The radiation pattern of a QCD antenna in a dilute medium

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, $r_\perp^{-1}$, 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, $ _{\text{med}}\sim \text{max}(r_\perp^{-1},m_D)$. Above the hard scale interference effects suppress the spectrum resulting in the restoration of vacuum coherence.