Anomalous evolution of the near-side jet peak shape in Pb-Pb collisions with ALICE

Abstract

Two-particle angular correlations are sensitive probes to study the interaction of jets with the flowing medium produced in heavy-ion collisions. These interactions may appear as modifications of the near-side jet peak compared to pp collisions. In these measurements, the associated per-trigger yield is calculated from the relative azimuthal angle and pseudorapidity between a trigger particle with higher $p_{\mathrm{T}}$ (1 GeV/c $<p_{\mathrm{T}}<8$ GeV/c) and an associated particle. Subsequently, the near-side peak width and shape are extracted as a function of $p_{\mathrm{T}}$ and centrality. Results obtained by the ALICE detector from Pb-Pb and pp collisions are presented. In Pb-Pb collisions, a significant broadening of the peak in central events at low $p_{\mathrm{T}}$ is observed in the data, and is more pronounced in the $\Delta \eta$ direction than in the $\Delta \phi$ direction. A novel feature is also observed at low $p_{\mathrm{T}}$ in central events: the peak departs from the Gaussian shape, and a depletion around its center appears. To put the broadening and the depletion in context with the strength of longitudinal, radial and elliptic flow, the results are compared to AMPT simulations, which suggest that radial and longitudinal flow play a significant role in the appearance of the observed features.

arXiv comment4 pages, 3 figures. Submitted to the proceedings of Rencontres de Moriond QCD and High Energy Interactions 2017