Abstract
Interactions between jets and the quark-gluon plasma produced in heavy ion collisions are studied via the angular distributions of summed charged-particle transverse momenta (pt) with respect to both the leading and subleading jet axes in high-pt dijet events. The contributions of charged particles in different momentum ranges to the overall event pt balance are decomposed into short-range jet peaks and a long-range azimuthal asymmetry in charged-particle pt. The results for PbPb collisions are compared to those in pp collisions using data collected in 2011 and 2013, at collision energy sqrt(s[NN]) = 2.76 TeV with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, by the CMS experiment at the LHC. Measurements are presented as functions of PbPb collision centrality, charged-particle pt, relative azimuth, and radial distance from the jet axis for balanced and unbalanced dijets.
Highlights
To those in pp collisions using data collected in 2011 and 2013, at collision energy sNN = 2.76 TeV with integrated luminosities of 166 μb−1 and 5.3 pb−1, respectively, by the CMS experiment at the LHC
The sample is divided into balanced (AJ < 0.22) and unbalanced (AJ > 0.22) dijet events, and the overall subleadingto-leading hemisphere momentum balance is evaluated by subtracting the distribution of ptTrk about the leading jet from the distribution of ptTrk about the subleading jet
Subtracting the long-range part of the correlation from the jet peaks, this work extends the studies of jet shape modifications in PbPb events relative to pp collisions to large radial distances (∆r ≈ 1) from the jet axis
Summary
It is found that low-pT particles extending to large angles away from the dijet axis in the subleading hemisphere must be considered in order to recover the momentum balance in these events In addition to these momentum balance studies, precise measurements of the fragmentation pattern [10] and the distribution of charged-particle pT as a function of radial distance from the jet axis [11], have shown that the jet structure is modified by the medium. Pp data taken in 2013 at the same energy corresponding to an integrated luminosity of 5.3 pb−1 are used These studies allow for a detailed characterization of the two-dimensional (in ∆η and ∆φ) ptTrk distributions for charged-particle tracks with respect to the jet axes, providing information about the topology of the event from the jet perspective and details about the ptTrk flow modification in dijet events.
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