CMS-PAS-EXO-21-019

CMS-PAS-EXO-21-019
A search for pair production of leptoquarks decaying to muons and bottom quarks at $\sqrt{s}=$ 13 TeV
CMS Collaboration
21 August 2023

Abstract: A search for pair production of leptoquarks each decaying to a muon and a b quark is performed using proton-proton collision data collected at $\sqrt{s}=$ 13 TeV in 2016-2018 with the CMS detector at the CERN LHC, corresponding to an integrated luminosity of 138 fb $^{-1}$ . Scalar leptoquarks with masses less than 1810 GeV are excluded, assuming a 100% branching fraction of the leptoquark to a muon and a b quark. These limits represent the most stringent limits to date on leptoquarks decaying to muons and b quarks.
Links: CDS record (PDF) ; Physics Briefing ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PRD. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Dominant leading-order Feynman diagrams for pair production of LQs at the LHC.
png pdf	Figure 1-a: Dominant leading-order Feynman diagrams for pair production of LQs at the LHC.
png pdf	Figure 1-b: Dominant leading-order Feynman diagrams for pair production of LQs at the LHC.
png pdf	Figure 1-c: Dominant leading-order Feynman diagrams for pair production of LQs at the LHC.
png pdf	Figure 1-d: Dominant leading-order Feynman diagrams for pair production of LQs at the LHC.
png pdf	Figure 2: Comparison of data and background $m_{\mu\mu}$ distribution at the preselection level for the $\mathrm{Z}/\gamma^*\mathrm{+jets}$ + $\mathrm{t} \overline{\mathrm{t}}$ +jets (left) and diboson + ${\mathrm{t}\overline{\mathrm{t}}} \mathrm{V}$ (right) background control regions. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 2-a: Comparison of data and background $m_{\mu\mu}$ distribution at the preselection level for the $\mathrm{Z}/\gamma^*\mathrm{+jets}$ + $\mathrm{t} \overline{\mathrm{t}}$ +jets (left) and diboson + ${\mathrm{t}\overline{\mathrm{t}}} \mathrm{V}$ (right) background control regions. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 2-b: Comparison of data and background $m_{\mu\mu}$ distribution at the preselection level for the $\mathrm{Z}/\gamma^*\mathrm{+jets}$ + $\mathrm{t} \overline{\mathrm{t}}$ +jets (left) and diboson + ${\mathrm{t}\overline{\mathrm{t}}} \mathrm{V}$ (right) background control regions. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 3: Comparison of data and background $p_{\mathrm{T}}$ distribution at the preselection level for the leading two muons and jets. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 3-a: Comparison of data and background $p_{\mathrm{T}}$ distribution at the preselection level for the leading two muons and jets. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 3-b: Comparison of data and background $p_{\mathrm{T}}$ distribution at the preselection level for the leading two muons and jets. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 3-c: Comparison of data and background $p_{\mathrm{T}}$ distribution at the preselection level for the leading two muons and jets. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 3-d: Comparison of data and background $p_{\mathrm{T}}$ distribution at the preselection level for the leading two muons and jets. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 4: Comparison of data and background BDT discriminant distributions at preselection for LQ mass hypotheses of 1500 GeV (left), 1800 GeV (middle), and 2000 GeV (right).The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 4-a: Comparison of data and background BDT discriminant distributions at preselection for LQ mass hypotheses of 1500 GeV (left), 1800 GeV (middle), and 2000 GeV (right).The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 4-b: Comparison of data and background BDT discriminant distributions at preselection for LQ mass hypotheses of 1500 GeV (left), 1800 GeV (middle), and 2000 GeV (right).The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 4-c: Comparison of data and background BDT discriminant distributions at preselection for LQ mass hypotheses of 1500 GeV (left), 1800 GeV (middle), and 2000 GeV (right).The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 5: Data and background event yields after final selections, for each scalar $m_{\mathrm{LQ}}$ hypothesis. Each bin on the $x$ axis represents an independent $m_{\mathrm{LQ}}$ category, for example the first bin is a comparison of the yields after final selection in the $m_{\mathrm{LQ}} =$ 300 GeV signal mass hypothesis, and so on. The shaded band represents the combined statistical and systematic uncertainty in the full background estimate.
png pdf	Figure 6: The expected and observed upper limits at 95% CL on the product of the scalar LQ pair production cross section and the branching fractions $\beta^2$ as a function of $m_{\mathrm{LQ}}$ . The solid lines represent the observed limits, the dashed lines represent the median expected limits, and the inner dark-green and outer light-yellow bands represent the 68% and 95% CL intervals. The $\sigma_{\text{theory}}$ curves and their blue bands represent the theoretical scalar LQ pair production cross sections and the uncertainties on the cross sections due to the PDF prediction and renormalization and factorization scales, respectively.

