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

The 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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