Abstract
Abstract Radiative interferences in the multi-parton shower is the building block of QCD jet physics in vacuum. The presence of a hot medium made of quarks and gluons is expected to alter this interference pattern. To study these effects, we derive the gluon emission spectrum off a color-correlated quark-antiquark pair (antenna) traversing a colored medium to first order in the medium density. The resulting induced gluon distribution is found to be governed by the hardest scale of the problem. In our setup, this can either be the inverse antenna transverse size, $ r_{ \bot }^{{ - 1}} $ , or the scale related to the transverse color correlation length in the medium, which is given by the Debye mass m D . This emerging scale opens the angular phase space of emissions off the antenna compared to the vacuum case and gives rise to a typical transverse momentum of the medium-induced emitted gluons, $ {\left\langle {k_{ \bot }^2} \right\rangle_{{med}}} $ ~ max $ \left( {r_{ \bot }^{{ - 1}},{m_D}} \right) $ . Above the hard scale interference effects suppress the spectrum resulting in the restoration of vacuum coherence.
Highlights
The recent start-up of the highly versatile experimental program at the Large Hadron Collider (LHC) at CERN for collisions of both protons and nuclei motivates a closer look at medium effects on hard probes
√ metry [2, 3] in Pb+Pb collisions at sNN = 2.76 TeV reveal strong effects with respect to the p+p b√aseline. These initial results, together with the first jet studies in Au+Au collisions at sNN = 200 GeV performed at RHIC [4,5,6], mark the beginning of a new era for perturbative physics in heavy-ion collisions
Θ(cos θqq demonstrating that medium-induced soft gluon radiation is suppressed inside the cone of opening angle θqq, as opposed to the standard angular structure obtained in vacuum, see eq (2.24)
Summary
The recent start-up of the highly versatile experimental program at the Large Hadron Collider (LHC) at CERN for collisions of both protons and nuclei motivates a closer look at medium effects on hard probes. The purpose of this work is to overcome some of the limitations mentioned above, in particular studying the case of gluon emission off two emitters — a quark-antiquark pair formed initially in either a color singlet or a color octet state This setup allows to address the color coherence effects analogous to those responsible for angular ordering in vacuum. The medium-induced coherent spectrum differs significantly from the independent one [15,16,17,18,19,20,21] due to the inclusion of interference diagrams which were heretofore neglected These new contributions die out only in the case of very hard gluon emissions and for large opening angles of the pair.
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