Anisotropic particle production and azimuthal correlations in high-energy pA collisions (1503.03897v1)

Abstract: We summarize some recent ideas relating to anisotropic particle production in high-energy collisions. Anisotropic gluon distributions lead to anisotropies of the single-particle azimuthal distribution and hence to disconnected contributions to multi-particle cumulants. When these dominate, the four-particle elliptic anisotropy $c_2{4}$ changes sign. On the other hand, connected diagrams for $m$-particle cumulants are found to quickly saturate with increasing $m$, a coherence'' quite unlike conventionalnon-flow'' contributions such as decays. Finally, we perform a first exploratory phenomenological analysis in order to estimate the amplitude ${\cal A}$ of the $\cos(2\varphi)$ anisotropy of the gluon distribution at small $x$, and we provide a qualitative prediction for the elliptic asymmetry from three-particle correlations, $c_2{3}$.