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CMS-SMP-23-007 ; CERN-EP-2026-099
Measurement of the $ \mathrm{Z} \to \mu^{+}\mu^{-} $ angular coefficients in pp collisions at $ \sqrt{s} = $ 13 TeV as functions of transverse momentum and rapidity
Submitted to Physics Letters B
Abstract: A measurement of the eight angular polarization coefficients, $ A_0 $ to $ A_7 $, in the cross section for the Drell--Yan production of two muons is presented. The analysis is based on proton-proton (pp) collision data recorded with the CMS detector at the LHC at a center-of-mass energy of $ \sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 140 fb$ ^{-1} $. The coefficients are determined double differentially in eight intervals of transverse momentum and two intervals of rapidity of the muon pair $ \mu^{+}\mu^{-} $. The results are presented for the $ \mu^{+}\mu^{-} $ invariant mass range 81--101 GeV and are compared with theoretical predictions calculated at next-to-next-to-leading order in perturbative quantum chromodynamics. The measurement provides relevant information about the underlying partonic dynamics and the Z boson production mechanisms.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
The definition of the CS frame and angles $ \phi^* $ and $ \theta^* $ of the negatively charged lepton produced in the ${\gamma}^{*} /\mathrm{Z} $ decay. The $ p_1 $ and $ p_2 $ vectors indicate the directions of the incoming proton's momenta in the dilepton rest frame and $ \ell $ indicates the momentum of the negatively charged lepton [10].

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Figure 2:
Distributions of events as functions of $ \cos{\theta^*} $ (left) and $ \phi^* $ (right), averaged over $ p_{\mathrm{T}}^{\mu\mu} $ and $ y^{\mu\mu} $. The measured distributions are represented by the black markers. The simulated contributions (from the signal and background processes) are shown by the colored histograms. The data/MC ratios are presented in the lower panels. The gray bands around unity represent the total systematic uncertainties.

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Figure 2-a:
Distributions of events as functions of $ \cos{\theta^*} $ (left) and $ \phi^* $ (right), averaged over $ p_{\mathrm{T}}^{\mu\mu} $ and $ y^{\mu\mu} $. The measured distributions are represented by the black markers. The simulated contributions (from the signal and background processes) are shown by the colored histograms. The data/MC ratios are presented in the lower panels. The gray bands around unity represent the total systematic uncertainties.

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Figure 2-b:
Distributions of events as functions of $ \cos{\theta^*} $ (left) and $ \phi^* $ (right), averaged over $ p_{\mathrm{T}}^{\mu\mu} $ and $ y^{\mu\mu} $. The measured distributions are represented by the black markers. The simulated contributions (from the signal and background processes) are shown by the colored histograms. The data/MC ratios are presented in the lower panels. The gray bands around unity represent the total systematic uncertainties.

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Figure 3:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-a:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-b:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-c:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-d:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-e:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-f:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-g:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 3-h:
Left: Polarization coefficients $ A_{0} $ to $ A_{3} $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1. The data points are shown as black circles. The POWHEG+MINNLO and the MadGraph-5_aMC@NLO predictions are represented by the red circles and blue squares, respectively, slightly displaced horizontally for improved visibility. The vertical bars (hatched boxes) represent the statistical (systematic) uncertainties. Right: Difference between the predicted and measured values. The gray area around zero represents the total uncertainty of the measurement, while the vertical bars represent the statistical uncertainties of the predictions.

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Figure 4:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-a:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-b:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-c:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-d:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-e:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-f:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-g:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 4-h:
Same as Fig. 3, for the polarization coefficients $ A_4 $ to $ A_7 $.

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Figure 5:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-a:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-b:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-c:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-d:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-e:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-f:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-g:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 5-h:
Same as Fig. 3, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-a:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-b:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-c:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-d:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-e:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-f:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-g:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 6-h:
Same as Fig. 4, for the 1 $ < |y^{\mu\mu}| < $ 2.4 bin.

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Figure 7:
Left: Difference $ A_0-A_2 $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1 (upper) and 1 $ < |y^{\mu\mu}| < $ 2.4 (lower). Right: Corresponding differences between the predicted and measured values.

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Figure 7-a:
Left: Difference $ A_0-A_2 $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1 (upper) and 1 $ < |y^{\mu\mu}| < $ 2.4 (lower). Right: Corresponding differences between the predicted and measured values.

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Figure 7-b:
Left: Difference $ A_0-A_2 $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1 (upper) and 1 $ < |y^{\mu\mu}| < $ 2.4 (lower). Right: Corresponding differences between the predicted and measured values.

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Figure 7-c:
Left: Difference $ A_0-A_2 $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1 (upper) and 1 $ < |y^{\mu\mu}| < $ 2.4 (lower). Right: Corresponding differences between the predicted and measured values.

