CMS-HIN-22-001

CMS-HIN-22-001 ; CERN-EP-2024-138
Search for nuclear modifications of ${\mathrm{B}^{+}}$ meson production in pPb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 8.16 TeV
CMS Collaboration
7 July 2024
Phys. Rev. Lett. 134 (2025) 111903
Abstract: Nuclear medium effects on ${\mathrm{B}^{+}}$ meson production are studied using the binary-collision scaled cross section ratio between events of different multiplicities from proton-lead collisions. Data, collected by the CMS experiment in 2016 at a nucleon-nucleon center-of-mass energy of $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 8.16 TeV, corresponding to an integrated luminosity of 175 nb $^{-1}$ , were used. The scaling factors in the ratio are determined using a novel approach based on the $\mathrm{Z}\to\mu^{-}\mu^{+}$ cross sections measured in the same events. The scaled ratio for ${\mathrm{B}^{+}}$ is consistent with unity for all event multiplicities, putting stringent constraints on nuclear modification for heavy flavor.
Links: e-print arXiv:2407.05402 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Reconstructed $\psi(\text{2S}) \mathrm{K^+}$ invariant mass distributions for ${\mathrm{B}^{+}}$ meson candidates with 3 $< p_{\mathrm{T}} <$ 50 GeV, in events with 2 $< N_{\text{ch}} <$ 60 (left) or 110 $< N_{\text{ch}} <$ 250 (right). The result of the fit described in the text is also shown.
png pdf	Figure 1-a: Reconstructed $\psi(\text{2S}) \mathrm{K^+}$ invariant mass distributions for ${\mathrm{B}^{+}}$ meson candidates with 3 $< p_{\mathrm{T}} <$ 50 GeV, in events with 2 $< N_{\text{ch}} <$ 60 (left) or 110 $< N_{\text{ch}} <$ 250 (right). The result of the fit described in the text is also shown.
png pdf	Figure 1-b: Reconstructed $\psi(\text{2S}) \mathrm{K^+}$ invariant mass distributions for ${\mathrm{B}^{+}}$ meson candidates with 3 $< p_{\mathrm{T}} <$ 50 GeV, in events with 2 $< N_{\text{ch}} <$ 60 (left) or 110 $< N_{\text{ch}} <$ 250 (right). The result of the fit described in the text is also shown.
png pdf	Figure 2: (left) ${\mathrm{B}^{+}}$ differential cross section in $p_{\mathrm{T}}$ bins. Vertical bars (boxes) represent the statistical (systematic) uncertainties. The global systematic uncertainty, not included in the data points, comprises the uncertainties in the integrated luminosity measurement and the ${\mathrm{B}^{+}}$ meson branching fraction. Results are compared to FONLL calculations, scaled by the number of binary nucleon-nucleon collisions. The yellow boxes represent the theoretical uncertainties from FONLL calculations [38,39,40]. (right) ${\mathrm{B}^{+}}$ differential cross section shown in $p_{\mathrm{T}}$ bins divided into classes of $N_{\text{ch}}$ . For better visibility, data points are scaled by a factor of 2 (blue), 4 (magenta), or 8 (red). Vertical bars represent total uncertainties.
png pdf	Figure 2-a: (left) ${\mathrm{B}^{+}}$ differential cross section in $p_{\mathrm{T}}$ bins. Vertical bars (boxes) represent the statistical (systematic) uncertainties. The global systematic uncertainty, not included in the data points, comprises the uncertainties in the integrated luminosity measurement and the ${\mathrm{B}^{+}}$ meson branching fraction. Results are compared to FONLL calculations, scaled by the number of binary nucleon-nucleon collisions. The yellow boxes represent the theoretical uncertainties from FONLL calculations [38,39,40]. (right) ${\mathrm{B}^{+}}$ differential cross section shown in $p_{\mathrm{T}}$ bins divided into classes of $N_{\text{ch}}$ . For better visibility, data points are scaled by a factor of 2 (blue), 4 (magenta), or 8 (red). Vertical bars represent total uncertainties.
png pdf	Figure 2-b: (left) ${\mathrm{B}^{+}}$ differential cross section in $p_{\mathrm{T}}$ bins. Vertical bars (boxes) represent the statistical (systematic) uncertainties. The global systematic uncertainty, not included in the data points, comprises the uncertainties in the integrated luminosity measurement and the ${\mathrm{B}^{+}}$ meson branching fraction. Results are compared to FONLL calculations, scaled by the number of binary nucleon-nucleon collisions. The yellow boxes represent the theoretical uncertainties from FONLL calculations [38,39,40]. (right) ${\mathrm{B}^{+}}$ differential cross section shown in $p_{\mathrm{T}}$ bins divided into classes of $N_{\text{ch}}$ . For better visibility, data points are scaled by a factor of 2 (blue), 4 (magenta), or 8 (red). Vertical bars represent total uncertainties.
png pdf	Figure 3: The $R_{\mathrm{HL}}$ for ${\mathrm{B}^{+}}$ in $p_{\mathrm{T}}$ bins for the highest and lowest multiplicity classes (left), and in the full $p_{\mathrm{T}}$ range and as a function of the multiplicity density (right). The error bars correspond to the statistical uncertainty, and the boxes represent the sum in quadrature of systematic uncertainties.
png pdf	Figure 3-a: The $R_{\mathrm{HL}}$ for ${\mathrm{B}^{+}}$ in $p_{\mathrm{T}}$ bins for the highest and lowest multiplicity classes (left), and in the full $p_{\mathrm{T}}$ range and as a function of the multiplicity density (right). The error bars correspond to the statistical uncertainty, and the boxes represent the sum in quadrature of systematic uncertainties.
png pdf	Figure 3-b: The $R_{\mathrm{HL}}$ for ${\mathrm{B}^{+}}$ in $p_{\mathrm{T}}$ bins for the highest and lowest multiplicity classes (left), and in the full $p_{\mathrm{T}}$ range and as a function of the multiplicity density (right). The error bars correspond to the statistical uncertainty, and the boxes represent the sum in quadrature of systematic uncertainties.
png pdf	Figure 4: Z boson differential cross section in $p_{\mathrm{T}}$ bins for the different multiplicity classes. The vertical bars represent the total uncertainties.

