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Using Z boson events to study parton-medium interactions in PbPb collisions

The CMS collaboration
CMS-HIN-19-006, 2021.

Abstract
The spectra measurements of charged hadrons produced in the shower of a parton originating in the same hard scattering with a leptonically decaying Z boson, are reported in lead-lead (PbPb) and proton-proton (pp) collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. Both PbPb and pp data sets are recorded by the CMS experiment at the LHC, and correspond to an integrated luminosity of 1.7 nb$^{-1}$ and 320 pb$^{-1}$, respectively. Hadronic collision data with one reconstructed Z boson candidate with the transverse momentum $p_\mathrm{T} \gt$ 30 GeV/$c$ are analyzed. The Z boson constrains the initial energy and direction of the associated parton. In heavy ion events, azimuthal angular distributions of charged hadrons with respect to the direction of a Z boson are sensitive to modifications of the in-medium parton shower and medium response. Compared to reference data from pp interactions, the results for central PbPb collisions indicate a modification of the angular correlations. The measurements of the fragmentation functions and $p_\mathrm{T}$ spectra of charged particles in Z boson events, which are sensitive to medium modifications of the parton shower longitudinal structure, are also reported. Significant modifications in central PbPb events compared to pp reference data are also found for these observables.

  • Table 1

    Data from top panel of Fig. 1

    10.17182/hepdata.95230.v1/t1

    Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in pp collisions at 5.02 TeV.

  • Table 2

    Data from top panel of Fig. 1

    10.17182/hepdata.95230.v1/t2

    Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in 70-90% centrality PbPb collisions at 5.02 TeV.

  • Table 3

    Data from top panel of Fig. 1

    10.17182/hepdata.95230.v1/t3

    Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in 50-70% centrality PbPb collisions at 5.02 TeV.

  • Table 4

    Data from top panel of Fig. 1

    10.17182/hepdata.95230.v1/t4

    Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in 30-50% centrality PbPb collisions at 5.02 TeV.

  • Table 5

    Data from top panel of Fig. 1

    10.17182/hepdata.95230.v1/t5

    Distributions of $\Delta\phi_{\mathrm{trk,Z}}$ in 0-30% centrality PbPb collisions at 5.02 TeV.

  • Table 6

    Data from bottom panel of Fig. 1

    10.17182/hepdata.95230.v1/t6

    PbPb - pp difference of $\Delta\phi_{\mathrm{trk,Z}}$ distributions for 70-90% centrality PbPb collisions at 5.02 TeV.

  • Table 7

    Data from bottom panel of Fig. 1

    10.17182/hepdata.95230.v1/t7

    PbPb - pp difference of $\Delta\phi_{\mathrm{trk,Z}}$ distributions for 50-70% centrality PbPb collisions at 5.02 TeV.

  • Table 8

    Data from bottom panel of Fig. 1

    10.17182/hepdata.95230.v1/t8

    PbPb - pp difference of $\Delta\phi_{\mathrm{trk,Z}}$ distributions for 30-50% centrality PbPb collisions at 5.02 TeV.

  • Table 9

    Data from bottom panel of Fig. 1

    10.17182/hepdata.95230.v1/t9

    PbPb - pp difference of $\Delta\phi_{\mathrm{trk,Z}}$ distributions for 0-30% centrality PbPb collisions at 5.02 TeV.

  • Table 10

    Data from top panel of Fig. 2

    10.17182/hepdata.95230.v1/t10

    Distributions of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ in pp collisions at 5.02 TeV.

  • Table 11

    Data from top panel of Fig. 2

    10.17182/hepdata.95230.v1/t11

    Distributions of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ in 70-90% centrality PbPb collisions at 5.02 TeV.

  • Table 12

    Data from top panel of Fig. 2

    10.17182/hepdata.95230.v1/t12

    Distributions of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ in 50-70% centrality PbPb collisions at 5.02 TeV.