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Figure 7-d:
Left: Difference $ A_0-A_2 $ measured in the CS frame in bins of $ p_{\mathrm{T}}^{\mu\mu} $ for $ |y^{\mu\mu}| < $ 1 (upper) and 1 $ < |y^{\mu\mu}| < $ 2.4 (lower). Right: Corresponding differences between the predicted and measured values.
Tables

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Table A1:
Measured angular coefficients, in bins of $ p_{\mathrm{T}}^{\mu\mu} $ (in GeV), for $ |y^{\mu\mu}| < $ 1.

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Table A2:
Measured angular coefficients, in bins of $ p_{\mathrm{T}}^{\mu\mu} $ (in GeV), for 1 $ < |y^{\mu\mu}| < $ 2.4.

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Table A3:
Measured $ A_0-A_2 $ difference in bins of $ p_{\mathrm{T}}^{\mu\mu} $ (in GeV) and $ |y^{\mu\mu}| $.
Summary
The first measurement of the full set of angular polarization coefficients $ A_0 $--$ A_7 $ in the Drell--Yan dimuon channel in the central rapidity range 0 $ < |y^{\mu\mu}| < $ 2.4 and $ p_{\mathrm{T}}^{\mu\mu} < $ 400 GeV at $ \sqrt{s}= $ 13 TeV is presented. The coefficients were determined double differentially in bins of transverse momentum and rapidity of the dimuon in the 81--101 GeV invariant mass range. The results are compared with state-of-the-art theoretical predictions at next-to-next-to-leading order in QCD and show consistency within uncertainties in most of the phase space. The presented results provide a comprehensive characterization of the angular structure of dilepton production and offer stringent constraints on theoretical descriptions of electroweak vector boson production mechanisms and underlying partonic dynamics [5,6]. The achieved precision and multidimensional binning establish a valuable benchmark for future phenomenological studies and for testing higher-order calculations [19,20]. With larger data sets and simulated event samples, more precise measurements will be possible in the high transverse momentum region, where the contribution of QCD higher-order effects is still poorly studied. Improved modeling of the detector system response will reduce the systematic uncertainty of the measurement.
References
1 S. D. Drell and T.-M. Yan Massive lepton pair production in hadron-hadron collisions at high-energies PRL 25 (1970) 316
2 E. Mirkes and J. Ohnemus W and Z polarization effects in hadronic collisions PRD 50 (1994) 5692 hep-ph/9406381
3 E. Mirkes Angular decay distribution of leptons from W-bosons at NLO in hadronic collisions NPB 387 (1992) 3
4 A. Bodek, J. Han, A. Khukhunaishvili, and W. Sakumoto Using Drell-Yan forward-backward asymmetry to reduce PDF uncertainties in the measurement of electroweak parameters EPJC 76 (2016) 115 1507.02470
5 B. Zhang, Z. Lu, B.-Q. Ma, and I. Schmidt Extracting Boer--Mulders functions from p+D Drell--Yan processes PRD 77 (2008) 054011 0803.1692
6 S. Piloneta and A. Vladimirov Angular distributions of Drell--Yan leptons in the TMD factorization approach JHEP 12 (2024) 059 2407.06277
7 J. C. Collins and D. E. Soper Angular distribution of dileptons in high-energy hadron collisions PRD 16 (1977) 2219
8 CMS Collaboration Angular coefficients of Z bosons produced in pp collisions at $ \sqrt{s} = 8 \textrm{TeV} $ and decaying to $ \mu^+ \mu^- $ as a function of transverse momentum and rapidity PLB 750 (2015) 154 CMS-SMP-13-010
1504.03512
9 ATLAS Collaboration Measurement of the angular coefficients in $ Z $-boson events using electron and muon pairs from data taken at $ \sqrt{s}= $ 8 TeV with the ATLAS detector JHEP 08 (2016) 159 1606.00689
10 R. Gauld et al. Precise predictions for the angular coefficients in Z-boson production at the LHC JHEP 11 (2017) 003 1708.00008
11 C. S. Lam and W.-K. Tung Systematic approach to inclusive lepton pair production in hadronic collisions PRD 18 (1978) 2447
12 P. Faccioli, C. Louren ç o, and J. Seixas Rotation-invariant relations in vector meson decays into fermion pairs PRL 105 (2010) 061601 1005.2601
13 P. Faccioli and C. Lourenço Particle polarization in high energy physics: an introduction and case studies on vector particle production at the LHC Lecture Notes in Physics. Springer, 2022
link
14 J.-C. Peng, W.-C. Chang, R. E. McClellan, and O. Teryaev Interpretation of angular distributions of Z-boson production at colliders PLB 758 (2016) 384 1511.08932
15 D. Boer Intrinsic transverse momentum and transverse spin asymmetries Nucl. Phys. B Proc. Suppl. 79 (1999) 638 hep-ph/9905336
