Abstract (data abstract)

This Letter presents the first measurements of the groomed jet radius $R_{\mathrm{g}}$ and the jet girth $g$ in events with an isolated photon recoiling against a jet in lead-lead (PbPb) and proton-proton (pp) collisions at the LHC at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The observables $R_{\mathrm{g}}$ and $g$ provide a quantitative measure of how narrow or broad a jet is. The analysis uses PbPb and pp data samples with integrated luminosities of 1.7~nb$^{-1}$ and 301~pb$^{-1}$, respectively, collected with the CMS experiment in 2018 and 2017. Events are required to have a photon with transverse momentum $p_{\mathrm{T}}^{\gamma} > 100$~GeV and at least one jet back-to-back in azimuth with respect to the photon and with transverse momentum $p_{\mathrm{T}}^{\text{jet}}$ such that $p_{\mathrm{T}}^{\text{jet}}/p_{\mathrm{T}}^{\gamma} > 0.4$. The measured $R_{\mathrm{g}}$ and $g$ distributions are unfolded to the particle level, which facilitates the comparison between the PbPb and pp results and with theoretical predictions. It is found that jets with $p_{\mathrm{T}}^{\text{jet}}/p_{\mathrm{T}}^{\gamma} > 0.8$, i.e, those that closely balance the photon $p_{\mathrm{T}}^{\gamma}$, are narrower in PbPb than in pp collisions. Relaxing the selection to include jets with $p_{\mathrm{T}}^{\text{jet}}/p_{\mathrm{T}}^{\gamma} > 0.4$ reduces the narrowing of the angular structure of jets in PbPb relative to the pp reference. This shows that selection bias effects associated with jet energy loss play an important role in the interpretation of jet substructure measurements.

Normalized PbPb Jet girth for $x_J$>0.4

Corresponds to Figure 4 (left) in the paper.

10.17182/hepdata.151507.v1/t1

Unfolded jet girth distribution in PbPb normalized to the number of jets that pass the $x_J$>0.4 selection. All systematic uncertainties...
Data stats covariance matrix for girth for $x_J$>0.4

Associated to Figure 4 (left) in the paper.

10.17182/hepdata.151507.v1/t2

Covariance matrix of the statistical uncertainty in data for the unfolded jet girth distribution in PbPb for jets that pass...
MC stats covariance matrix for girth for $x_J$>0.4

Associated to Figure 4 (left) in the paper.

10.17182/hepdata.151507.v1/t3

Covariance matrix of the statistical uncertainty in MC for the unfolded jet girth distribution in PbPb for jets that pass...
Normalized PbPb Groomed jet radius $R_g$ for $x_J$>0.4

Corresponds to Figure 4 (right) in the paper.

10.17182/hepdata.151507.v1/t4

Unfolded groomed jet radius distribution in PbPb normalized to the number of jets that pass the $x_J$>0.4 selection. All systematic...
Data stats covariance matrix for $R_g$ for $x_J$>0.4

Associated to Figure 4 (right) in the paper.

10.17182/hepdata.151507.v1/t5

Covariance matrix of the statistical uncertainty in data for the unfolded groomed jet radius distribution in PbPb for jets that...
MC stats covariance matrix for $R_g$ for $x_J$>0.4

Associated to Figure 4 (right) in the paper.

10.17182/hepdata.151507.v1/t6

Covariance matrix of the statistical uncertainty in MC for the unfolded groomed jet radius distribution in PbPb for jets that...
Normalized PbPb Jet girth for $x_J$>0.8

Corresponds to Figure 5 (left) in the paper.

10.17182/hepdata.151507.v1/t7

Unfolded jet girth distribution in PbPb normalized to the number of jets that pass the $x_J$>0.8 selection. All systematic uncertainties...
Data stats covariance matrix for girth for $x_J$>0.8

Associated to Figure 5 (left) in the paper.