  • Table 13

    Data from top panel of Fig. 2

    10.17182/hepdata.95230.v1/t13

    Distributions of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ in 30-50% centrality PbPb collisions at 5.02 TeV.

  • Table 14

    Data from top panel of Fig. 2

    10.17182/hepdata.95230.v1/t14

    Distributions of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ in 0-30% centrality PbPb collisions at 5.02 TeV.

  • Table 15

    Data from bottom panel of Fig. 2

    10.17182/hepdata.95230.v1/t15

    PbPb / pp ratio of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ distributions for 70-90% centrality PbPb collisions at 5.02 TeV.

  • Table 16

    Data from bottom panel of Fig. 2

    10.17182/hepdata.95230.v1/t16

    PbPb / pp ratio of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ distributions for 50-70% centrality PbPb collisions at 5.02 TeV.

  • Table 17

    Data from bottom panel of Fig. 2

    10.17182/hepdata.95230.v1/t17

    PbPb / pp ratio of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ distributions for 30-50% centrality PbPb collisions at 5.02 TeV.

  • Table 18

    Data from bottom panel of Fig. 2

    10.17182/hepdata.95230.v1/t18

    PbPb / pp ratio of $\xi^{\mathrm{trk,Z}}_{\mathrm{T}}$ distributions for 0-30% centrality PbPb collisions at 5.02 TeV.

  • Table 19

    Data from top left panel of Fig. 3

    10.17182/hepdata.95230.v1/t19

    Distributions of p$^{\mathrm{trk}}_{\mathrm{T}}$ in pp collisions at 5.02 TeV.

  • Table 20

    Data from top right panel of Fig. 3

    10.17182/hepdata.95230.v1/t20

    Distributions of p$^{\mathrm{trk}}_{\mathrm{T}}$ in pp collisions at 5.02 TeV.

  • Table 21

    Data from top panel of Fig. 3

    10.17182/hepdata.95230.v1/t21

    Distributions of p$^{\mathrm{trk}}_{\mathrm{T}}$ in 70-90% centrality PbPb collisions at 5.02 TeV.

  • Table 22

    Data from top panel of Fig. 3

    10.17182/hepdata.95230.v1/t22

    Distributions of p$^{\mathrm{trk}}_{\mathrm{T}}$ in 50-70% centrality PbPb collisions at 5.02 TeV.

  • Table 23

    Data from top panel of Fig. 3

    10.17182/hepdata.95230.v1/t23

    Distributions of p$^{\mathrm{trk}}_{\mathrm{T}}$ in 30-50% centrality PbPb collisions at 5.02 TeV.

  • Table 24

    Data from top panel of Fig. 3

    10.17182/hepdata.95230.v1/t24

    Distributions of p$^{\mathrm{trk}}_{\mathrm{T}}$ in 0-30% centrality PbPb collisions at 5.02 TeV.

  • Table 25

    Data from bottom panel of Fig. 3

    10.17182/hepdata.95230.v1/t25

    PbPb / pp ratio of p$^{\mathrm{trk}}_{\mathrm{T}}$ distributions for 70-90% centrality PbPb collisions at 5.02 TeV.

  • Table 26

    Data from bottom panel of Fig. 3

    10.17182/hepdata.95230.v1/t26

    PbPb / pp ratio of p$^{\mathrm{trk}}_{\mathrm{T}}$ distributions for 50-70% centrality PbPb collisions at 5.02 TeV.

  • Table 27

    Data from bottom panel of Fig. 3

    10.17182/hepdata.95230.v1/t27

    PbPb / pp ratio of p$^{\mathrm{trk}}_{\mathrm{T}}$ distributions for 30-50% centrality PbPb collisions at 5.02 TeV.

  • Table 28

    Data from bottom panel of Fig. 3

    10.17182/hepdata.95230.v1/t28

    PbPb / pp ratio of p$^{\mathrm{trk}}_{\mathrm{T}}$ distributions for 0-30% centrality PbPb collisions at 5.02 TeV.

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