CMS logoCMS event Hgg
Compact Muon Solenoid
LHC, CERN

CMS-PAS-SUS-18-001
Constraints on models of scalar and vector leptoquarks decaying to a quark and a neutrino at $\sqrt{s}= $ 13 TeV
Abstract: Many searches for Supersymmetry at the CERN LHC are sensitive to other scenarios of physics beyond the standard model. In this note, the results of a previous search for squarks and gluinos are re-interpreted to constrain models of leptoquark production. Pair production is considered, and both leptoquarks are assumed to decay to a quark and a neutrino. The search selects 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$^{-1}$. Compared to previous CMS results, both scalar and vector leptoquarks are considered, as well as higher leptoquark mass values, and for the first time, leptoquark decays to a light quark (any single one of u, d, s, or c) and a neutrino are considered. Assuming scalar (vector) leptoquarks decaying with unity branching fraction to a light quark and neutrino, masses below 980 (1790) GeV are excluded by the observed data. For leptoquarks decaying to a bottom quark and a neutrino, masses below 1100 (1810) GeV are excluded, while assuming decays to a top quark and a neutrino, masses below 1020 (1780) GeV are excluded. Vector leptoquarks decaying with a 50% branching fraction to a top quark and a neutrino, and 50% to a bottom quark and tau lepton, have been proposed as an explanation of anomalous flavor physics results. In such a model, we exclude leptoquarks with masses below 1530 GeV, placing the most stringent constraint to date.
Figures Summary References CMS Publications
Figures

png pdf
Figure 1:
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 unity branching fraction to $ {\mathrm {t}} {\nu} $. 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 sources. The lower pane of each plot shows the ratio of observed data over predicted background. The categories require $ {H_{\mathrm {T}}} > $ 1500 GeV, 4-6 jets, and (left) exactly one b-tagged jet or (right) exactly two b-tagged jets.

png pdf
Figure 1-a:
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 unity branching fraction to $ {\mathrm {t}} {\nu} $. 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 sources. The lower pane of each plot shows the ratio of observed data over predicted background. The categories require $ {H_{\mathrm {T}}} > $ 1500 GeV, 4-6 jets, and (left) exactly one b-tagged jet or (right) exactly two b-tagged jets.

png pdf
Figure 1-b:
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 unity branching fraction to $ {\mathrm {t}} {\nu} $. 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 sources. The lower pane of each plot shows the ratio of observed data over predicted background. The categories require $ {H_{\mathrm {T}}} > $ 1500 GeV, 4-6 jets, and (left) exactly one b-tagged jet or (right) exactly two b-tagged jets.

png pdf
Figure 2:
The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with unity branching fraction to a neutrino and: (upper left) a light quark (one of u, d, s, or c), (upper right) a bottom quark, and (lower) a top quark. The solid black line represents the observed exclusion. The dashed black line represents the median expected exclusion. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The blue lines show the theoretical cross section for scalar LQ pair production with its uncertainty, and the red lines show the same for vector LQ pair production. (lower) Also shown in magenta is the product of the theoretical cross section and the square of the branching fraction, for vector LQ pair production assuming a 50% branching fraction to a top quark and a neutrino.

png pdf
Figure 2-a:
The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with unity branching fraction to a neutrino and: (upper left) a light quark (one of u, d, s, or c), (upper right) a bottom quark, and (lower) a top quark. The solid black line represents the observed exclusion. The dashed black line represents the median expected exclusion. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The blue lines show the theoretical cross section for scalar LQ pair production with its uncertainty, and the red lines show the same for vector LQ pair production. (lower) Also shown in magenta is the product of the theoretical cross section and the square of the branching fraction, for vector LQ pair production assuming a 50% branching fraction to a top quark and a neutrino.

