Abstract
Abstract We study the radiation of a highly energetic partonic antenna in a colored state traversing a dense QCD medium. Resumming multiple scatterings of all involved constituents with the medium we derive the general gluon spectrum which encompasses both longitudinal color coherence between scattering centers in the medium, responsible for the well known Landau-Pomeranchuk-Migdal (LPM) effect, and transverse color coherence between partons inside a jet, leading, in vacuum, to angular ordering of the parton shower. We discuss shortly the onset of transverse decoherence which is reached in opaque media. In this regime, the spectrum consists of independent radiation off the antenna constituents.
Highlights
We study the radiation of a highly energetic partonic antenna in a colored state traversing a dense QCD medium
Since the process under consideration does not deal with interference effects between emitters, see section 2, the extension to multi-gluon emissions is bound to rely on ad hoc conjectures
The key result of this work is the derivation of the interference spectrum, cf. eq (4.16), while a complete and detailed discussion of the emerging physical picture is presented in [26, 28], see [29] for a complementary discussion
Summary
Coherence phenomena in jet physics have been extensively studied in the framework of perturbative QCD since the early 80’s (see, e.g., [30,31,32,33] and references therein). In the case of in-medium radiation, another type of coherence arises which we, in contrast to the above, will call “longitudinal coherence”, namely, when the medium is dense enough an energetic particle can scatter coherently off several scattering centers along its trajectory during its formation time, tform ∼ Ncohλ (λ being the mean free path in the medium and Ncoh the number of coherent scattering centers) It was realized a some time ago that this is analogous to the Landau-Pomeranchuk-Migdal (LPM) effect known fro√m QED. For the study of jet evolution in heavy-ion collisions it seems imperative to incorporate both the transverse and longitudinal coherence phenomena Such a unified approach is missing to date.
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