Jet-track correlations in PbPb collisions at 2.76 TeV

Medium-induced changes to charged particle correlations associated with high momentum jets in PbPb collisions are explored by comparing such measurements to pp reference data. This jet-track correlation analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 $\mu \rm{b}^{-1}$ and 5.3 pb$^{-1}$, respectively, collected in 2011 and 2013 at collision energies of $\sqrt{s_{NN}} = 2.76$~TeV. The detailed angular distributions of all charged particles are studied as a function of $\Delta\eta$ and $\Delta\phi$ with respect to the jet axis, which provides a greater sensitivity to medium-induced modifications than has been achieved in previous measurements. Two jet samples are considered: an inclusive sample of high momentum jets, and a sample of dijets for which correlations to both leading and subleading jet axes are studied. Modifications of the correlated particle distributions are apparent in both relative pseudorapidity and relative azimuthal angle, and are found to extend to large $\Delta\eta$ and $\Delta\phi$ far beyond the typical hadron production ranges for vacuum fragmentation. A centrality-dependent excess of low-$p_{\rm T}$ particle yield is present for all jets studied, and is most pronounced in the most central events. This excess in the associated charged particle yield remains correlated with the jet axis following a Gaussian-like distribution, and is characterized in this analysis as a function of PbPb collision centrality and transverse momentum.