png pdf
Figure 2-b:
The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with unity branching fraction to a neutrino and: (upper left) a light quark (one of u, d, s, or c), (upper right) a bottom quark, and (lower) a top quark. The solid black line represents the observed exclusion. The dashed black line represents the median expected exclusion. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The blue lines show the theoretical cross section for scalar LQ pair production with its uncertainty, and the red lines show the same for vector LQ pair production. (lower) Also shown in magenta is the product of the theoretical cross section and the square of the branching fraction, for vector LQ pair production assuming a 50% branching fraction to a top quark and a neutrino.

png pdf
Figure 2-c:
The 95% CL upper limits on the production cross sections as a function of LQ mass for LQ pair production decaying with unity branching fraction to a neutrino and: (upper left) a light quark (one of u, d, s, or c), (upper right) a bottom quark, and (lower) a top quark. The solid black line represents the observed exclusion. The dashed black line represents the median expected exclusion. The inner (green) band and the outer (yellow) band indicate the regions containing 68 and 95%, respectively, of the distribution of limits expected under the background-only hypothesis. The blue lines show the theoretical cross section for scalar LQ pair production with its uncertainty, and the red lines show the same for vector LQ pair production. (lower) Also shown in magenta is the product of the theoretical cross section and the square of the branching fraction, for vector LQ pair production assuming a 50% branching fraction to a top quark and a neutrino.
Summary
The CMS search for jets and missing transverse momentum using the $ {M_{\mathrm{T2}}} $ variable has been re-interpreted to place limits on leptoquark (LQ) pair production, where the LQ decays with unity 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$^{-1}$. Compared to previous CMS results, both scalar and vector leptoquarks are considered, as well as higher leptoquark mass values, and for the first time, leptoquark decays to a light quark (any single one of u, d, s, or c) and a neutrino are considered. Assuming that there is only one LQ state within mass reach of the LHC, for scalar (vector) leptoquarks decaying to a light quark and a neutrino, masses below 980 (1790) GeV have been excluded by the observed data, corresponding to a pair production cross section of 0.0059 (0.0011) pb. For leptoquarks decaying to a bottom quark and a neutrino, masses below 1100 (1810) GeV have been excluded, corresponding to a cross section of 0.0024 (0.0010) pb, while assuming decays to a top quark and a neutrino, masses below 1020 (1780) GeV have been excluded, corresponding to a cross section of 0.0043 (0.0012) pb. In the model of Refs. [23,24], a vector leptoquark with 50% branching fraction to a top quark and a neutrino is predicted. We exclude masses below 1530 GeV for such a state with our observed data, providing the strongest constraint to date in this model. At high LQ mass values, these results improve the upper limits on LQ pair production cross sections by as much as a factor of 2.8 over the extrapolation assumed in Ref. [45].
References
1 W. Buchmuller, R. Ruckl, and D. Wyler Leptoquarks in lepton-quark collisions PLB 191 (1987) 442, . [Erratum: \DOI10.1016/S0370-2693(99)00014-3]
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 E. Farhi and L. Susskind Technicolor PR 74 (1981) 277
6 K. D. Lane and M. V. Ramana Walking technicolor signatures at hadron colliders PRD 44 (1991) 2678
7 B. Schrempp and F. Schrempp Light leptoquarks PLB 153 (1985) 101
8 B. Gripaios Composite leptoquarks at the LHC JHEP 02 (2010) 045 0910.1789
9 G. R. Farrar and P. Fayet Phenomenology of the production, decay, and detection of new hadronic states associated with supersymmetry PLB 76 (1978) 575
