CMS-SUS-18-001

CMS-SUS-18-001 ; CERN-EP-2018-109
Constraints on models of scalar and vector leptoquarks decaying to a quark and a neutrino at $\sqrt{s} = $ 13 TeV
CMS Collaboration
25 May 2018
Phys. Rev. D 98 (2018) 032005
Abstract: The results of a previous search by the CMS Collaboration for squarks and gluinos are reinterpreted to constrain models of leptoquark (LQ) production. The search considers jets in association with a transverse momentum imbalance, using the $ {M_{\mathrm{T2}}} $ variable. The analysis uses proton-proton collision data at $\sqrt{s} = $ 13 TeV, recorded with the CMS detector at the LHC in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Leptoquark pair production is considered with LQ decays to a neutrino and a top, bottom, or light quark. This reinterpretation considers higher mass values than the original CMS search to constrain both scalar and vector LQs. Limits on the cross section for LQ pair production are derived at the 95% confidence level depending on the LQ decay mode. A vector LQ decaying with a 50% branching fraction to $ {\mathrm{t}\nu} $, and 50% to $ {\mathrm{b}\tau} $, has been proposed as part of an explanation of anomalous flavor physics results. In such a model, using only the decays to $ {\mathrm{t}\nu} $, LQ masses below 1530 GeV are excluded assuming the Yang-Mills case with coupling $\kappa = $ 1, placing the most stringent constraint to date from pair production of vector LQs.
Links: e-print arXiv:1805.10228 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	References	CMS Publications

Additional information on efficiencies needed for reinterpretation of these results are available here.
Additional technical material for CMS speakers can be found here.

Figures
png pdf	Figure 1: Dominant LO diagrams for LQ pair production in proton-proton collisions.
png pdf	Figure 1-a: One of the dominant LO diagram for LQ pair production in proton-proton collisions.
png pdf	Figure 1-b: One of the dominant LO diagram for LQ pair production in proton-proton collisions.
png pdf	Figure 1-c: One of the dominant LO diagram for LQ pair production in proton-proton collisions.
png pdf	Figure 1-d: One of the dominant LO diagram for LQ pair production in proton-proton collisions.
png pdf	Figure 2: Distributions of $ {M_{\mathrm {T2}}} $ showing data, the background predictions, and a hypothetical $ {\mathrm {LQ}_{\mathrm {V}}} $ signal with LQ mass of 1500 GeV decaying with 100% branching fraction to $ {{\mathrm {t}} {\nu}} _{\tau}$. The cross section used for the $ {\mathrm {LQ}_{\mathrm {V}}} $ signal assumes $\kappa = $ 1, and the signal is stacked on top of the background predictions. The black points show the observed data, with the statistical uncertainties represented by the vertical bars, and the bin widths represented by the horizontal bars. The rightmost bin in each plot also includes events with larger values of $ {M_{\mathrm {T2}}} $. The hatched band shows the uncertainty in the background prediction including both statistical and systematic components. The lower pane of each plot shows the ratio of observed data over predicted background. The categories require $ {H_{\mathrm {T}}} > $ 1500 GeV, 4 $ \leq {N_{\mathrm {j}}} \leq $ 6, and (left) $ {N_{{\mathrm {b}}}} = $ 1 or (right) $ {N_{{\mathrm {b}}}} = $ 2.
png pdf	Figure 2-a: Distribution of $ {M_{\mathrm {T2}}} $ showing data, the background predictions, and a hypothetical $ {\mathrm {LQ}_{\mathrm {V}}} $ signal with LQ mass of 1500 GeV decaying with 100% branching fraction to $ {{\mathrm {t}} {\nu}} _{\tau}$. The cross section used for the $ {\mathrm {LQ}_{\mathrm {V}}} $ signal assumes $\kappa = $ 1, and the signal is stacked on top of the background predictions. The black points show the observed data, with the statistical uncertainties represented by the vertical bars, and the bin widths represented by the horizontal bars. The rightmost bin in the plot also includes events with larger values of $ {M_{\mathrm {T2}}} $. The hatched band shows the uncertainty in the background prediction including both statistical and systematic components. The lower pane shows the ratio of observed data over predicted background. The categories require $ {H_{\mathrm {T}}} > $ 1500 GeV, 4 $ \leq {N_{\mathrm {j}}} \leq $ 6, and $ {N_{{\mathrm {b}}}} = $ 1.