10.17182/hepdata.151507.v1/t8

Covariance matrix of the statistical uncertainty in data for the unfolded jet girth distribution in PbPb for jets that pass...
MC stats covariance matrix for girth for $x_J$>0.8

Associated to Figure 5 (left) in the paper.

10.17182/hepdata.151507.v1/t9

Covariance matrix of the statistical uncertainty in MC for the unfolded jet girth distribution in PbPb for jets that pass...
Normalized PbPb Groomed jet radius $R_g$ for $x_J$>0.8

Corresponds to Figure 5 (right) in the paper.

10.17182/hepdata.151507.v1/t10

Unfolded groomed jet radius distribution in PbPb normalized to the number of jets that pass the $x_J$>0.8 selection. All systematic...
Data stats covariance matrix for $R_g$ for $x_J$>0.8

Associated to Figure 5 (right) in the paper.

10.17182/hepdata.151507.v1/t11

Covariance matrix of the statistical uncertainty in data for the unfolded groomed jet radius distribution in PbPb for jets that...
MC stats covariance matrix for $R_g$ for $x_J$>0.8

Associated to Figure 5 (right) in the paper.

10.17182/hepdata.151507.v1/t12

Covariance matrix of the statistical uncertainty in MC for the unfolded groomed jet radius distribution in PbPb for jets that...
Normalized pp Jet girth for $x_J$>0.4

Corresponds to Figures 2 and 4 (left) in the paper.

10.17182/hepdata.151507.v1/t13

Unfolded jet girth distribution in pp normalized to the number of jets that pass the $x_J$>0.4 selection. All systematic uncertainties...
pp Data stats covariance matrix for girth for $x_J$>0.4

Associated to Figures 2 and 4 (left) in the paper.

10.17182/hepdata.151507.v1/t14

Covariance matrix of the statistical uncertainty in data for the unfolded jet girth distribution in pp for jets that pass...
pp MC stats covariance matrix for girth for $x_J$>0.4

Associated to Figures 2 and 4 (left) in the paper.

10.17182/hepdata.151507.v1/t15

Covariance matrix of the statistical uncertainty in MC for the unfolded jet girth distribution in pp for jets that pass...
Normalized pp Groomed jet radius $R_g$ for $x_J$>0.4

Corresponds to Figures 2 and 4 (right) in the paper.

10.17182/hepdata.151507.v1/t16

Unfolded groomed jet radius distribution in pp normalized to the number of jets that pass the $x_J$>0.4 selection. All systematic...
pp Data stats covariance matrix for $R_g$ for $x_J$>0.4

Associated to Figures 2 and 4 (right) in the paper.

10.17182/hepdata.151507.v1/t17

Covariance matrix of the statistical uncertainty in data for the unfolded groomed jet radius distribution in pp for jets that...
pp MC stats covariance matrix for $R_g$ for $x_J$>0.4

Associated to Figures 2 and 4 (right) in the paper.

10.17182/hepdata.151507.v1/t18

Covariance matrix of the statistical uncertainty in MC for the unfolded groomed jet radius distribution in pp for jets that...
Normalized pp Jet girth for $x_J$>0.8

Corresponds to Figures 3 and 5 (left) in the paper.

10.17182/hepdata.151507.v1/t19

Unfolded jet girth distribution in pp normalized to the number of jets that pass the $x_J$>0.8 selection. All systematic uncertainties...
pp Data stats covariance matrix for girth for $x_J$>0.8

Associated to Figures 3 and 5 (left) in the paper.

10.17182/hepdata.151507.v1/t20

Covariance matrix of the statistical uncertainty in data for the unfolded jet girth distribution in pp for jets that pass...
pp MC stats covariance matrix for girth for $x_J$>0.8

Associated to Figures 3 and 5 (left) in the paper.

10.17182/hepdata.151507.v1/t21

Covariance matrix of the statistical uncertainty in MC for the unfolded jet girth distribution in pp for jets that pass...
Normalized pp Groomed jet radius $R_g$ for $x_J$>0.8

Corresponds to Figures 3 and 5 (right) in the paper.