16 CDF Collaboration Indirect measurement of $ \sin^2\theta_{\mathrm{W}}(M_{\mathrm{W}}) $ using $ \mathrm{e}^+\mathrm{e}^- $ pairs in the Z-boson region with $ \mathrm{p}\overline{\mathrm{p}} $ collisions at a center-of-momentum energy of 1.96 TeV PRD 88 (2013) 072002 1307.0770
17 CDF Collaboration First measurement of the angular coefficients of Drell--Yan $ \mathrm{e}^{+}\mathrm{e}^{-} $ pairs in the Z mass region from $ \mathrm{p}\overline{\mathrm{p}} $ collisions at $ \sqrt{s} = $ 1.96 TeV PRL 106 (2011) 241801 1103.5699
18 CMS Collaboration Measurement of the Drell--Yan forward-backward asymmetry and of the effective leptonic weak mixing angle in proton-proton collisions at $ \sqrt{s} = $ 13 TeV PLB 866 (2025) 139526 CMS-SMP-22-010
2408.07622
19 K. Hagiwara, K.-i. Hikasa, and N. Kai Time-reversal-odd asymmetry in semi-inclusive lepton production in Quantum Chromodynamics PRD 27 (1983) 84
20 K. Hagiwara, T. Kuruma, and Y. Yamada Probing the one-loop Zgg vertex at hadron colliders NPB 369 (1992) 171
21 LHCb Collaboration First measurement of the $ \mathrm{Z}\to\mu^{+}\mu^{-} $ angular coefficients in the forward region of pp collisions at $ \sqrt{s}= $ 13 TeV PRL 129 (2022) 091801 2203.01602
22 CMS Collaboration HEPData record for this analysis link
23 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004
24 CMS Collaboration Performance of the CMS Level-1 trigger in proton-proton collisions at $ \sqrt{s} = $ 13 TeV JINST 15 (2020) P10017 CMS-TRG-17-001
2006.10165
25 CMS Collaboration The CMS trigger system JINST 12 (2017) P01020 CMS-TRG-12-001
1609.02366
26 CMS Collaboration Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC JINST 16 (2021) P05014 CMS-EGM-17-001
2012.06888
27 CMS Collaboration Performance of the CMS muon detector and muon reconstruction with proton-proton collisions at $ \sqrt{s}= $ 13 TeV JINST 13 (2018) P06015 CMS-MUO-16-001
1804.04528
28 CMS Collaboration Description and performance of track and primary-vertex reconstruction with the CMS tracker JINST 9 (2014) P10009 CMS-TRK-11-001
1405.6569
29 CMS Collaboration Particle-flow reconstruction and global event description with the CMS detector JINST 12 (2017) P10003 CMS-PRF-14-001
1706.04965
30 CMS Collaboration Performance of the CMS high-level trigger during LHC Run 2 JINST 19 (2024) P11021 CMS-TRG-19-001
2410.17038
31 P. F. Monni et al. MiNNLO$ _{\mathrm{PS}} $: a new method to match NNLO QCD to parton showers JHEP 05 (2020) 143 1908.06987
32 S. Frixione, P. Nason, and C. Oleari Matching NLO QCD computations with Parton Shower simulations: the POWHEG method JHEP 11 (2007) 070 0709.2092
33 T. Sjöstrand et al. An introduction to PYTHIA 8.2 Comput. Phys. Commun. 191 (2015) 159 1410.3012
34 N. Davidson, T. Przedzinski, and Z. Was PHOTOS interface in C++: technical and physics documentation Comput. Phys. Commun. 199 (2016) 86 1011.0937
35 NNPDF Collaboration Parton distributions from high-precision collider data EPJC 77 (2017) 663 1706.00428
36 J. Alwall et al. The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations JHEP 07 (2014) 079 1405.0301
37 R. Frederix and S. Frixione Merging meets matching in MC@NLO JHEP 12 (2012) 061 1209.6215
38 CMS Collaboration Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements EPJC 80 (2020) 4 CMS-GEN-17-001
1903.12179
39 CMS Collaboration Measurements of differential Z boson production cross sections in proton-proton collisions at $ \sqrt{s} = $ 13 TeV JHEP 12 (2019) 061 CMS-SMP-17-010
1909.04133
40 S. Agostinelli et al. GEANT4--A simulation toolkit NIM A 506 (2003) 250
41 A. Bodek et al. Extracting muon momentum scale corrections for hadron collider experiments EPJC 72 (2012) 2194 1208.3710
42 CMS Collaboration Performance of the CMS muon trigger system in proton-proton collisions at $ \sqrt{s} = $ 13 TeV JINST 16 (2021) P07001 CMS-MUO-19-001
2102.04790
43 F. James MINUIT function minimization and error analysis: reference manual version 94.1 Technical report, CERN, 1994
link
44 CMS Collaboration Precision luminosity measurement in proton-proton collisions at $ \sqrt{s} = $ 13 TeV in 2015 and 2016 at CMS EPJC 81 (2021) 800 CMS-LUM-17-003
2104.01927
45 CMS Collaboration Precision luminosity measurement in proton-proton collisions at $ \sqrt{s} = $ 13 TeV with the CMS detector Technical Report, CERN, 2025
CMS-PAS-LUM-20-001
CMS-PAS-LUM-20-001
46 J. Butterworth et al. PDF4LHC recommendations for LHC Run II JPG 43 (2016) 023001 1510.03865
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