png pdf	Figure 2-b: Distribution of $ {M_{\mathrm {T2}}} $ showing data, the background predictions, and a hypothetical $ {\mathrm {LQ}_{\mathrm {V}}} $ signal with LQ mass of 1500 GeV decaying with 100% branching fraction to $ {{\mathrm {t}} {\nu}} _{\tau}$. The cross section used for the $ {\mathrm {LQ}_{\mathrm {V}}} $ signal assumes $\kappa = $ 1, and the signal is stacked on top of the background predictions. The black points show the observed data, with the statistical uncertainties represented by the vertical bars, and the bin widths represented by the horizontal bars. The rightmost bin in the plot also includes events with larger values of $ {M_{\mathrm {T2}}} $. The hatched band shows the uncertainty in the background prediction including both statistical and systematic components. The lower pane shows the ratio of observed data over predicted background. The categories require $ {H_{\mathrm {T}}} > $ 1500 GeV, 4 $ \leq {N_{\mathrm {j}}} \leq $ 6, and $ {N_{{\mathrm {b}}}} = $ 2.
png pdf	Figure 3: The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with 100% branching fraction to a neutrino and (upper left) a light quark (one of u, d, s, or c), (upper right) a bottom quark, or (lower) a top quark. The solid (dashed) black line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95%) of the distribution of limits expected under the background-only hypothesis. The blue (red) lines show the theoretical cross section for $ {\mathrm {LQ}_{\mathrm {S}}} ( {\mathrm {LQ}_{\mathrm {V}}} ) $ pair production with its uncertainty. (lower) Also shown in magenta is the product of the theoretical cross section and the square of the branching fraction ($B$), for vector LQ pair production assuming a 50% branching fraction to $ {{\mathrm {t}} {\nu}} _{\tau}$, with the remaining 50% to ${{\mathrm {b}} {\tau}}$.
png pdf root	Figure 3-a: The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with 100% branching fraction to a neutrino and a light quark (one of u, d, s, or c). The solid (dashed) black line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95%) of the distribution of limits expected under the background-only hypothesis. The blue (red) lines show the theoretical cross section for $ {\mathrm {LQ}_{\mathrm {S}}} ( {\mathrm {LQ}_{\mathrm {V}}} ) $ pair production with its uncertainty.
png pdf root	Figure 3-b: The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with 100% branching fraction to a neutrino and a bottom quark. The solid (dashed) black line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95%) of the distribution of limits expected under the background-only hypothesis. The blue (red) lines show the theoretical cross section for $ {\mathrm {LQ}_{\mathrm {S}}} ( {\mathrm {LQ}_{\mathrm {V}}} ) $ pair production with its uncertainty.
png pdf root	Figure 3-c: The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with 100% branching fraction to a neutrino and a top quark. The solid (dashed) black line represents the observed (median expected) exclusion. The inner green (outer yellow) band indicates the region containing 68 (95%) of the distribution of limits expected under the background-only hypothesis. The blue (red) lines show the theoretical cross section for $ {\mathrm {LQ}_{\mathrm {S}}} ( {\mathrm {LQ}_{\mathrm {V}}} ) $ pair production with its uncertainty. Also shown in magenta is the product of the theoretical cross section and the square of the branching fraction ($B$), for vector LQ pair production assuming a 50% branching fraction to $ {{\mathrm {t}} {\nu}} _{\tau}$, with the remaining 50% to ${{\mathrm {b}} {\tau}}$.

