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CMS-HIN-24-001 ; CERN-EP-2024-332
Observation of the charged-particle multiplicity dependence of $ \sigma_{\psi(2\text{S})} /\sigma_{\mathrm{J}/\psi} $ in pPb collisions at 8.16 TeV
Submitted to Phys. Rev. Lett.
Abstract: Bound states of charm and anticharm quarks, known as charmonia, have a rich spectroscopic structure that can be used to probe the dynamics of hadron production in high-energy hadron collisions. Here, the cross section ratio of excited $ (\psi(2\text{S})) $ and ground state $ (\mathrm{J}/\psi ) $ vector mesons is measured as a function of the charged-particle multiplicity in proton-lead (pPb ) collisions at a center-of-mass (CM) energy per nucleon pair of 8.16 TeV. The data corresponding to an integrated luminosity of 175 nb$^{-1}$ were collected using the CMS detector. The ratio is measured separately for prompt and nonprompt charmonia in the transverse momentum range 6.5 $ < p_{\mathrm{T}} < $ 30 GeV and in four rapidity ranges spanning $ -$2.865 $< y_{\mathrm{CM}} < $ 1.935. For the first time, a statistically significant multiplicity dependence of the prompt cross section ratio is observed in proton-nucleus collisions. There is no clear rapidity dependence in the ratio. The prompt measurements are compared with a theoretical model which includes interactions with nearby particles during the evolution of the system. These results provide additional constraints on hadronization models of heavy quarks in nuclear collisions.
Figures Summary References CMS Publications
Figures

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Figure 1:
The prompt (red circular points) and nonprompt (blue square points) normalized cross section ratio for $ -$2.865 $< y_{\mathrm{CM}} < - $2 (the leftmost), $ -$2 $< y_{\mathrm{CM}} < - $1 (center-left), $ -$1 $< y_{\mathrm{CM}} < $ 1 (center-right), and 1 $ < y_{\mathrm{CM}} < $ 1.935 (the rightmost) in the range 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. The black line with a gray band shows a model incorporating co-mover effects [50] for prompt charmonia. Error bars represent statistical uncertainties, while boxes display systematic uncertainties.

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Figure 2:
(upper) The prompt normalized cross section ratio versus normalized event charged-particle multiplicity for four different rapidity selections. The different sets of colored data points have a slight horizontal offset applied for visual clarity. (lower) The same observable for prompt (red circular points) and nonprompt (blue square points) mesons when combining all four rapidity selections into a single measurement. The black line with a gray band shows a model incorporating co-mover effects [50] for prompt charmonia. Error bars represent statistical uncertainties, while boxes display systematic uncertainties.

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Figure 3:
Dimuon invariant mass distribution showing the $ \mathrm{J}/\psi $ and $\psi(2\text{S})$ peaks in pPb data, for $ -$2.865 $< y_{\mathrm{CM}} < - $2 (left) and 1 $ < y_{\mathrm{CM}} < $ 1.935 (right) for 3 $ < p_{\mathrm{T}} < $ 30 GeV. The total fit is shown with a solid blue line, and the dotted blue line represents the background contribution.

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Figure 3-a:
Dimuon invariant mass distribution showing the $ \mathrm{J}/\psi $ and $\psi(2\text{S})$ peaks in pPb data, for $ -$2.865 $< y_{\mathrm{CM}} < - $2 (left) and 1 $ < y_{\mathrm{CM}} < $ 1.935 (right) for 3 $ < p_{\mathrm{T}} < $ 30 GeV. The total fit is shown with a solid blue line, and the dotted blue line represents the background contribution.

png pdf
Figure 3-b:
Dimuon invariant mass distribution showing the $ \mathrm{J}/\psi $ and $\psi(2\text{S})$ peaks in pPb data, for $ -$2.865 $< y_{\mathrm{CM}} < - $2 (left) and 1 $ < y_{\mathrm{CM}} < $ 1.935 (right) for 3 $ < p_{\mathrm{T}} < $ 30 GeV. The total fit is shown with a solid blue line, and the dotted blue line represents the background contribution.

