Near-side jet peak broadening in Pb-Pb collisions at $\sqrt{s_{NN}} = 2.76$ TeV

Abstract

Two-particle angular correlation measurements are sensitive probes of the interactions of particles with the medium formed in heavy-ion collisions. Such measurements are done by determining the distribution of the relative pseudorapidity ($\Delta\eta$) and azimuthal angle ($\Delta\varphi$) of particles with respect to a higher $p_T$ trigger particle ($1 < p_{T,trig} < 8$ GeV/c). The near-side peak is fitted with a function, which includes both the near-side jet peak and also accounts for the $\Delta\eta$-independent long-range correlations. The centrality evolution of the width (variance) of the fitted distribution is investigated. In Pb-Pb collisions a significant broadening of the near-side peak in the $\Delta\eta$ direction is observed from peripheral to central collisions, while in the $\Delta\varphi$ direction the peak is almost independent of centrality. For the 10% most central events, a departure from the Gaussian shape is also observed at low transverse momentum ($1 < p_{T,assoc} < 2$ GeV/c, $1 < p_{T,trig} < 3$ GeV/c). In this contribution the results obtained by the ALICE experiment in Pb-Pb and pp collisions at $\sqrt{s_{NN}} = 2.76$ TeV are shown, and they are interpreted in terms of radial and elliptic flow by comparing them to AMPT model simulations.