Summary

The CMS search for jets and missing transverse momentum using the $ {M_{\mathrm{T2}}} $ variable has been reinterpreted to place limits on leptoquark (LQ) pair production, where the LQ decays with 100% branching fraction to a quark and a neutrino. The search uses proton-proton collision data at $\sqrt{s} = $ 13 TeV, recorded with the CMS detector in 2016 and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. Leptoquark decays to a neutrino and a top, bottom, or light quark are considered. Compared to the original result, higher masses are considered to place exclusion limits on both scalar and vector LQs. Assuming that there is only one LQ state within mass reach of the LHC, for a scalar (vector) LQ decaying to a light quark and a neutrino, masses below 980 (1790) GeV are excluded at the 95% confidence level by the observed data. For an LQ decaying to $ {\mathrm{b}\nu} $, masses below 1100 (1810) GeV are excluded, and for an LQ decaying to $ {\mathrm{t}\nu} $, masses below 1020 (1780) GeV are excluded. At high LQ mass values, these results improve the upper limits on LQ pair production cross sections over the extrapolation assumed in Ref. [39] by factors of as much as 1.2, 1.5, and 2.8 for the light quark and neutrino, $ {\mathrm{b}\nu} $, and $ {\mathrm{t}\nu} $ cases respectively. In the model of Refs. [37,38], a vector LQ with 50% branching fraction to $ {\mathrm{t}\nu} $, and 50% to $ {\mathrm{b}\tau} $, is predicted to explain anomalous flavor physics results. Masses below 1530 GeV are excluded for such a state assuming the Yang-Mills case with coupling $\kappa = $ 1, considering only the events with both LQ decaying to $ {\mathrm{t}\nu} $, providing the strongest constraint to date in this model from pair production.

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, . [Erratum: \DOI10.1103/PhysRevD.11.703.2]
3	H. Georgi and S. L. Glashow	Unity of all elementary particle forces	PRL 32 (1974) 438
4	H. Fritzsch and P. Minkowski	Unified interactions of leptons and hadrons	Ann. Phys. 93 (1975) 193
5	S. Dimopoulos and L. Susskind	Mass without scalars	NPB 155 (1979) 237
6	S. Dimopoulos	Technicolored signatures	NPB 168 (1980) 69
7	E. Farhi and L. Susskind	Technicolor	PR 74 (1981) 277
8	K. D. Lane and M. V. Ramana	Walking technicolor signatures at hadron colliders	PRD 44 (1991) 2678
9	B. Schrempp and F. Schrempp	Light leptoquarks	PLB 153 (1985) 101
10	B. Gripaios	Composite leptoquarks at the LHC	JHEP 02 (2010) 045	0910.1789
11	G. R. Farrar and P. Fayet	Phenomenology of the production, decay, and detection of new hadronic states associated with supersymmetry	PLB 76 (1978) 575
12	P. Ramond	Dual theory for free fermions	PRD 3 (1971) 2415
13	Y. A. Golfand and E. P. Likhtman	Extension of the algebra of Poincar$ \'e $ group generators and violation of p invariance	JEPTL 13 (1971)323
14	A. Neveu and J. H. Schwarz	Factorizable dual model of pions	NPB 31 (1971) 86
15	D. V. Volkov and V. P. Akulov	Possible universal neutrino interaction	JEPTL 16 (1972)438
16	J. Wess and B. Zumino	A Lagrangian model invariant under supergauge transformations	PLB 49 (1974) 52
17	J. Wess and B. Zumino	Supergauge transformations in four dimensions	NPB 70 (1974) 39
18	P. Fayet	Supergauge invariant extension of the Higgs mechanism and a model for the electron and its neutrino	NPB 90 (1975) 104
19	H. P. Nilles	Supersymmetry, supergravity and particle physics	PR 110 (1984) 1
20	R. Barbier et al.	R-parity violating supersymmetry	PR 420 (2005) 1	hep-ph/0406039