10 P. Ramond Dual theory for free fermions PRD 3 (1971) 2415
11 Y. A. Gol'fand and E. P. Likhtman Extension of the algebra of Poincare group generators and violation of P invariance JEPTL 13 (1971)323
12 A. Neveu and J. H. Schwarz Factorizable dual model of pions NPB 31 (1971) 86
13 D. V. Volkov and V. P. Akulov Possible universal neutrino interaction JEPTL 16 (1972)438
14 J. Wess and B. Zumino A lagrangian model invariant under supergauge transformations PLB 49 (1974) 52
15 J. Wess and B. Zumino Supergauge transformations in four dimensions NPB 70 (1974) 39
16 P. Fayet Supergauge invariant extension of the Higgs mechanism and a model for the electron and its neutrino NPB 90 (1975) 104
17 H. P. Nilles Supersymmetry, supergravity and particle physics Phys. Rep. 110 (1984) 1
18 R. Barbier et al. R-parity violating supersymmetry PR 420 (2005) 1 hep-ph/0406039
19 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
20 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
21 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
22 B. Gripaios, M. Nardecchia, and S. A. Renner Composite leptoquarks and anomalies in $ B $-meson decays JHEP 05 (2015) 006 1412.1791
23 D. Buttazzo, A. Greljo, G. Isidori, and D. Marzocca B-physics anomalies: a guide to combined explanations JHEP 11 (2017) 044 1706.07808
24 I. Dor\vsner and A. Greljo Leptoquark toolbox for precision collider studies 1801.07641
25 BaBar Collaboration Evidence for an excess of $ \bar{B} \to D^{(*)} \tau^-\bar{\nu}_\tau $ decays PRL 109 (2012) 101802 1205.5442
26 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
27 Belle Collaboration Observation of $ B^0 \to D^{*-} \tau^+ \nu_\tau $ decay at Belle PRL 99 (2007) 191807 0706.4429
28 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
29 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
30 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), no. 21, 211801 1612.00529
31 LHCb Collaboration Measurement of Form-Factor-Independent Observables in the Decay $ B^{0} \to K^{*0} \mu^+ \mu^- $ PRL 111 (2013) 191801 1308.1707
32 LHCb Collaboration Test of lepton universality using $ B^{+}\rightarrow K^{+}\ell^{+}\ell^{-} $ decays PRL 113 (2014) 151601 1406.6482
33 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
34 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
35 LHCb Collaboration Test of lepton universality with $ B^{0} \rightarrow K^{*0}\ell^{+}\ell^{-} $ decays JHEP 08 (2017) 055 1705.05802
36 ATLAS Collaboration Search for scalar leptoquarks in pp collisions at $ \sqrt{s} = $ 13 TeV with the ATLAS experiment New J. Phys. 18 (2016) 093016 1605.06035
37 ATLAS Collaboration Searches for scalar leptoquarks in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector EPJC 76 (2016) 5 1508.04735
38 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
39 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
40 CMS Collaboration Search for heavy neutrinos or third-generation leptoquarks in final states with two hadronically decaying $ \tau $ leptons and two jets in proton-proton collisions at $ \sqrt{s}= $ 13 TeV JHEP 03 (2017) 077 CMS-EXO-16-016
1612.01190
41 CMS Collaboration Search for single production of scalar leptoquarks in proton-proton collisions at $ \sqrt{s} = $ 8 TeV PRD 93 (2016) 032005 CMS-EXO-12-043
1509.03750
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 Third-Generation Scalar Leptoquarks in the t$ \tau $ Channel in Proton-Proton Collisions at $ \sqrt{s} = $ 8 TeV JHEP 07 (2015) 042 CMS-EXO-14-008
1503.09049
44 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
45 B. Diaz, M. Schmaltz, and Y.-M. Zhong The leptoquark Hunter’s guide: Pair production JHEP 10 (2017) 097 1706.05033
46 ATLAS Collaboration Search for squarks and gluinos in final states with jets and missing transverse momentum using 36 fb$ ^{-1} $ of $ \sqrt{s} = 13 TeV pp $ collision data with the ATLAS detector Submitted to \it PRD 1712.02332
47 ATLAS Collaboration Search for supersymmetry in events with $ b $-tagged jets and missing transverse momentum in $ pp $ collisions at $ \sqrt{s}= $ 13 TeV with the ATLAS detector JHEP 11 (2017) 195 1708.09266