png pdf
Figure 4:
The prompt (red circular points) and nonprompt (blue square points) normalized cross section ratio for $ -$2.865 $< y_{\mathrm{CM}} < - $2 (upper), and 1 $ < y_{\mathrm{CM}} < $ 1.935 (lower) in the range 3 $ < p_{\mathrm{T}} < $ 6.5 GeV. Error bars represent statistical uncertainties, while boxes display systematic uncertainties.
Summary
In summary, this Letter presents a measurement of the normalized production cross section ratio of $\psi(2\text{S})$ over $ \mathrm{J}/\psi $ mesons as a function of charged-particle multiplicity in proton-lead collisions at a center-of-mass energy per nucleon pair of 8.16 TeV with a data sample collected with the CMS detector. The ratio is measured for both prompt and nonprompt $\psi(2\text{S})$ and $ \mathrm{J}/\psi $ mesons separately. For the first time in proton-ion collisions, a statistically significant multiplicity-dependent modification of the ratio is observed for prompt charmonia, indicating a decreasing trend with increasing multiplicity. The ratio of the nonprompt cross sections shows no dependency on the multiplicity. No appreciable rapidity dependence is observed within the charmonium rapidity and transverse momentum ranges probed. These observations support the presence of final state effects dissociating weakly bound excited states of charmonia more than the ground state, which can be interpreted as co-mover dissociation or, potentially, the formation of quark-gluon plasma. These new data provide powerful tests for hadronization models in small collision systems.
References
1 W. Busza, K. Rajagopal, and W. van der Schee Heavy ion collisions: The big picture, and the big questions Ann. Rev. Nucl. Part. Sci. 68 (2018) 339 1802.04801
2 CMS Collaboration Overview of high-density QCD studies with the CMS experiment at the LHC Accepted by Physics Reports, 2024 CMS-HIN-23-011
2405.10785
3 ALICE Collaboration The ALICE experiment: a journey through QCD EPJC 84 (2024) 813 2211.04384
4 G. T. Bodwin, E. Braaten, and G. P. Lepage Rigorous QCD analysis of inclusive annihilation and production of heavy quarkonium PRD 51 (1995) 1125 hep-ph/9407339
5 T. Matsui and H. Satz $ \text{J}/\psi $ suppression by quark-gluon plasma formation PLB 178 (1986) 416
6 F. Karsch, M. T. Mehr, and H. Satz Color screening and deconfinement for bound states of heavy quarks Z. Phys. C 37 (1988) 617
7 D. Kharzeev and H. Satz Quarkonium interactions in hadronic matter PLB 334 (1994) 155 hep-ph/9405414
8 M. Laine, O. Philipsen, P. Romatschke, and M. Tassler Real-time static potential in hot QCD JHEP 03 (2007) 054 hep-ph/0611300
9 N. Brambilla, J. Ghiglieri, A. Vairo, and P. Petreczky Static quark-antiquark pairs at finite temperature PRD 78 (2008) 014017 0804.0993
10 N. Brambilla et al. Heavy quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature JHEP 09 (2010) 038 1007.4156
11 J.-P. Blaizot, D. De Boni, P. Faccioli, and G. Garberoglio Heavy quark bound states in a quark-gluon plasma: Dissociation and recombination Nucl. Phys. A 946 (2016) 49 1503.03857
12 H. van Hees, V. Greco, and R. Rapp Heavy-quark probes of the quark-gluon plasma at RHIC Phys. Rev. C 73 (2006) 034913 nucl-th/0508055
13 N. Brambilla et al. Bottomonium production in heavy-ion collisions using quantum trajectories: Differential observables and momentum anisotropy PRD 104 (2021) 094049 2107.06222
14 X. Yao et al. Coupled boltzmann transport equations of heavy quarks and quarkonia in quark-gluon plasma JHEP 01 (2021) 046 2004.06746
