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| CMS-PAS-B2G-16-027 | ||
| Search for leptoquarks coupling to third generation quarks | ||
| CMS Collaboration | ||
| June 2018 | ||
| Abstract: Three of the most significant measured deviations from standard model predictions, the anomalous magnetic moment of the muon, the enhanced decay rate $\overline{B}\to D^{(*)} \tau \overline{\nu}$ and hints of lepton universality violation in $\overline{B}\to \overline{K} \ell^+ \ell^-$ decays, can be explained through the existence of leptoquarks with large couplings to third generation quarks and masses at the TeV scale. These states can be probed at the CERN LHC in high energy pp collisions. A first search is presented for the pair production of leptoquarks coupling to a top quark and a muon using data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 35.9 fb$^{-1}$ as recorded by the CMS experiment. Combined with previous results for leptoquark decays into $\mathrm{t}\tau$ and $\mathrm{b}\nu$, this search allows for the first time to cover the full allowed parameter space of leptoquark couplings to third generation quarks. Scalar leptoquarks decaying exclusively into $\mathrm{t}\mu$, $\mathrm{t}\tau$ and $\mathrm{b}\nu$ can be excluded up to masses of 1420, 900 and 1080 GeV, respectively. Leptoquarks can be excluded up to masses of 900 GeV for all possible combinations of branching fractions to these final states. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRL 121, 241802 (2018). The superseded preliminary plots can be found here. |
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| Figures | |
png pdf |
Figure 1:
Post-fit distributions for $M_{\mathrm {LQ}}^{\text {rec}}$ (category A, left) and $S_{\mathrm {T}}$ (category B, right) after applying the full selection and estimating the $\mathrm{t \bar{t}}+$ DY+jets background contribution from data in category B. All backgrounds are normalised according to the post-fit nuisance parameters based on the corresponding SM cross sections. In the upper parts the dashed areas correspond to the total uncertainty. In the lower parts, the dark grey and light grey bands indicate the statistical and the total uncertainty, respectively. |
png pdf |
Figure 1-a:
Post-fit distributions for $M_{\mathrm {LQ}}^{\text {rec}}$ (category A, left) and $S_{\mathrm {T}}$ (category B, right) after applying the full selection and estimating the $\mathrm{t \bar{t}}+$ DY+jets background contribution from data in category B. All backgrounds are normalised according to the post-fit nuisance parameters based on the corresponding SM cross sections. In the upper parts the dashed areas correspond to the total uncertainty. In the lower parts, the dark grey and light grey bands indicate the statistical and the total uncertainty, respectively. |
png pdf |
Figure 1-b:
Post-fit distributions for $M_{\mathrm {LQ}}^{\text {rec}}$ (category A, left) and $S_{\mathrm {T}}$ (category B, right) after applying the full selection and estimating the $\mathrm{t \bar{t}}+$ DY+jets background contribution from data in category B. All backgrounds are normalised according to the post-fit nuisance parameters based on the corresponding SM cross sections. In the upper parts the dashed areas correspond to the total uncertainty. In the lower parts, the dark grey and light grey bands indicate the statistical and the total uncertainty, respectively. |
png pdf |
Figure 2:
Observed upper limits on the production cross section for pair production of LQs decaying into a top quark and a muon or a $\tau $ lepton (left) and LQs decaying into a top quark and a muon or into a $ {\mathrm {b}}$ quark and a neutrino (right) at 95% CL in the $M_{LQ} - \mathcal {B}(\mathrm {LQ}\to {\mathrm {t}}\mu)$ plane. The solid and dashed lines show the observed and expected mass exclusion limits while the dotted lines indicate the 68% CL region of the expected mass exclusion limit. The mass limit is derived by using the prediction for the LQ signal calculated at NLO [31]. |
png pdf |
Figure 2-a:
