title: Angular Structure of the In-Medium QCD Cascade.
abstract: We study the angular broadening of a medium-induced QCD cascade. We derive the equation that governs the evolution of the average transverse momentum squared of the gluons in the cascade as a function of the medium length, and we solve this equation analytically. Two regimes are identified. For a medium of a not too large size, and for not too soft gluons, the transverse momentum grows with the size of the medium according to standard momentum broadening. The other regime, visible for a medium of a sufficiently large size and very soft gluons, is a regime dominated by multiple branchings: there, the average transverse momentum saturates to a value that is independent of the size of the medium. This structure of the in-medium QCD cascade is, at least qualitatively, compatible with the recent LHC data on dijet asymmetry.
authors.affiliation: Institut de Physique Théorique (IPhT) Saclay, CNRS/URA2306, F-91191 Gif-sur-Yvette, France.
authors.forename: J-P
authors.initials: JP
authors.lastname: Blaizot
authors.affiliation: Institut de Physique Théorique (IPhT) Saclay, CNRS/URA2306, F-91191 Gif-sur-Yvette, France.
authors.forename: Y
authors.initials: Y
authors.lastname: Mehtar-Tani
authors.affiliation: Institut de Physique Théorique (IPhT) Saclay, CNRS/URA2306, F-91191 Gif-sur-Yvette, France.
authors.forename: M A C
authors.initials: MA
authors.lastname: Torres