15 X. Du, M. He, and R. Rapp Color screening and regeneration of bottomonia in high-energy heavy-ion collisions Phys. Rev. C 96 (2017) 054901 1706.08670
16 R. L. Thews, M. Schroedter, and J. Rafelski Enhanced $ \text{J}/\psi $ production in deconfined quark matter Phys. Rev. C 63 (2001) 054905 hep-ph/0007323
17 P. Braun-Munzinger and J. Stachel (Non)thermal aspects of charmonium production and a new look at $ \text{J}/\psi $ suppression PLB 490 (2000) 196 nucl-th/0007059
18 N. Brambilla, M. A. Escobedo, J. Soto, and A. Vairo Quarkonium suppression in heavy-ion collisions: an open quantum system approach PRD 96 (2017) 034021 1612.07248
19 A. Emerick, X. Zhao, and R. Rapp Bottomonia in the quark-gluon plasma and their production at RHIC and LHC Eur. Phys. J. A 48 (2012) 72 1111.6537
20 NA38 Collaboration $ \psi^{\prime} $ and $ \text{J}/\psi $ production in p--W, p--U and S--U interactions at 200 GeV/nucleon PLB 345 (1995) 617
21 NA50 Collaboration $ \text{J}/\psi $ and $ \psi^{\prime} $ production and their normal nuclear absorption in proton-nucleus collisions at 400 GeV EPJC 48 (2006) 329 nucl-ex/0612012
22 NA50 Collaboration Charmonium production and nuclear absorption in p-A interactions at 450 GeV EPJC 33 (2004) 31
23 NA51 Collaboration $ \text{J}/\psi $, $ \psi^{\prime} $ and Drell-Yan production in pp and pd interactions at 450 GeV/c PLB 438 (1998) 35
24 NA60 Collaboration $ \text{J}/\psi $ production in proton-nucleus collisions at 158 and 400 GeV PLB 706 (2012) 263 1004.5523
25 D. M. Alde et al. $ A $ dependence of $ \text{J}/\psi $ and $ \psi^{\prime} $ production at 800 GeV/c PRL 66 (1991) 133
26 NuSea Collaboration Measurement of $ \text{J}/\psi $ and $ \psi^{\prime} $ suppression in p--A collisions at 800 GeV/c PRL 84 (2000) 3256 nucl-ex/9909007
27 SeaQuest Collaboration Measurement of $ \text{J}/\psi $ and $ \psi $ (2S) production in $ {\mathrm{p}}+{\mathrm{p}} $ and $ {\mathrm{p}}+\mathrm{d} $ interactions at 120 GeV PLB 858 (2024) 139032 2406.11459
28 HERA-B Collaboration Kinematic distributions and nuclear effects of $ \text{J}/\psi $ production in 920 GeV fixed-target proton-nucleus collisions EPJC 60 (2009) 525 0812.0734
29 PHENIX Collaboration Measurement of $ \text{J}/\psi $ at forward and backward rapidity in $ {\mathrm{p}}+{\mathrm{p}} $, $ {\mathrm{p}}+\mathrm{Al} $, $ {\mathrm{p}}+\mathrm{Au} $, and $ ^{3}\mathrm{He}+\mathrm{Au} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 200 GeV Phys. Rev. C 102 (2020) 014902 1910.14487
30 PHENIX Collaboration Measurement of $ \psi $ (2S) nuclear modification at backward and forward rapidity in $ {\mathrm{p}}+{\mathrm{p}} $, $ {\mathrm{p}}+\mathrm{Al} $, and $ {\mathrm{p}}+\mathrm{Au} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 200 GeV Phys. Rev. C 105 (2022) 064912 2202.03863
31 STAR Collaboration Measurement of cold nuclear matter effects for inclusive $ \text{J}/\psi $ in $ {\mathrm{p}}+\mathrm{Au} $ collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 200 GeV PLB 825 (2022) 136865 2110.09666
32 CMS Collaboration Measurement of prompt $ \psi $ (2S) $ \to \text{J}/\psi $ yield ratios in PbPb and pp collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 2.76 TeV PRL 113 (2014) 262301 CMS-HIN-12-007
1410.1804
33 CMS Collaboration Relative modification of prompt $ \psi $ (2S) and $ \text{J}/\psi $ yields from pp to PbPb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV PRL 118 (2017) 162301 CMS-HIN-16-004
1611.01438
