The role of gluons in dilepton production from the quark–gluon plasma

Abstract

We study high mass dilepton production from gluon-induced processes, gq → qγ * , gq →qγ * , and gg → qqγ * , in a thermally equilibrated but chemically under-saturated partonic matter that is expected to be created in the initial stage of ultra-relativistic heavy ion collisions. Regulating the divergence in these processes by the thermal quark mass, we find that gluon-induced processes are more important than the leading-order qq annihilation process as a result of the larger number of gluons than quarks in the partonic matter. The dependence of the thermal dilepton yield from the partonic stage of heavy ion collisions on the initial conditions for the partonic matter is also studied. We further discuss the feasibility of observing thermal dileptons from the quark-gluon plasma in heavy ion experiments.

Multiphase transport model for relativistic heavy ion collisions

“…Although this is unphysical as one expects gluons to dominate the initial stage of ultra-relativistic heavy ion collisions, our study of the elliptic flow [45] and the pion interferometry [48] depends more on the effect of partonic scatterings instead of the composition of the partonic matter. However, for dilepton production from the partonic matter, the flavor composition of the partonic matter is important [240], and at present they cannot be addressed within the AMPT model. To extend the string melting scenario to include gluons in the AMPT model, we need to study the problem of both quark-antiquark and gluon production from a strong color field.…”

Signatures of thermal dilepton radiation at ultrarelativistic energies

“…As shown in ref. [15] related contributions are comparable to qq production in a more extreme scenario of undersaturation with λ g /λ q ≃ 10. Since in our case λ g /λ q < 3 after τ = 1 fm/c (and quickly decreasing further), we keep ignoring α s -corrections (as done for the equilibrium case) being aware of possibly underestimating the thermal yield from the off-equilibrium plasma by a few tens of percent.…”

“…[65]). On the other hand, Lin and Ko, using initial conditions estimated from perturbative-QCD [64], find very strong suppression of the thermal yield which comes out well below Drell-Yan annihilation [15]. The employed initial conditions, λ q,0 = λq ,0 = 0.0072, λ g,0 = 0.06 and T 0 = 570 MeV, correspond to an entropy density of s 0 ≃ 12 fm −3 , which is an order of magnitude smaller than in the SSPC approach adopted here (eqs.…”

“…For the IMR various interplays have been elaborated in refs. [6][7][8][9][10][11][12][13][14][15], and for the LMR assessments have been made, e.g., in ref. [16].…”

Dilepton production by dynamical quasi-particles in the strongly interacting quark–gluon plasma

“…First concepts of the QGP were guided by the idea of a system of partons which interact weakly with pQCD cross sections. Consequently, early predictions of the dilepton emission from the QGP relied on perturbative formulae for the cross sections of the virtual photon production in q + q and q+g collisions [4,22,23]. Due to large running coupling, the next-to-leading order (NLO) gluon-quark interactions contribute considerably in addition to the leading order (Born) mechanism of quark-quark annihilation (q q → l + l − ) to the QGP radiation spectrum [24], while the effect of multiple scattering of the quark in the plasma (Landau-Pomeranchuk-Migdal effect [25][26][27]) on the rate of q q → γ * was stressed in [28].…”