10.17182/hepdata.151507.v1/t22

Unfolded groomed jet radius distribution in pp normalized to the number of jets that pass the $x_J$>0.8 selection. All systematic...
pp Data stats covariance matrix for $R_g$ for $x_J$>0.8

Associated to Figures 3 and 5 (right) in the paper.

10.17182/hepdata.151507.v1/t23

Covariance matrix of the statistical uncertainty in data for the unfolded groomed jet radius distribution in pp for jets that...
pp MC stats covariance matrix for $R_g$ for $x_J$>0.8

Associated to Figures 3 and 5 (right) in the paper.

10.17182/hepdata.151507.v1/t24

Covariance matrix of the statistical uncertainty in MC for the unfolded groomed jet radius distribution in pp for jets that...
Ratio of yields for Jet girth for $x_J$>0.4

Corresponds to Figure 6 (left) in the paper.

10.17182/hepdata.151507.v1/t25

Ratio of yields in PbPb to pp for the unfolded jet girth distribution normalized to the number of jets that...
Ratio of yields for Groomed jet radius $R_g$ for $x_J$>0.4

Corresponds to Figure 6 (right) in the paper.

10.17182/hepdata.151507.v1/t26

Ratio of yields in PbPb to pp for the unfolded groomed jet radius distribution normalized to the number of jets...
Ratio of yields for Jet girth for $x_J$>0.8

Corresponds to Figure 7 (left) in the paper.

10.17182/hepdata.151507.v1/t27

Ratio of yields in PbPb to pp for the unfolded jet girth distribution normalized to the number of jets that...
Ratio of yields for Groomed jet radius $R_g$ for $x_J$>0.8

Corresponds to Figure 7 (right) in the paper.

10.17182/hepdata.151507.v1/t28

Ratio of yields in PbPb to pp for the unfolded groomed jet radius distribution normalized to the number of jets...

Normalized PbPb Jet girth for $x_J$>0.4

Data stats covariance matrix for girth for $x_J$>0.4

MC stats covariance matrix for girth for $x_J$>0.4

Normalized PbPb Groomed jet radius $R_g$ for $x_J$>0.4

Data stats covariance matrix for $R_g$ for $x_J$>0.4

MC stats covariance matrix for $R_g$ for $x_J$>0.4

Normalized PbPb Jet girth for $x_J$>0.8

Data stats covariance matrix for girth for $x_J$>0.8

MC stats covariance matrix for girth for $x_J$>0.8

Normalized PbPb Groomed jet radius $R_g$ for $x_J$>0.8

Data stats covariance matrix for $R_g$ for $x_J$>0.8

MC stats covariance matrix for $R_g$ for $x_J$>0.8

Normalized pp Jet girth for $x_J$>0.4

pp Data stats covariance matrix for girth for $x_J$>0.4

pp MC stats covariance matrix for girth for $x_J$>0.4

Normalized pp Groomed jet radius $R_g$ for $x_J$>0.4

pp Data stats covariance matrix for $R_g$ for $x_J$>0.4

pp MC stats covariance matrix for $R_g$ for $x_J$>0.4

Normalized pp Jet girth for $x_J$>0.8

pp Data stats covariance matrix for girth for $x_J$>0.8

pp MC stats covariance matrix for girth for $x_J$>0.8

Normalized pp Groomed jet radius $R_g$ for $x_J$>0.8

pp Data stats covariance matrix for $R_g$ for $x_J$>0.8

pp MC stats covariance matrix for $R_g$ for $x_J$>0.8

Ratio of yields for Jet girth for $x_J$>0.4

Ratio of yields for Groomed jet radius $R_g$ for $x_J$>0.4

Ratio of yields for Jet girth for $x_J$>0.8

Ratio of yields for Groomed jet radius $R_g$ for $x_J$>0.8

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