Tables
png pdf	Table 1: Systematic uncertainties in combined 2016, 2017, and 2018 signal acceptance and background yields, shown as a range over all final selections (second and third columns) as well as for the $m_{\mathrm{LQ}} =$ 1800 GeV point (rightmost two columns). The bottom two lines show the total systematic uncertainty and the total statistical uncertainty in the simulated samples, respectively.
png pdf	Table 2: Event yields in combined 2016, 2017, and 2018 data at the final selection level. Uncertainties are statistical unless otherwise indicated.
png pdf	Table 3: Total signal selection efficiency, defined as events passing final selection divided by number of generated events. Uncertainties are statistical.

Summary

A search has been presented for pair production of leptoquarks decaying to muons and bottom quarks using proton-proton collision data collected at

$\sqrt{s} =$ 13 TeV in 2016--2018 with the CMS detector at the LHC, corresponding to an integrated luminosity of 138 fb

$^{-1}$ . Limits are set at 95% confidence level on the product of the scalar leptoquark pair production cross section and

$\beta^2$ , as a function of the leptoquark mass

$m_{\mathrm{LQ}}$ , where

$\beta$ is the branching fraction of the leptoquark to decay to a muon and a bottom quark. Leptoquarks with masses less than 1810 GeV are excluded for

$\beta=$ 1.0. This represents the most stringent limits to date on these models.