21	BaBar Collaboration	Evidence for an excess of $ \bar{B} \to D^{(*)} \tau^-\bar{\nu}_\tau $ decays	PRL 109 (2012) 101802	1205.5442
22	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) 072012	1303.0571
23	Belle Collaboration	Observation of $ B^0 \to D^{*-} \tau^+ \nu_\tau $ decay at Belle	PRL 99 (2007) 191807	0706.4429
24	Belle Collaboration	Observation of $ B^+ \to \bar{D}^{*0} \tau^+ \nu_\tau $ and evidence for $ B^+ \to \bar{D}^0 \tau^+ \nu_\tau $ at Belle	PRD 82 (2010) 072005	1005.2302
25	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) 072014	1507.03233
26	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
27	LHCb Collaboration	Measurement of form-factor-independent observables in the decay $ B^{0} \to K^{*0} \mu^+ \mu^- $	PRL 111 (2013) 191801	1308.1707
28	LHCb Collaboration	Test of lepton universality using $ B^{+}\rightarrow K^{+}\ell^{+}\ell^{-} $ decays	PRL 113 (2014) 151601	1406.6482
29	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
30	LHCb Collaboration	Angular analysis of the $ B^{0} \to K^{*0} \mu^{+} \mu^{-} $ decay using 3 fb$ ^{-1} $ of integrated luminosity	JHEP 02 (2016) 104	1512.04442
31	LHCb Collaboration	Test of lepton universality with $ B^{0} \rightarrow K^{*0}\ell^{+}\ell^{-} $ decays	JHEP 08 (2017) 055	1705.05802
32	M. Tanaka and R. Watanabe	New physics in the weak interaction of $ \bar B\to D^{(*)}\tau\bar\nu $	PRD 87 (2013) 034028	1212.1878
33	Y. Sakaki, M. Tanaka, A. Tayduganov, and R. Watanabe	Testing leptoquark models in $ \bar B \to D^{(*)} \tau \bar\nu $	PRD 88 (2013) 094012	1309.0301
34	I. Dor\vsner, S. Fajfer, N. Ko\vsnik, and I. Ni\vsand\vzi\'c	Minimally flavored colored scalar in $ \bar B \to D^{(*)} \tau \bar \nu $ and the mass matrices constraints	JHEP 11 (2013) 084	1306.6493
35	B. Gripaios, M. Nardecchia, and S. A. Renner	Composite leptoquarks and anomalies in $ B $-meson decays	JHEP 05 (2015) 006	1412.1791
36	M. Bauer and M. Neubert	Minimal leptoquark explanation for the R$ _{D^{(*)}} $ , R$ _K $ , and $ (g-2)_\mu $ anomalies	PRL 116 (2016) 141802	1511.01900
37	D. Buttazzo, A. Greljo, G. Isidori, and D. Marzocca	B-physics anomalies: a guide to combined explanations	JHEP 11 (2017) 044	1706.07808
38	I. Dor\vsner and A. Greljo	Leptoquark toolbox for precision collider studies		1801.07641
39	B. Diaz, M. Schmaltz, and Y.-M. Zhong	The leptoquark hunter's guide: Pair production	JHEP 10 (2017) 097	1706.05033
40	ATLAS Collaboration	Searches for scalar leptoquarks in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector	EPJC 76 (2016) 5	1508.04735
41	CMS Collaboration	Search for third-generation scalar leptoquarks decaying to a top quark and a $ \tau $ lepton at $ \sqrt{s} = $ 13 TeV	Submitted to \it EPJC	CMS-B2G-16-028 1803.02864
42	CMS Collaboration	Search for pair production of first and second generation leptoquarks in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	PRD 93 (2016) 032004	CMS-EXO-12-041 1509.03744
43	CMS Collaboration	Search for pair production of third-generation scalar leptoquarks and top squarks in proton-proton collisions at $ \sqrt{s} = $ 8 TeV	PLB 739 (2014) 229	CMS-EXO-12-032 1408.0806
44	H1 Collaboration	Search for first generation leptoquarks in $ ep $ collisions at HERA	PLB 704 (2011) 388	1107.3716
45	ZEUS Collaboration	Search for first-generation leptoquarks at HERA	PRD 86 (2012) 012005	1205.5179
46	ATLAS Collaboration	Search for third generation scalar leptoquarks in pp collisions at $ \sqrt{s} = $ 7 TeV with the ATLAS detector	JHEP 06 (2013) 033	1303.0526