Tables
png pdf	Table 1: Fraction of the full event sample that contains a ${\mathrm{B}^{+}}$ meson candidate in each multiplicity class, and corrected multiplicity for charged particles with $\|y\| <$ 2.4 and $p_{\mathrm{T}} >$ 0.4 GeV. Systematic uncertainties are given for the corrected multiplicities, while statistical uncertainties are negligible.
png pdf	Table 2: Summary of differential cross sections ( $\mu$ b GeV $^{-1}$ ) as a function of $p_{\mathrm{T}}$ ( ${\mathrm{B}^{+}}$ ) in pPb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}=$ 8.16 TeV. The uncertainties in the integrated luminosity measurement and the ${\mathrm{B}^{+}}$ meson branching fraction are not included in the systematic uncertainties.

Summary

In summary, the

${\mathrm{B}^{+}}$ meson differential production cross sections have been measured as a function of the meson transverse momentum in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of 8.16 TeV. The exclusive

${\mathrm{B}^{+}}\!\to\! \mathrm{J}/\psi \mathrm{K^+}$ decay channel was used to reconstruct the

${\mathrm{B}^{+}}$ mesons. The fixed-order next-to-leading logarithmic predictions are in agreement with the inclusive measurement. The

${\mathrm{B}^{+}}$ cross section has been measured for the first time in different classes of charged-particle multiplicity in pPb collisions, revealing an expected rising trend in the

${\mathrm{B}^{+}}$ production with increasing charged-particle multiplicity. The scaled ratio of

${\mathrm{B}^{+}}$ meson cross sections in high- to low-multiplicity events were used to study nuclear medium effects on heavy flavor production. The scaling factors, characterizing the relative number of binary collisions between event classes of different multiplicities, were obtained, for the first time, in a data-driven way from ratios of the measured Z boson cross sections in the same events. The observed ratios are consistent with unity within uncertainties for all event selections studied, setting constraints on possible presence of medium effects in the

${\mathrm{B}^{+}}$ meson production. The novel approach relying on the Z boson measurements to extract the scaling factors provides future opportunities for medium effect searches, particularly in small collision systems.