References
1	J. C. Pati and A. Salam	Unified lepton-hadron symmetry and a gauge theory of the basic interactions	PRD 8 (1973) 1240
2	J. C. Pati and A. Salam	Lepton number as the fourth color	PRD 10 (1974) 275
3	H. Georgi and S. Glashow	Unity of all elementary-particle forces	PRL 32 (1974) 438
4	H. Murayama and T. Yanagida	A viable SU(5) GUT with light leptoquark bosons	Mod. Phys. Lett. A 07 (1992) 147
5	H. Fritzsch and P. Minkowski	United interactions of leptons and hadrons	Annals Phys. 93 (1975) 193
6	G. Senjanovi \'c and A. Sokorac	Light lepto-quarks in SO(10)	Z. Phys. C 20 (1983) 255
7	P. H. Frampton and B.-H. Lee	SU(15) grand unification	PRL 64 (1990) 619
8	P. H. Frampton and T. W. Kephart	Higgs sector and proton decay in SU(15q) grand unification	PRD 42 (1990) 3892
9	B. Schrempp and F. Schrempp	Light leptoquarks	PLB 153 (1985) 101
10	S. Dimopoulos and L. Susskind	Mass without scalars	NPB 155 (1979) 237
11	S. Dimopoulos	Technicolored signatures	NPB 168 (1980) 69
12	E. Eichten and K. Lane	Dynamical breaking of the weak interaction symmetries	PLB 90 (1980) 85
13	J. L. Hewett and T. G. Rizzo	Low-energy phenomenology of superstring-inspired E $_{6}$ models	PL 183 (1989) 193
14	G. R. Farrar and P. Fayet	Phenomenology of the production, decay, and detection of new hadronic states associated with supersymmetry	PLB 76 (1978) 575
15	P. Ramond	Dual theory for free fermions	PRD 3 (1971) 2415
16	Y. A. Golfand and E. P. Likhtman	Extension of the algebra of Poincaré group generators and violation of p invariance	JETP Lett. 13 (1971) 323
17	A. Neveu and J. H. Schwarz	Factorizable dual model of pions	NPB 31 (1971) 86
18	D. V. Volkov and V. P. Akulov	Possible universal neutrino interaction	JETP Lett. 16 (1972) 438
19	J. Wess and B. Zumino	A Lagrangian model invariant under supergauge transformations	PLB 49 (1974) 52
20	J. Wess and B. Zumino	Supergauge transformations in four dimensions	NPB 70 (1974) 39
21	P. Fayet	Supergauge invariant extension of the Higgs mechanism and a model for the electron and its neutrino	NPB 90 (1975) 104
22	H. P. Nilles	Supersymmetry, supergravity and particle physics	Phys. Rept. 110 (1984) 1
23	R. Barbier et al.	R-parity violating supersymmetry	Phys. Rept. 420 (2005) 1	hep-ph/0406039
24	BaBar Collaboration	Evidence for an excess of $\bar{B} \to D^{(*)} \tau^-\bar{\nu}_\tau$ decays	PRL 109 (2012) 101802	1205.5442
25	BaBar Collaboration	Measurement of an Excess of $\bar{B} \to D^{(*)}\tau^- \bar{\nu}_\tau$ Decays and Implications for Charged Higgs Bosons	PRD 88 (2013) 07	1303.0571
26	Belle Collaboration	Measurement of the branching ratio of $\bar{B} \to D^{(\ast)} \tau^- \bar{\nu}_\tau$ relative to $\bar{B} \to D^{(\ast)} \ell^- \bar{\nu}_\ell$ decays with hadronic tagging at Belle	PRD 92 (2015) 07	1507.03233
27	Belle Collaboration	Measurement of the $\tau$ lepton polarization and $R(D^)$ in the decay $\bar{B} \to D^ \tau^- \bar{\nu}_\tau$	PRL 118 (2017) 211801	1612.00529
28	Belle Collaboration	Measurement of the $\tau$ lepton polarization and $R(D^)$ in the decay $\bar{B} \rightarrow D^ \tau^- \bar{\nu}_\tau$ with one-prong hadronic $\tau$ decays at Belle	PRD 97 (2018) 01	1709.00129
29	Belle Collaboration	Measurement of $\mathcal{R}(D)$ and $\mathcal{R}(D^*)$ with a semileptonic tagging method	PRL 124 (2020) 161803	1910.05864
30	LHCb Collaboration	Measurement of the ratio of branching fractions $\mathcal{B}(\bar{B}^0 \to D^{+}\tau^{-}\bar{\nu}_{\tau})/\mathcal{B}(\bar{B}^0 \to D^{+}\mu^{-}\bar{\nu}_{\mu})$	PRL 115 (2015) 111803	1506.08614
