CMS-PAS-HIN-15-013 | ||
Study of Z+jet correlations in PbPb and pp collisions at √sNN= 5.02 TeV | ||
CMS Collaboration | ||
May 2016 | ||
Abstract: The production of Z+jet pairs is measured for the first time in pp and central PbPb collisions at a centre-of-mass energy of 5.02 TeV per nucleon pair, using data samples collected by the CMS experiment at the LHC. The Z+jet azimuthal angle correlations and pT imbalance are analysed for events containing a Z boson with transverse momentum pZT> 60 GeV/c and an associated jet with pJetT> 30 GeV/c. A moderate shift in the pJetT/pZT ratio is seen in central PbPb collisions with respect to the ratio found using pp data. | ||
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inSPIRE record ;
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These preliminary results are superseded in this paper, PRL 119 (2017) 082301. The superseded preliminary plots can be found here. |
Figures | |
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Figure 1-a:
Dimuon invariant mass distributions of Z boson candidates in pp collisions (a) and in 0-30% centrality PbPb collisions (b), as measured (circles) and simulated (filled histogram). |
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Figure 1-b:
Dimuon invariant mass distributions of Z boson candidates in pp collisions (a) and in 0-30% centrality PbPb collisions (b), as measured (circles) and simulated (filled histogram). |
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Figure 2-a:
Dielectron invariant mass distributions of Z boson candidates in pp collisions (a) and in 0-30% centrality PbPb collisions (b), as measured (circles) and simulated (filled histogram). |
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Figure 2-b:
Dielectron invariant mass distributions of Z boson candidates in pp collisions (a) and in 0-30% centrality PbPb collisions (b), as measured (circles) and simulated (filled histogram). |
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Figure 3:
Normalized number of Z+jet pairs before (black squares) and after (red circles) mixed-event background subtraction. The distribution of the Z+jet pairs from the mixed event method is also shown, as blue triangles. |
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Figure 4-a:
Azimuthal angle correlation ΔϕJZ between the Z boson and the jet (a), and transverse momentum ratio xJZ between the Z boson and the jets, with the azimuthal angle separation ΔϕJZ> 7/8π (b). The distributions are normalized by the number of Z boson events. Transverse momentum thresholds are pZT> 60 GeV/c for Z bosons and pJetT> 30 GeV/c for jets. The mean of the xJZ distributions in PbPb and pp data are indicated with red and green arrows, respectively. |
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Figure 4-b:
Azimuthal angle correlation ΔϕJZ between the Z boson and the jet (a), and transverse momentum ratio xJZ between the Z boson and the jets, with the azimuthal angle separation ΔϕJZ> 7/8π (b). The distributions are normalized by the number of Z boson events. Transverse momentum thresholds are pZT> 60 GeV/c for Z bosons and pJetT> 30 GeV/c for jets. The mean of the xJZ distributions in PbPb and pp data are indicated with red and green arrows, respectively. |
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Figure 5-a:
Azimuthal angle correlation ΔϕJZ (a) and transverse momentum ratio xJZ after the ΔϕJZ> 7/8π cut (b), as measured in pp data (circles) and simulated with PYTHIA and MadGraph5-aMC@NLO MC (filled histograms). The distributions are normalized by the number of Z boson events. Transverse momentum thresholds are pZT> 60 GeV/c for Z bosons and pJetT> 30 GeV/c for jets. |
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Figure 5-b:
Azimuthal angle correlation ΔϕJZ (a) and transverse momentum ratio xJZ after the ΔϕJZ> 7/8π cut (b), as measured in pp data (circles) and simulated with PYTHIA and MadGraph5-aMC@NLO MC (filled histograms). The distributions are normalized by the number of Z boson events. Transverse momentum thresholds are pZT> 60 GeV/c for Z bosons and pJetT> 30 GeV/c for jets. |
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Figure 6-a:
The mean value of the xJZ distribution as a function of the Z boson transverse momentum (a) and the RJZ probability to find a back-to-back jet partner for a Z boson candidate (b). |
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Figure 6-b:
The mean value of the xJZ distribution as a function of the Z boson transverse momentum (a) and the RJZ probability to find a back-to-back jet partner for a Z boson candidate (b). |
Tables | |
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Table 1:
Number of events surviving each selection step, for the pp and 0-30% centrality PbPb collisions. |
Summary |
This is the first study of Z+jet correlations in PbPb collisions, made with the CMS experiment. The collisions of PbPb and pp at 5.02 TeV center-of-mass energy, corresponding to an integrated luminosity of 404 μb−1 and 25.8 pb−1, respectively, were collected during the 2015 data-taking period. The Z+jet correlations were studied using the transverse momentum ratio xJZ, the azimuthal angle correlation ΔϕJZ, and the probability to find a back-to-back jet partner RJZ. The Z boson and jets were required to have transverse momentum greater than 60 GeV/c and 30 GeV/c, respectively. The transverse momentum ratio xJZ for the 0-30% centrality PbPb collisions is shifted to lower values with respect to pp collisions. The study of the average value of the transverse momentum ratio in Z boson pT bins shows that <xJZ> is systematically smaller for PbPb collisions than in pp for all pT bins with pZT> 60 GeV/c. These observations are in agreement with expected jet quenching effects. For all Z boson pT bins, RJZ in PbPb collisions is lower than in pp collisions, which suggests that in PbPb collisions a larger fraction of partons associated with the Z boson lost energy and fell below the 30 GeV/c jet pT threshold. |
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Compact Muon Solenoid LHC, CERN |
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