Two-particle angular correlations in pp and heavy-ion collisions

This paper presents a selected review of recent experimental results on two-particle angular correlations in AuAu and pp collisions. Two-particle correlations in AuAu collisions exhibit a rich structure as a function of hadron transverse momentum, carrying information about the expansion of the medium produced in nuclear collisions, the energy loss of high-pT partons in the medium and the medium response to these high-pT partons or other initial state inhomogeneities. Evidence on the interplay between initial state fluctuations and the final state correlation structure is discussed.