31	LHCb Collaboration	Measurement of the ratio of the $B^0 \to D^{-} \tau^+ \nu_{\tau}$ and $B^0 \to D^{-} \mu^+ \nu_{\mu}$ branching fractions using three-prong $\tau$ -lepton decays	PRL 120 (2018) 171802	1708.08856
32	LHCb Collaboration	Test of Lepton Flavor Universality by the measurement of the $B^0 \to D^{*-} \tau^+ \nu_{\tau}$ branching fraction using three-prong $\tau$ decays	PRD 97 (2018) 07	1711.02505
33	LHCb Collaboration	Search for lepton-universality violation in ${B}^{+}\rightarrow{K}^{+}{\ell}^{+}{\ell}^{-}$ decays	PRL 12 (2019) 191801
34	LHCb Collaboration	Test of lepton universality with $B^{0} \rightarrow K^{*0}\ell^{+}\ell^{-}$ decays	JHEP 08 (2017) 055	1705.05802
35	LHCb Collaboration	Measurement of the ratio of branching fractions $\mathcal{B}(B_c^+\,\to\,J/\psi\tau^+\nu_\tau)$ / $\mathcal{B}(B_c^+\,\to\,J/\psi\mu^+\nu_\mu)$	PRL 120 (2018) 121801	1711.05623
36	CMS, LHCb Collaboration	Observation of the rare $B^0_s\to\mu^+\mu^-$ decay from the combined analysis of CMS and LHCb data	Nature 522 (2015) 68	1411.4413
37	LHCb Collaboration	Measurement of lepton universality parameters in $B^+\to K^+\ell^+\ell^-$ and $B^0\to K^{*0}\ell^+\ell^-$ decays	PRD 108 (2023) 03	2212.09153
38	LHCb Collaboration	Test of lepton flavor universality using $B^0 \to D^{*-}\tau^+\nu_{\tau}$ decays with hadronic $\tau$ channels	PRD 108 (2023) 01	2305.01463
39	LHCb Collaboration	Measurement of the ratios of branching fractions $\mathcal{R}(D^{*})$ and $\mathcal{R}(D^{0})$		2302.02886
40	Muon $g\ensuremath - 2$ Collaboration	Final report of the E821 muon anomalous magnetic moment measurement at BNL	PRD 73 (2006) 072003
41	Muon $g\ensuremath - 2$ Collaboration	Measurement of the positive muon anomalous magnetic moment to 0.46 ppm	PRL 126 (2021) 141801
42	B. Diaz, M. Schmaltz, and Y.-M. Zhong	The leptoquark Hunter's guide: Pair production	JHEP 10 (2017) 097	1706.05033
43	W. Buchm \"u ller, R. R \"u ckl, and D. Wyler	Leptoquarks in lepton-quark collisions	PLB 191 (1987) 442
44	J. Blumlein, E. Boos, and A. Kryukov	Leptoquark pair production in hadronic interactions	Z. Phys. C 76 (1997) 137	hep-ph/9610408
45	CMS Collaboration	Search for pair production of second-generation leptoquarks at $\sqrt{s}=13\text{ }\text{ }\mathrm{TeV}$	PRD 9 (2019) 032014
46	ATLAS Collaboration	Search for pairs of scalar leptoquarks decaying into quarks and electrons or muons in $\sqrt{s}$ = 13 TeV $pp$ collisions with the ATLAS detector	JHEP 10 (2020) 112	2006.05872
47	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004
48	CMS Collaboration	Technical proposal for the Phase-II upgrade of the Compact Muon Solenoid	CMS Technical Proposal CERN-LHCC-2015-010, CMS-TDR-15-02, 2015 CDS
49	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
50	M. Cacciari, G. P. Salam, and G. Soyez	The anti- $k_t$ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
51	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
52	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
53	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
54	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
55	E. Bols et al.	Jet flavour classification using DeepJet	JINST 15 (2020) P12012	2008.10519
56	CMS Collaboration	Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV	JINST 13 (2018) P05011	CMS-BTV-16-002 1712.07158
57	CMS Collaboration	Performance of the DeepJet b tagging algorithm using 41.9/fb of data from proton-proton collisions at 13 TeV with Phase 1 CMS detector	CMS Detector Performance Note CMS-DP-2018-058, 2018 CDS
58	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
59	CMS Collaboration	The CMS trigger system	JINST 12 (2017) P01020	CMS-TRG-12-001 1609.02366
60	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