References
1	E. V. Shuryak	Theory of hadronic plasma	Sov. Phys. JETP 47 (1978) 212
2	J. C. Collins and M. J. Perry	Superdense matter: neutrons or asymptotically free quarks?	PRL 34 (1975) 1353
3	PHENIX Collaboration	Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration	Nucl. Phys. A 757 (2005) 184	nucl-ex/0410003
4	STAR Collaboration	Experimental and theoretical challenges in the search for the quark gluon plasma: The STAR Collaboration's critical assessment of the evidence from RHIC collisions	Nucl. Phys. A 757 (2005) 102	nucl-ex/0501009
5	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
6	CMS Collaboration	Overview of high-density QCD studies with the CMS experiment at the LHC	Submitted to Physics Reports, 2024	CMS-HIN-23-011 2405.10785
7	CMS Collaboration	Observation of long-range near-side angular correlations in proton-lead collisions at the LHC	PLB 718 (2013) 795	CMS-HIN-12-015 1210.5482
8	ATLAS Collaboration	Observation of associated near-side and away-side long-range correlations in $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV proton-lead collisions with the ATLAS detector	PRL 110 (2013) 182302	1212.5198
9	ALICE Collaboration	Long-range angular correlations on the near and away side in pPb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV	PLB 719 (2013) 29	1212.2001
10	LHCb Collaboration	Measurements of long-range near-side angular correlations in $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5 TeV proton-lead collisions in the forward region	PLB 762 (2016) 473	1512.00439
11	ALICE Collaboration	Long-range angular correlations of $\pi$ , $\mathrm{K}$ and p in p--Pb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}=$ 5.02 TeV	PLB 726 (2013) 164	1307.3237
12	CMS Collaboration	Long-range two-particle correlations of strange hadrons with charged particles in pPb and PbPb collisions at LHC energies	PLB 742 (2015) 200	CMS-HIN-14-002 1409.3392
13	CMS Collaboration	Evidence for collective multi-particle correlations in pPb collisions	PRL 115 (2015) 012301	CMS-HIN-14-006 1502.05382
14	ALICE Collaboration	Multiplicity dependence of pion, kaon, proton and lambda production in p-Pb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV	PLB 728 (2014) 25	1307.6796
15	ATLAS Collaboration	Correlated long-range mixed-harmonic fluctuations measured in pp, p+Pb and low-multiplicity PbPb collisions with the ATLAS detector	PLB 789 (2019) 444	1807.02012
16	CMS Collaboration	Observation of prompt $\mathrm{J}/\psi$ meson elliptic flow in high-multiplicity $\mathrm{p}$ Pb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}=$ 8.16 TeV	PLB 791 (2019) 172	CMS-HIN-18-010 1810.01473
17	CMS Collaboration	Measurement of prompt and nonprompt $\mathrm{J}/\psi$ production in pp and $\mathrm{p}\mathrm{Pb}$ collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}=$ 5.02 TeV	EPJC 77 (2017) 269	CMS-HIN-14-009 1702.01462
18	PHENIX Collaboration	Creation of quark-gluon plasma droplets with three distinct geometries	no.~3, 214, 2019 Nature Phys. 15 (2019)	1805.02973
19	CMS Collaboration	Elliptic anisotropy measurement of the f $_0$ (980) hadron in proton-lead collisions and evidence for its quark-antiquark composition	Submitted to Nature Physics, 2023	CMS-HIN-20-002 2312.17092
20	CMS Collaboration	Observation of long-range near-side angular correlations in proton-proton collisions at the LHC	JHEP 09 (2010) 091	CMS-QCD-10-002 1009.4122
21	ATLAS Collaboration	Observation of long-range elliptic azimuthal anisotropies in $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 13 and 2.76 TeV pp collisions with the ATLAS detector	PRL 116 (2016) 172301	1509.04776
22	CMS Collaboration	Measurement of long-range near-side two-particle angular correlations in pp collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 13 TeV	PRL 116 (2016) 172302	CMS-FSQ-15-002 1510.03068
23	CMS Collaboration	Evidence for collectivity in pp collisions at the LHC	PLB 765 (2017) 193	CMS-HIN-16-010 1606.06198
24	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
25	ALICE Collaboration	Multiplicity dependence of light-flavor hadron production in pp collisions at $\sqrt{s} =$ 7 TeV	Phys. Rev. C 99 (2019) 024906	1807.11321
26	ALICE Collaboration	Azimuthal correlations of prompt $\mathrm{D}$ mesons with charged particles in pp and p-Pb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV	EPJC 80 (2020) 979	1910.14403
27	CMS Collaboration	Observation of enhanced long-range elliptic anisotropies inside high-multiplicity jets in pp collisions at $\sqrt{s} =$ 13 TeV	Submitted to Phys. Rev. Lett, 2023	CMS-HIN-21-013 2312.17103
28	K. Dusling, W. Li, and B. Schenke	Novel collective phenomena in high-energy proton-proton and proton-nucleus collisions	Int. J. Mod. Phys. E 25 (2016) 1630002	1509.07939
29	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