34 CMS Collaboration Nuclear modification of $ \Upsilon $ states in $ \mathrm{p} $Pb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5.02 TeV PLB 835 (2022) 137397 CMS-HIN-18-005
2202.11807
35 CMS Collaboration Measurement of prompt $ \psi $ (2S) production cross sections in proton-lead and proton-proton collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV PLB 790 (2019) 509 CMS-HIN-16-015
1805.02248
36 CMS Collaboration Event activity dependence of $ \Upsilon $ (nS) production in $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV $ \mathrm{p} $Pb and $ \sqrt{s}= $ 2.76 TeV pp collisions JHEP 04 (2014) 103 CMS-HIN-13-003
1312.6300
37 CMS Collaboration Investigation into the event-activity dependence of $ \Upsilon $ (nS) relative production in proton-proton collisions at $ \sqrt{s}= $ 7 TeV JHEP 11 (2020) 001 CMS-BPH-14-009
2007.04277
38 LHCb Collaboration Study of $ \Upsilon $ production in $ \mathrm{p} $Pb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 8.16 TeV JHEP 11 (2018) 194 1810.07655
39 LHCb Collaboration Study of $ \psi $ (2S) production and cold nuclear matter effects in $ \mathrm{p} $Pb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 5 TeV JHEP 03 (2016) 133 1601.07878
40 ALICE Collaboration $ \Upsilon $ production in p--Pb and Pb--Pb collisions with ALICE at the LHC Nucl. Part. Phys. Proc. 289 (2017) 397 1612.06691
41 ALICE Collaboration Measurement of nuclear effects on $ \psi $ (2S) production in p--Pb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 8.16 TeV JHEP 07 (2020) 237 2003.06053
42 ATLAS Collaboration Measurement of quarkonium production in proton-lead and proton-proton collisions at 5.02 TeV with the ATLAS detector EPJC 78 (2018) 171 1709.03089
43 H. Khanpour and S. Atashbar Tehrani Global analysis of nuclear parton distribution functions and their uncertainties at next-to-next-to-leading order PRD 93 (2016) 014026 1601.00939
44 F. Arleo and S. Peign é Quarkonium suppression in heavy-ion collisions from coherent energy loss in cold nuclear matter JHEP 10 (2014) 073 1407.5054
45 C. Lourenco, R. Vogt, and H. K. Woehri Energy dependence of $ \text{J}/\psi $ absorption in proton-nucleus collisions JHEP 02 (2009) 014 0901.3054
46 J. L. Nagle and W. A. Zajc Small system collectivity in relativistic hadronic and nuclear collisions Ann. Rev. Nucl. Part. Sci. 68 (2018) 211 1801.03477
47 J. F. Grosse-Oetringhaus and U. A. Wiedemann A Decade of Collectivity in Small Systems 2407.07484
48 PHENIX Collaboration Creation of quark-gluon plasma droplets with three distinct geometries Nature Phys. 15 (2019) 214 1805.02973
49 E. G. Ferreiro Charmonium dissociation and recombination at LHC: Revisiting comovers PLB 731 (2014) 57 1210.3209
50 E. G. Ferreiro Excited charmonium suppression in proton-nucleus collisions as a consequence of comovers PLB 749 (2015) 98 1411.0549
51 ATLAS Collaboration Transverse momentum, rapidity, and centrality dependence of inclusive charged-particle production in $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV $ \mathrm{p}+\mathrm{Pb} $ collisions measured by the ATLAS experiment PLB 763 (2016) 313 1605.06436
52 X. Du and R. Rapp In-medium charmonium production in proton-nucleus collisions JHEP 03 (2019) 015 1808.10014
53 S. Gavin and R. Vogt Charmonium suppression by comover scattering in $ \mathrm{Pb}+\mathrm{Pb} $ collisions PRL 78 (1997) 1006 hep-ph/9606460
54 E. G. Ferreiro and J.-P. Lansberg Is bottomonium suppression in proton-nucleus and nucleus-nucleus collisions at LHC energies due to the same effects? JHEP 10 (2018) 094 1804.04474