Observed upper limits on the production cross section for pair production of LQs decaying into a top quark and a muon or a $\tau $ lepton (left) and LQs decaying into a top quark and a muon or into a $ {\mathrm {b}}$ quark and a neutrino (right) at 95% CL in the $M_{LQ} - \mathcal {B}(\mathrm {LQ}\to {\mathrm {t}}\mu)$ plane. The solid and dashed lines show the observed and expected mass exclusion limits while the dotted lines indicate the 68% CL region of the expected mass exclusion limit. The mass limit is derived by using the prediction for the LQ signal calculated at NLO [31]. |
png pdf |
Figure 2-b:
Observed upper limits on the production cross section for pair production of LQs decaying into a top quark and a muon or a $\tau $ lepton (left) and LQs decaying into a top quark and a muon or into a $ {\mathrm {b}}$ quark and a neutrino (right) at 95% CL in the $M_{LQ} - \mathcal {B}(\mathrm {LQ}\to {\mathrm {t}}\mu)$ plane. The solid and dashed lines show the observed and expected mass exclusion limits while the dotted lines indicate the 68% CL region of the expected mass exclusion limit. The mass limit is derived by using the prediction for the LQ signal calculated at NLO [31]. |
| Tables | |
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Table 1:
Prior systematic uncertainties in the SM backgrounds and signal. |
| Summary |
| References | ||||
| 1 | BaBar Collaboration | Evidence for an excess of $ \bar{B} \to D^{(*)} \tau^-\bar{\nu}_\tau $ decays | PRL 109 (2012) 101802 | 1205.5442 |
| 2 | 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), no. 7, 072012 | 1303.0571 |
| 3 | Belle Collaboration | Observation of $ B^0 \rightarrow D^{*-} \tau^+ \nu_{\tau} $ decay at Belle | PRL 99 (2007) 191807 | 0706.4429 |
| 4 | Belle Collaboration | Observation of $ B^+ \rightarrow \bar{D}^{*0} \tau^+ \nu_{\tau} $ and evidence for $ B^+ \rightarrow \bar{D}^0 \tau^+ \nu_{\tau} $ at Belle | PRD 82 (2010) 072005 | 1005.2302 |
| 5 | 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), no. 7, 072014 | 1507.03233 |
| 6 | LHCb Collaboration | Differential branching fraction and angular analysis of the decay $ B^{0} \to K^{*0} \mu^{+}\mu^{-} $ | JHEP 08 (2013) 131 | 1304.6325 |
| 7 | LHCb Collaboration | Measurement of form-factor-independent observables in the decay $ B^{0} \to K^{*0} \mu^+ \mu^- $ | PRL 111 (2013) 191801 | 1308.1707 |
| 8 | LHCb Collaboration | Test of lepton universality using $ B^{+}\to K^{+}\ell^{+}\ell^{-} $ decays | PRL 113 (2014) 151601 | 1406.6482 |
| 9 | 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), no. 11, 111803 | 1506.08614 |
| 10 | HFLAV Collaboration | Averages of $ b $-hadron, $ c $-hadron, and $ \tau $-lepton properties as of summer 2016 | EPJC 77 (2017) 895 | 1612.07233 |
| 11 | Muon g-2 Collaboration | Final report of the muon E821 anomalous magnetic moment measurement at BNL | PRD 73 (2006) 072003 | hep-ex/0602035 |
| 12 | M. Davier, A. Hoecker, B. Malaescu, and Z. Zhang | Reevaluation of the hadronic vacuum polarisation contributions to the standard model predictions of the muon $ g-2 $ and $ {\alpha (m_z^2)} $ using newest hadronic cross-section data | EPJC 77 (2017) 827 | 1706.09436 |
| 13 | 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 |
| 14 | 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 |
| 15 | I. Dor$\text\us$ner, S. Fajfer, N. Ko$\text\us$nik, and I. Ni$\text\us$and$\text\vz$i\'c | Minimally flavored colored scalar in $ \bar B \to D^{(*)} \tau \bar \nu $ and the mass matrices constraints | JHEP 11 (2013) 084 | 1306.6493 |
| 16 | B. Dumont, K. Nishiwaki, and R. Watanabe | LHC constraints and prospects for $ S_1 $ scalar leptoquark explaining the $ \bar B \to D^{(*)} \tau \bar\nu $ anomaly | PRD 94 (2016) 034001 | 1603.05248 |
| 17 | B. Gripaios, M. Nardecchia, and S. A. Renner | Composite leptoquarks and anomalies in $ b $-meson decays | JHEP 05 (2015) 006 | 1412.1791 |
| 18 | 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 |
| 19 | E. Coluccio Leskow, G. D'Ambrosio, A. Crivellin, and D. Muller | $ (g-2)_\mu $, lepton flavor violation, and $ Z $ decays with leptoquarks: Correlations and future prospects | PRD 95 (2017) 055018 | 1612.06858 |
| 20 | D. Be$\text\uc$irevi\'c and O. Sumensari | A leptoquark model to accommodate $ R_K^\mathrm{exp} < R_K^\mathrm{SM} $ and $ R_{K^\ast}^\mathrm{exp} < R_{K^\ast}^\mathrm{SM} $ | JHEP 08 (2017) 104 | 1704.05835 |