30	CMS Collaboration	Studies of charm and beauty hadron long-range correlations in pp and pPb collisions at LHC energies	PLB 813 (2021) 136036	CMS-HIN-19-009 2009.07065
31	X. Dong, Y.-J. Lee, and R. Rapp	Open heavy-flavor production in heavy-ion collisions	Ann. Rev. Nucl. Part. Sci. 69 (2019) 417	1903.07709
32	L. Apolin \'a rio, Y.-J. Lee, and M. Winn	Heavy quarks and jets as probes of the QGP	Prog. Part. Nucl. Phys. 127 (2022) 103990	2203.16352
33	CMS Collaboration	Study of azimuthal anisotropy of $\Upsilon(1S)$ mesons in pPb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 8.16 TeV	PLB 850 (2024) 138518	CMS-HIN-21-001 2310.03233
34	LHCb Collaboration	Measurement of ${\mathrm{B}^{+}}$ , $\mathrm{B}_{d}$ and $\Lambda_{b}$ production in $\mathrm{p}\mathrm{Pb}$ collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}}=$ 8.16 TeV	PRD 99 (2019) 052011	1902.05599
35	STAR Collaboration	Particle type dependence of azimuthal anisotropy and nuclear modification of particle production in Au + Au collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 200 GeV	PRL 92 (2004) 052302	nucl-ex/0306007
36	PHOBOS Collaboration	Centrality dependence of charged hadron transverse momentum spectra in Au + Au collisions from $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 62.4 GeV to 200 GeV	PRL 94 (2005) 082304	nucl-ex/0405003
37	STAR Collaboration	STAR heavy-ion highlights	EPJ Web Conf. 126 (2016) 02027
38	M. Cacciari et al.	Theoretical predictions for charm and bottom production at the LHC	JHEP 10 (2012) 137	1205.6344
39	M. Cacciari, S. Frixione, and P. Nason	The $p_{\mathrm{T}}$ spectrum in heavy-flavour photoproduction	JHEP 03 (2001) 006	hep-ph/0102134
40	M. Cacciari, M. Greco, and P. Nason	The $p_{\mathrm{T}}$ spectrum in heavy-flavour hadroproduction	JHEP 05 (1998) 007	hep-ph/9803400
41	CMS Collaboration	HEPData record for this analysis	link
42	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004
43	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
44	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
45	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
46	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
47	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
48	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
49	CMS Collaboration	Performance of reconstruction and identification of $\tau$ leptons decaying to hadrons and $\nu_{\!\tau}$ in pp collisions at $\sqrt{s}=$ 13 TeV	JINST 13 (2018) P10005	CMS-TAU-16-003 1809.02816
50	CMS Collaboration	Jet energy scale and resolution in the CMS experiment in pp collisions at 8 TeV	JINST 12 (2017) P02014	CMS-JME-13-004 1607.03663
51	CMS Collaboration	Performance of missing transverse momentum reconstruction in proton-proton collisions at $\sqrt{s} =$ 13 TeV using the CMS detector	JINST 14 (2019) P07004	CMS-JME-17-001 1903.06078
52	CMS Collaboration	Charged-particle nuclear modification factors in PbPb and $\mathrm{p}\mathrm{Pb}$ collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV	JHEP 04 (2017) 039	CMS-HIN-15-015 1611.01664
53	Particle Data Group Collaboration	Review of particle physics	PTEP 2022 (2022) 083C01
54	T. Sjöstrand et al.	An introduction to PYTHIA 8.2	Comput. Phys. Commun. 191 (2015) 159	1410.3012
55	D. Lange	The EVTGEN particle decay simulation package	NIM A 462 (2001) 152
56	N. Davidson, T. Przedzinski, and Z. Was	PHOTOS interface in C++: technical and physics documentation	Comput. Phys. Commun. 199 (2016) 86	1011.0937
57	GEANT4 Collaboration	GEANT 4---a simulation toolkit	NIM A 506 (2003) 250
58	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
59	CMS Collaboration	Tracking POG results for pion efficiency with the $\mathrm{D}^{*}$ meson using data from 2016 and 2017	CMS Detector Performance Report CMS-DP-2018-050, 2018 CDS
60	CMS Collaboration	Supplemental material: ${\mathrm{B}^{+}}$ meson and Z boson differential cross sections	\href link
61	CMS Collaboration	Prompt and nonprompt $\mathrm{J}/\psi$ production in pp collisions at $\sqrt{s}=$ 7 TeV	EPJC 71 (2011) 1575	CMS-BPH-10-002 1011.4193
62	N. L. Johnson	Systems of frequency curves generated by methods of translation	Biometrika 36 (1949) 149
63	S. Jackman	Bayesian analysis for the social sciences	John Wiley \& Sons, New Jersey, USA, 2009 link
64	CMS Collaboration	CMS luminosity measurement using 2016 proton-nucleus collisions at nucleon-nucleon center-of-mass energy of 8.16 TeV	CMS Physics Analysis Summary, 2018 CMS-PAS-LUM-17-002	CMS-PAS-LUM-17-002
65	M. L. Miller, K. Reygers, S. J. Sanders, and P. Steinberg	Glauber modeling in high energy nuclear collisions	Ann. Rev. Nucl. Part. Sci. 57 (2007) 205	nucl-ex/0701025
66	CMS Collaboration	Study of Drell-Yan dimuon production in proton-lead collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 8.16 TeV	JHEP 05 (2021) 182	CMS-HIN-18-003 2102.13648