55 LHCb Collaboration Multiplicity dependence of $ \sigma_{\psi $ (2S) $ }/\sigma_{\text{J}/\psi} $ in pp collisions at $ \sqrt{s}= $ 13 TeV JHEP 05 (2024) 243 2312.15201
56 ALICE Collaboration Measurement of $ \psi $ (2S) production as a function of charged-particle pseudorapidity density in pp collisions at $ \sqrt{s} = $ 13 TeV and p--Pb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 8.16 TeV with ALICE at the LHC JHEP 06 (2023) 147 2204.10253
57 LHCb Collaboration Prompt and nonprompt $ \psi $ (2S) production in $ \mathrm{p} $Pb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 8.16 TeV JHEP 04 (2024) 111 2401.11342
58 Particle Data Group Collaboration Review of particle physics PRD 110 (2024) 030001
59 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004
60 CMS Collaboration Development of the CMS detector for the CERN LHC Run 3 JINST 19 (2024) P05064 CMS-PRF-21-001
2309.05466
61 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
62 CMS Collaboration The CMS trigger system JINST 12 (2017) P01020 CMS-TRG-12-001
1609.02366
63 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
64 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
65 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
66 CMS Collaboration Particle-flow reconstruction and global event description with the CMS detector JINST 12 (2017) P10003 CMS-PRF-14-001
1706.04965
67 CMS Collaboration Performance of CMS muon reconstruction from proton-proton to heavy ion collisions JINST 19 (2024) P09012 CMS-MUO-21-001
2404.17377
68 CMS Collaboration Charged-particle nuclear modification factors in PbPb and $ \mathrm{p} $Pb collisions at $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}= $ 5.02 TeV JHEP 04 (2017) 039 CMS-HIN-15-015
1611.01664
69 CMS Collaboration Constraints on the chiral magnetic effect using charge-dependent azimuthal correlations in $ \mathrm{p} $Pb and PbPb collisions at the CERN Large Hadron Collider Phys. Rev. C 97 (2018) 044912 CMS-HIN-17-001
1708.01602
70 CMS Collaboration Observation of correlated azimuthal anisotropy fourier harmonics in pp and $ \mathrm{p} $Pb collisions at the LHC PRL 120 (2018) 092301 CMS-HIN-16-022
1709.09189
71 CMS Collaboration Multiplicity and transverse momentum dependence of two-and four-particle correlations in $ \mathrm{p} $Pb and PbPb collisions PLB 724 (2013) 213 CMS-HIN-13-002
1305.0609
72 C. Bierlich et al. A comprehensive guide to the physics and usage of PYTHIA 8.3 SciPost Phys. Codeb. 2022 (2022) 8 2203.11601
73 CMS Collaboration Event generator tunes obtained from underlying event and multiparton scattering measurements EPJC 76 (2016) 155 CMS-GEN-14-001
1512.00815
74 D. J. Lange The EvtGen particle decay simulation package NIM A 462 (2001) 152
75 N. Davidson, T. Przedzinski, and Z. Was PHOTOS interface in C++: Technical and physics documentation Comput. Phys. Commun. 199 (2016) 86 1011.0937
76 T. Pierog et al. EPOS LHC: Test of collective hadronization with data measured at the CERN Large Hadron Collider Phys. Rev. C 92 (2015) 034906 1306.0121
77 GEANT4 Collaboration GEANT 4---a simulation toolkit NIM A 506 (2003) 250
78 CMS Collaboration Measurement of the inclusive W and Z production cross sections in pp collisions at $ \sqrt{s}= $ 7 TeV JHEP 10 (2011) 132 CMS-EWK-10-005
1107.4789
79 CMS Collaboration HEPData record for this analysis link
80 M. J. Oreglia A study of the reactions $ \psi^{\prime} \to \gamma \gamma \psi $ PhD thesis, Stanford University, SLAC Report SLAC-R-236, 1980
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