47	CMS Collaboration	Search for third-generation scalar leptoquarks and heavy right-handed neutrinos in final states with two tau leptons and two jets in proton-proton collisions at $ \sqrt{s}= $ 13 TeV	JHEP 07 (2017) 121	CMS-EXO-16-023 1703.03995
48	C. G. Lester and D. J. Summers	Measuring masses of semi-invisibly decaying particles pair produced at hadron colliders	PLB 463 (1999) 99	hep-ph/9906349
49	CMS Collaboration	Search for new phenomena with the $ M_{\mathrm {T2}} $ variable in the all-hadronic final state produced in proton-proton collisions at $ \sqrt{s} = $ 13 TeV	EPJC 77 (2017) 710	CMS-SUS-16-036 1705.04650
50	CMS Collaboration	The CMS experiment at the CERN LHC	JINST 3 (2008) S08004	CMS-00-001
51	CMS Collaboration	Particle-flow reconstruction and global event description with the CMS detector	JINST 12 (2017) P10003	CMS-PRF-14-001 1706.04965
52	M. Cacciari, G. P. Salam, and G. Soyez	The anti-$ {k_{\mathrm{T}}} $ jet clustering algorithm	JHEP 04 (2008) 063	0802.1189
53	M. Cacciari, G. P. Salam, and G. Soyez	FastJet user manual	EPJC 72 (2012) 1896	1111.6097
54	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
55	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
56	NNPDF Collaboration	Parton distributions for the LHC run II	JHEP 04 (2015) 040	1410.8849
57	T. Sjostrand et al.	An introduction to PYTHIA 8.2	CPC 191 (2015) 159	1410.3012
58	CMS Collaboration	Event generator tunes obtained from underlying event and multiparton scattering measurements	EPJC 76 (2016) 155	CMS-GEN-14-001 1512.00815
59	J. Alwall et al.	Comparative study of various algorithms for the merging of parton showers and matrix elements in hadronic collisions	EPJC 53 (2008) 473	0706.2569
60	GEANT4 Collaboration	GEANT4 -- a simulation toolkit	NIMA 506 (2003) 250
61	CMS Collaboration	The fast simulation of the CMS detector at LHC	J. Phys. Conf. Ser. 331 (2011) 032049
62	N. Arkani-Hamed et al.	MARMOSET: The path from LHC data to the new standard model via on-shell effective theories		hep-ph/0703088
63	J. Alwall, P. C. Schuster, and N. Toro	Simplified models for a first characterization of new physics at the LHC	PRD 79 (2009) 075020	0810.3921
64	J. Alwall, M.-P. Le, M. Lisanti, and J. G. Wacker	Model-independent jets plus missing energy searches	PRD 79 (2009) 015005	0809.3264
65	D. Alves et al.	Simplified models for LHC new physics searches	JPG 39 (2012) 105005	1105.2838
66	CMS Collaboration	Interpretation of searches for supersymmetry with simplified models	PRD 88 (2013) 052017	CMS-SUS-11-016 1301.2175
67	NNPDF Collaboration	Parton distributions with LHC data	NPB 867 (2013) 244	1207.1303
68	NNPDF Collaboration	Parton distributions from high-precision collider data	EPJC 77 (2017) 663	1706.00428
69	T. Junk	Confidence level computation for combining searches with small statistics	NIMA 434 (1999) 435	hep-ex/9902006
70	A. L. Read	Presentation of search results: the CL$ _{\text{s}} $ technique	in Durham IPPP Workshop: Advanced Statistical Techniques in Particle Physics, p. 2693 Durham, UK, March, 2002 [JPG 28 (2002) 2693]
71	G. Cowan, K. Cranmer, E. Gross, and O. Vitells	Asymptotic formulae for likelihood-based tests of new physics	EPJC 71 (2011) 1554	1007.1727
72	ATLAS and CMS Collaborations	Procedure for the LHC Higgs boson search combination in summer 2011	CMS-NOTE-2011-005
73	CMS Collaboration	CMS luminosity measurements for the 2016 data taking period	CMS-PAS-LUM-17-001	CMS-PAS-LUM-17-001