Using di-hadron correlations to investigate jet modifications in Pb--Pb collisions with ALICE

Abstract

The comparison of jets measured in heavy-ion collisions with jets measured in pp collisions is a rich source of information on jet-medium interactions. These medium-induced modifications can be prominent at low transverse momentum $p_{\rm{T}}$, where traditional jet reconstruction tools are difficult to use. The measurement of di-hadron correlations provide an alternative way to study jets in this $p_{\rm{T}}$ regime. Calculating the pseudorapidity ($\Delta\eta$) and azimuthal angle ($\Delta\varphi$) differences between trigger and associated particles, one observes the manifestation of the jet fragmentation as a peak around ($\Delta\eta$,$\Delta\varphi$)=(0,0). The modification factor $I_{\rm{AA}}$ is defined as the yield of the jet-like peak in Pb-Pb divided by the corresponding yield in pp collisions at the same energy. In this contribution, we will present the latest ALICE measurements of $I_{\rm{AA}}$ with charged hadrons from collisions with a center of mass energy per nucleon-nucleon pair of 2.76 TeV. We observe that the $\Delta\eta$-dependent $I_{\rm{AA}}$ shows a narrowing in pseudorapidity in central collisions for trigger particles with a high $p_{\rm{T}}$. We also investigate the path-length dependence of jet modification by measuring $I_{\rm{AA}}$ as a function of the relative angle between the trigger particle and the event plane. These measurements are compared to model calculations, and are expected to place strong constraints on energy loss models.