Jet Quenching Signatures From Very High Pt Dihadron Correlations In Pb Pb Collisions At Square Root Of S Nn
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Jet-quenching Signatures from Very High-pT Dihadron Correlations in Pb+Pb Collisions at Square Root of S NN
Experimental measurements from dihadron correlations triggered with very high-p[subscript]T particles in Pb+Pb collisions at 2.76 TeV are shown. The data set was collected by the Compact Muon Solenoid (CMS) detector at the Large Hadron Collider (LHC) and corresponds to an integrated luminosity of 150 [mu]b−1. The use of high-p[subscript]T track triggers made it possible to study dihadron correlations up to p[subscript]T ~ 50 GeV/c. The presence of azimuthal anisotropies of final state particles in non-central Pb+Pb collisions gives rise to single-particle correlations that are characterized by the Fourier harmonics, v[subscript]n. To isolate the jet components of the correlations, the v2-v4 components are subtracted from the correlations and the per-trigger-particle associated-yields on the near and away side are studied. The data are compared to correlations from p+p collisions at the same center-of-mass energy over a wide range of trigger and associated-particle p[subscript]T and as a function of Pb+Pb event centrality. On the near-side there is evidence of moderate enhancement at low p[superscript]assc [subscript]T. On the away side there is a significant enhancement at p[superscript]assc [subscript]T ~ 0.5 GeV/c and at higher transverse momentum, p[superscript]assc [subscript]T > 3 GeV/c, there is a suppression of about 50% compared to p+p collisions.
Study of Jet Quenching with Z+jet Correlations in PbPb and Pp Collisions at $\sqrt{s_{NN}}$
The production of jets in association with Z bosons, reconstructed via the mu+mu- and e+e- decay channels, is studied in pp and, for the first time, in PbPb collisions. Both data samples were collected by the CMS experiment at the LHC, at a center-of-mass energy of 5.02 TeV. The PbPb collisions were analyzed in the 0-30% centrality range. The back-to-back azimuthal alignment was studied in both pp and PbPb collisions for Z bosons with transverse momentum ptz> 60 GeV/c and a recoiling jet with ptj> 30 GeV/c. The pt imbalance, xjz= ptj/ptz, as well as the average number of jet partners per Z, rjz, were studied in intervals of ptz, in both pp and PbPb collisions. The rjz is found to be smaller in PbPb than in pp collisions, which suggests that in PbPb collisions a larger fraction of partons, associated with the Z bosons, lose energy and fall below the 30 GeV/c ptj threshold.
Correlations Between Jets and Charged Particles in PbPb and Pp Collisions at $ \sqrt{s_{\mathrm{NN}}}
In this study, the 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 luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at $ \sqrt{s_{\mathrm{NN}}}=2.76 $ TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity ([Delta][eta]) and relative azimuthal angle ([Delta][Phi]) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum (pT) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in pT, 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 pT. A centrality-dependent excess of low-pT particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-pT particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of [Delta][eta] ≈ 1 and [Delta][Phi] ≈ 1.