61	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $\sqrt{s}=$ 13 TeV	CMS Physics Analysis Summary, 2018 CMS-PAS-LUM-17-004	CMS-PAS-LUM-17-004
62	CMS Collaboration	CMS luminosity measurement for the 2018 data-taking period at $\sqrt{s}=$ 13 TeV	CMS Physics Analysis Summary, 2019 CMS-PAS-LUM-18-002	CMS-PAS-LUM-18-002
63	CMS Collaboration	CMS luminosity measurement for the 2017 data-taking period at $\sqrt{s}$ = 13 TeV	CMS Physics Analysis Summary, 2018 link	CMS-PAS-LUM-17-004
64	CMS Collaboration	CMS luminosity measurement for the 2018 data-taking period at $\sqrt{s}$ = 13 TeV	CMS Physics Analysis Summary, 2019 link	CMS-PAS-LUM-18-002
65	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
66	S. Frixione and B. R. Webber	Matching NLO QCD computations and parton shower simulations	JHEP 06 (2002) 029	hep-ph/0204244
67	I. Dor \v s ner et al.	Physics of leptoquarks in precision experiments and at particle colliders	Phys. Rept. 641 (2016) 1	1603.04993
68	I. Doršner and A. Greljo	Leptoquark toolbox for precision collider studies	JHEP 201 (2018) 126
69	M. Kr ä mer, T. Plehn, M. Spira, and P. M. Zerwas	Pair production of scalar leptoquarks at the CERN LHC	PRD 71 (2005) 057503
70	T. Mandal, S. Mitra, and S. Seth	Pair production of scalar leptoquarks at the lhc to nlo parton shower accuracy	PRD 93 (2016) 035018
71	J. Butterworth et al.	PDF4LHC recommendations for LHC Run II	JPG 43 (2016) 023001	1510.03865
72	S. Frixione, P. Nason, and C. Oleari	Matching NLO QCD computations with parton shower simulations: the POWHEG method	JHEP 11 (2007) 070	0709.2092
73	S. Alioli, P. Nason, C. Oleari, and E. Re	A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX	JHEP 06 (2010) 043	1002.2581
74	S. Alioli, P. Nason, C. Oleari, and E. Re	NLO vector-boson production matched with shower in POWHEG	JHEP 07 (2008) 060	0805.4802
75	S. Alioli, P. Nason, C. Oleari, and E. Re	NLO single-top production matched with shower in POWHEG: $s$ - and $t$ -channel contributions	JHEP 09 (2009) 111	0907.4076
76	S. Frixione, E. Laenen, P. Motylinski, and B. R. Webber	Single-top production in MC@NLO	JHEP 03 (2006) 092	hep-ph/0512250
77	T. Sjöstrand et al.	An Introduction to PYTHIA 8.2	Comput. Phys. Commun. 191 (2015) 159	1410.3012
78	NNPDF Collaboration	Parton distributions for the LHC Run II	JHEP 04 (2015) 040	1410.8849
79	GEANT4 Collaboration	GEANT 4---A simulation toolkit	NIM A 506 (2003) 250
80	J. Allison et al.	GEANT 4 developments and applications	IEEE Trans. Nucl. Sci. 53 (2006) 270
81	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
82	CMS Collaboration	Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements	EPJC 80 (2020) 1	CMS-GEN-17-001 1903.12179
83	G. Punzi	Sensitivity of searches for new signals and its optimization	in Statistical problems in particle physics, astrophysics and cosmology, Stanford, 2003 PHYSTAT 200 (2003) 3	physics/0308063
84	CMS Collaboration	Search for high-mass resonances in dilepton final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV		CMS-EXO-16-047 1803.06292
85	M. Botje et al.	The PDF4LHC Working Group Interim Recommendations		1101.0538
86	D. Bourilkov, R. C. Group, and M. R. Whalley	LHAPDF: PDF use from the Tevatron to the LHC		hep-ph/0605240
87	CMS Collaboration	Measurement of the inelastic proton-proton cross section at $\sqrt{s}=$ 13 TeV	JHEP 07 (2018) 161	CMS-FSQ-15-005 1802.02613
88	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
89	T. Junk	Confidence level computation for combining searches with small statistics	NIM A 434 (1999) 435	hep-ex/9902006
90	A. L. Read	Presentation of search results: The CL $_{\rm{s}}$ technique	JPG 28 (2002) 2693