Induced gluon radiation in a QCD medium

Abstract

Soft gluon radiation induced by multiple scattering of a fast quark or gluon propagating through QCD matter is discussed. After revisiting the Landau-Pomeranchuk-Migdal effect in QED we show that large formation times of bremsstrahlung quanta determine the QCD radiation intensity (in analogy to QED) and derive the gluon energy spectrum. Coherent suppression takes place as compared to the Bethe-Heitler situation of independent emissions. As a result the energy loss of fast partons in a QCD medium depends on the incident energy E similarly to QED, −dE/dz ∝ √ E. † Permanent address: Petersburg Nuclear Physics Institute,

Parton energy loss and modified beam quark distribution functions in Drell–Yan process in collisions

“…Multiple scattering and induced parton energy loss have been studied in several theoretical frameworks [26][27][28][29], among which the higher-twist approach can be applied to jet propagation in both hot QGP and cold nuclei. In high-energy heavy-ion collisions, energetic partons which one uses as hard probes have to traverse not only the hot QGP in the early stage of the dense matter but also hadronic medium after hadronization of the QGP matter.…”

Jet (de)coherence in Pb–Pb collisions at the LHC

“…This comes about due to the large separation of the intrinsic jet scale Q ≡ Θ jet p ⊥ and the characteristic momentum scale of the medium Q s , to be defined below, such that Q Q s Λ QCD , where Λ QCD is the non-perturbative scale of QCD. This scale separation is also intimately related to the interplay of two main mechanisms: induced independent gluon radiation off the coherent jet [10,11], which stands for the dominant medium effect, and corrections due to partial color decoherence of its constituents [12]. The former component is responsible for radiative energy loss and, in particular, for transporting this energy up to very large angles.…”

“…At high p ⊥ this is caused by energy loss due to medium induced radiation [10]. Presently we will assume that these jets are mainly induced by primary quarks arXiv:1401.8293v1 [hep-ph] 31 Jan 2014 and parameterize the vacuum spectrum by a power law,…”

“…The equation is governed by the branching rate, of parton j into parton i, per unit time, K ij (z, p ⊥ ; t), which can be derived directly from the one-gluon emission spectrum [10],…”

“…(5), which practically removes them from the cone. However, by comparing the minimal angle for induced radiation Θ c = (qL 3 12) − 1 /2 [10,11], which with our set of parameters corresponds to ∼ 0.08, to the typical jet reconstruction radius, presently considered to be Θ jet = 0.3. This implies that subleading structures of the jet are resolved by the medium [3,12].…”