48 ATLAS Collaboration Search for a scalar partner of the top quark in the jets plus missing transverse momentum final state at $ \sqrt{s} = $ 13 TeV with the ATLAS detector JHEP 12 (2017) 085 1709.04183
49 ATLAS Collaboration Search for top-squark pair production in final states with one lepton, jets, and missing transverse momentum using 36 fb$ ^{-1} $ of $ \sqrt{s}= $ 13 TeV pp collision data with the ATLAS detector Submitted to \it JHEP 1711.11520
50 ATLAS Collaboration Search for direct top squark pair production in final states with two leptons in $ \sqrt{s} = 13 TeV pp $ collisions with the ATLAS detector EPJC 77 (2017) 898 1708.03247
51 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
52 CMS Collaboration Search for supersymmetry in multijet events with missing transverse momentum in proton-proton collisions at 13 TeV PRD 96 (2017) 032003 CMS-SUS-16-033
1704.07781
53 CMS Collaboration Search for direct production of supersymmetric partners of the top quark in the all-jets final state in proton-proton collisions at $ \sqrt{s}= $ 13 TeV JHEP 10 (2017) 005 CMS-SUS-16-049
1707.03316
54 CMS Collaboration Search for top squark pair production in pp collisions at $ \sqrt{s}= $ 13 TeV using single lepton events JHEP 10 (2017) 019 CMS-SUS-16-051
1706.04402
55 CMS Collaboration Search for top squarks and dark matter particles in opposite-charge dilepton final states at $ \sqrt{s}= $ 13 TeV Submitted to \it PRD CMS-SUS-17-001
1711.00752
56 CMS Collaboration Search for the pair production of third-generation squarks with two-body decays to a bottom or charm quark and a neutralino in proton-proton collisions at sqrt(s) = 13 TeV Submitted to \it PLB CMS-SUS-16-032
1707.07274
57 CMS Collaboration Search for supersymmetry in proton-proton collisions at 13 TeV using identified top quarks Submitted to \it PRD CMS-SUS-16-050
1710.11188
58 C. G. Lester and D. J. Summers Measuring masses of semiinvisibly decaying particles pair produced at hadron colliders PLB 463 (1999) 99 hep-ph/9906349
59 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004 CMS-00-001
60 M. Cacciari, G. P. Salam, and G. Soyez The anti-$ k_t $ jet clustering algorithm JHEP 04 (2008) 063 0802.1189
61 M. Cacciari, G. P. Salam, and G. Soyez FastJet user manual EPJC 72 (2012) 1896 1111.6097
62 CMS Collaboration Identification of heavy-flavour jets with the CMS detector in pp collisions at 13 TeV Submitted to \it JINST CMS-BTV-16-002
1712.07158
63 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
64 NNPDF Collaboration Parton distributions for the LHC Run II JHEP 04 (2015) 040 1410.8849
65 T. Sjostrand, S. Mrenna, and P. Z. Skands A brief introduction to PYTHIA 8.1 CPC 178 (2008) 852 0710.3820
66 CMS Collaboration Event generator tunes obtained from underlying event and multiparton scattering measurements EPJC 76 (2016) 155 CMS-GEN-14-001
1512.00815
67 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
68 S. Abdullin et al. The fast simulation of the CMS detector at LHC J. Phys. Conf. Ser. 331 (2011) 032049
69 N. Arkani-Hamed et al. MARMOSET: The Path from LHC Data to the New Standard Model via On-Shell Effective Theories hep-ph/0703088
70 J. Alwall, P. Schuster, and N. Toro Simplified models for a first characterization of new physics at the LHC PRD 79 (2009) 075020 0810.3921
71 J. Alwall, M.-P. Le, M. Lisanti, and J. G. Wacker Model-independent jets plus missing energy searches PRD 79 (2009) 015005 0809.3264
72 D. Alves et al. Simplified models for LHC new physics searches JPG 39 (2012) 105005 1105.2838
73 CMS Collaboration Interpretation of searches for supersymmetry with simplified models PRD 88 (2013) 052017 CMS-SUS-11-016
1301.2175
74 NNPDF Collaboration Parton distributions with LHC data NPB 867 (2013) 244 1207.1303
75 NNPDF Collaboration Parton distributions from high-precision collider data EPJC 77 (2017) 663 1706.00428
Compact Muon Solenoid
LHC, CERN