Abstract
CThe quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosi- ties of 166 μb$^{−1}$ and 5.3 pb$^{−1}$, respectively, collected at $\sqrt{^{s}NN}$ = 2.76 TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity (∆η) and relative azimuthal angle (∆φ) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum ($p_{T}$) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in $p_{T}$, respectively) in a selection of back-to-back dijet events. Modifications in PbPb data relative to pp reference data are characterized as a function of PbPb collision centrality and charged particle $p_{T}$. A centrality-dependent excess of low-$p_{T}$ particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-$p_{T}$ particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of ∆η ≈ 1 and ∆φ ≈ 1.
CMS Collaboration