy quark pairs are mostly produced from the initial fusion of partons (mostly from gg → QQ, but also from qq → QQ, where q denotes one of the lighter quarks and Q is a heavy quark) of the colliding nucleons and also from the QGP, if the initial temperature is high enough, which is likely to be achieved at RHIC and LHC energies. The charm quarks will be produced on a time scale of 1/2m c 0.07 fm/c, which would be as low as 0.02 fm/c for bottom quarks. There is no production of heavy quarks at late times in the QGP and none in the hadronic matter. Thus, the total number of heavy quarks gets frozen very early in the history of the collision which makes them a good candidate for a probe of the QGP. Immediately upon their production, these heavy quarks will propagate through the deconfined matter and start losing energy. The energy-loss suffered by these quarks will determine the shape of the dilepton spectra produced from correlated charm (or bottom) decay which provides a large background to dilepton production from annihilation of quarks in the plasma. We shall come back to this aspect towards the end of this Letter.There are two contributions to the energy-loss of a heavy quark in the QGP: one caused by elastic collisions with the light partons of the QGP and the other by radiation of the decelerated color charge, i.e., bremsstrahlung of gluons. There is an extensive body of literature [3][4][5][6][7][8] on the collisional energy-loss of energetic quarks considering elastic collisions with the quarks and gluons (Qg → Qg and Qq → Qq) of the dense medium. A complete leading order result for the col...

Heavy quark radiative energy loss in QCD matter

“…These should be approximately the same if the elastic rescattering and the hard unitarity correction terms cancel as in Eq. (27). We find that the GB energy loss for E=10 GeV charm quarks is ∆E GB /E ≈ 0.35 is significantly larger than the incoherent energy loss ∆E in /E ≈ 0.22.…”

HighpTnonphotonic electron production inp+pcollisions ats=200 Agakishiev1, Aggarwal2, Ahammed3 et al. 2011Phys. Rev. D533240View full textAdd to dashboardCite

“…Many effects on heavy flavor production in heavyion collisions have been observed but are quantitatively not yet fully understood [4]. Of particular interest are effects which modify the transverse momentum spectra of heavy flavor hadrons, including energy loss in the QGP ("jet quenching") [5][6][7][8][9], as well as collective effects such as elliptic flow [10,11]. In addition, J/ψ might be regenerated in a dense plasma from the initial open charm yield [12], making precise measurements of the transverse momentum spectra in elementary p+p collisions imperative.…”

Bottomonium production atsNN=200GeV andsNNGrandchamp1, Lumpkins2, Sun3 et al. 2006Phys. Rev. C9171100View full textAdd to dashboardCite

“…The effectiveness of recombination mechanisms in statistical and kinetic models sensitively resides on a thermal equilibration of the charm-(c-) quark momentum distributions in the QGP [13,14]. On the one hand, kinetic c-quark equilibrium is not easily conceivable based on perturbative QCD (pQCD) cross sections with thermal light quarks and gluons [15][16][17][18]. On the other hand, a recent study based on resonant rescattering via "D"-meson states in the QGP [17] found substantially smaller c-quark thermalization times (by about a factor of ∼3 compared to pQCD estimates), being comparable to or even below the expected QGP lifetime at RHIC.…”