Correlations Between Jets and Charged Particles in PbPb and Pp Collisions at √sNN PDF Download
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Author: CMS Collaboration
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Languages : en
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Author: CMS Collaboration
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ISBN:
Category :
Languages : en
Pages :
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Author:
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Languages : en
Pages : 39
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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.
Author: Frank Teng Ma
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Languages : en
Pages : 163
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In this thesis the jet fragmentation function of inclusive jets with transverse momentum PT > 100 GeV/c in PbPb collisions is measured for reconstructed charged particles with PT > 1 GeV/c within the jet cone. A data sample of PbPb collisions collected in 2011 at a center-of-mass energy of [square root of]sNN = 2.76 TeV corresponding to an integrated luminosity of 150 [mu]b-1 is used. The results for PbPb collisions as a function of collision centrality are compared to reference distributions based on pp data collected at the same collision energy. A centrality-dependent modification of the fragmentation function is revealed. For the most central collisions a significant enhancement is observed in the PbPb/pp fragmentation function ratio for the charged particles with PT less than 3 GeV/c.
Author: Doga Can Gulhan
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Languages : en
Pages : 232
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Two dijet measurements, one using 35 pb-1 pPb data at [square root]sNN- 5.02 TeV, and another with 166 [mu]b-1 PbPb and 5.3 pb-1 pp data at [square root]sNN = 2.76 TeV collected with CMS detector at the LHC, are presented. In pPb collisions, the dijet PT ratios, azimuthal angle differences and pseudorapidity distributions are measured and compared to PYTHIA and PYTHIA+HIJING simulations as well as NLO QCD predictions for the latter observable. No significant signs of final state interactions, such as a decrease in the mean dijet PT ratios or a broadening in the correlation of the dijets in azimuthal angle, with increasing forward activity, are observed. The dijet pseudorapidity distributions are also measured, and are sensitive to nuclear PDFs for x values of 0.001 - 0.5. Selections on event activity are found to yield unexpected centrality biases on dijet pseudorapidity distributions, which aided the interpretation of similar biases seen in inclusive jet measurements by ATLAS. In PbPb collisions, a detailed scan of charged particle distributions in correlation with the dijet system is carried out. The PT projection of charged particles on the dijet axis is measured at different distances of [delta] = [mathematical formula ...] 2 with respect to the leading and subleading jet axes. In this way, the spectra and angular distribution of the additional particles, which recover the overall event balance in dijet events with enhanced PT asymmetry in PbPb compared to pp collisions, are obtained up to [delta] = 1.8 in steps of 0.2. A significant excess of low PT particles associated with a subleading jet at large [delta] values is observed, and this excess is shown to get larger for dijet events with PT asymmetry. The scan is carried out for variety of anti-kT R parameters, which provides a way of varying jet width and fragmentation. Medium response to jet quenching at wide angles for jets with different fragmentation is studied. Only an insignificant increase of the magnitude of low PT particle excess at large angles, but a significant increase in the modification of the balance distribution close to the jet axes is observed by increasing R.
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Languages : en
Pages : 26
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Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 inverse microbarns. Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cut-off used in this study (jet transverse momentum = 120 GeV/c) up to the statistical limit of the available data sample (jet transverse momentum approximately 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet.
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Languages : en
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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_{\mathrm{N}\;\mathrm{N}}}=2.76 $ TeV with integrated luminosities of 166 [mu]b-1 and 5.3 pb-1, respectively, by the CMS experiment at the LHC. Furthermore, 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.
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Languages : en
Pages : 21
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The first measurement of jet shapes, defined as the fractional transverse momentum radial distribution, for inclusive jets produced in heavy-ion collisions is presented. Data samples of PbPb and pp collisions, corresponding to integrated luminosities of 150 inverse microbarns and 5.3 inverse picobarns respectively, were collected at a nucleon-nucleon centre-of-mass energy of sqrt(s[NN]) = 2.76 TeV with the CMS detector at the LHC. The jets are reconstructed with the anti-kt algorithm with a distance parameter R=0.3, and the jet shapes are measured for charged particles with transverse momentum pt> 1 GeV. The jet shapes measured in PbPb collisions in different collision centralities are compared to reference distributions based on the pp data. A centrality-dependent modification of the jet shapes is observed in the more central PbPb collisions, indicating a redistribution of the energy inside the jet cone. This measurement provides information about the parton shower mechanism in the hot and dense medium produced in heavy-ion collisions.
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Languages : en
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The per-event yield of the highest transverse momentum charged particle and charged-particle jet, integrated above a given pminT threshold starting at pminT=0.8 and 1 GeV, respectively, is studied in pp collisions at s√=8 TeV. Furthermore, the particles and the jets are measured in the pseudorapidity ranges.
Author: Shreyasi Acharya
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Languages : en
Pages : 0
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Author:
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Category :
Languages : en
Pages : 23
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