| 21 | G. Hiller and I. Nisandzic | $ R_K $ and $ R_{K^{\ast}} $ beyond the standard model | PRD 96 (2017) 035003 | 1704.05444 |
| 22 | J. C. Pati and A. Salam | Lepton number as the fourth color | PRD 10 (1974) 275, .[Erratum: Phys. Rev. D11, 703 (1975)] | |
| 23 | H. Georgi and S. L. Glashow | Unity of all elementary-particle forces | PRL 32 (1974) 438 | |
| 24 | H. Fritzsch and P. Minkowski | Unified interactions of leptons and hadrons | Annals Phys. 93 (1975) 193 | |
| 25 | E. Farhi and L. Susskind | Technicolor | PR 74 (1981) 277 | |
| 26 | K. Lane and M. V. Ramana | Walking technicolor signatures at hadron colliders | PRD 44 (1991) 2678 | |
| 27 | B. Schrempp and F. Schrempp | Light leptoquarks | PLB 153 (1985) 101 | |
| 28 | B. Gripaios | Composite leptoquarks at the LHC | JHEP 02 (2010) 045 | 0910.1789 |
| 29 | W. Buchm$\textu$ller, R. R$\textu$ckl, and D. Wyler | Leptoquarks in lepton - quark collisions | PLB 191 (1987) 442, .[Erratum: Phys. Lett. B 448, 320 (1999)] | |
| 30 | D. E. Acosta and S. K. Blessing | Leptoquark searches at HERA and the Tevatron | Ann. Rev. Nucl. Part. Sci. 49 (1999) 389 | |
| 31 | M. Kramer, T. Plehn, M. Spira, and P. M. Zerwas | Pair production of scalar leptoquarks at the CERN LHC | PRD 71 (2005) 057503 | hep-ph/0411038 |
| 32 | 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 |
| 33 | D0 Collaboration | Search for third-generation leptoquarks in $ \mathrm{p} \bar{\mathrm{p}} $ collisions at $ \sqrt{s} = $ 1.96 TeV | PRL 99 (2007) 061801 | 0705.0812 |
| 34 | CDF Collaboration | Search for third generation vector leptoquarks in $ \mathrm{p}\bar{\mathrm{p}} $ collisions at $ \sqrt{s} = $ 1.96 TeV | PRD 77 (2008) 091105 | 0706.2832 |
| 35 | 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 |
| 36 | CMS Collaboration | Search for third-generation leptoquarks and scalar bottom quarks in $ pp $ collisions at $ \sqrt{s}= $ 7 TeV | JHEP 12 (2012) 055 | CMS-EXO-11-030 1210.5627 |
| 37 | 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 |
| 38 | CMS Collaboration | Searches for third-generation squark production in fully hadronic final states in proton-proton collisions at $ \sqrt{s} = $ 8 TeV | JHEP 06 (2015) 116 | CMS-SUS-14-001 1503.08037 |
| 39 | ATLAS Collaboration | Searches for scalar leptoquarks in pp collisions at $ \sqrt{s} = $ 8 TeV with the ATLAS detector | EPJC 76 (2016) 5 | 1508.04735 |
| 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 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 |
| 42 | 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 |
| 43 | CMS Collaboration | Search for third-generation scalar leptoquarks decaying to a top quark and a $ \tau $ lepton at $ \sqrt{s}= $ 13 TeV | CMS-B2G-16-028 1803.02864 |
|
| 44 | CMS Collaboration | The CMS experiment at the CERN LHC | JINST 3 (2008) S08004 | CMS-00-001 |
| 45 | CMS Collaboration | The CMS trigger system | JINST 12 (2017) P01020 | CMS-TRG-12-001 1609.02366 |
| 46 | T. Sj$\texto$strand et al. | An introduction to PYTHIA 8.2 | CPC 191 (2015) 159 | 1410.3012 |
| 47 | P. Nason | A new method for combining NLO QCD with shower Monte Carlo algorithms | JHEP 11 (2004) 040 | hep-ph/0409146 |
| 48 | S. Frixione, P. Nason, and C. Oleari | Matching NLO QCD computations with parton shower simulations: the POWHEG method | JHEP 11 (2007) 070 | 0709.2092 |
| 49 | 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 |
| 50 | S. Frixione, P. Nason, and G. Ridolfi | A positive-weight next-to-leading-order Monte Carlo for heavy flavour hadroproduction | JHEP 09 (2007) 126 | 0707.3088 |
| 51 | T. Melia, P. Nason, R. Rontsch, and G. Zanderighi | W+W-, WZ and ZZ production in the POWHEG BOX | JHEP 11 (2011) 078 | 1107.5051 |
| 52 | 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 |
| 53 | E. Re | Single-top Wt-channel production matched with parton showers using the POWHEG method | EPJC 71 (2011) 1547 | 1009.2450 |
| 54 | 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 |
| 55 | R. Frederix and S. Frixione | Merging meets matching in MC@NLO | JHEP 12 (2012) 061 | 1209.6215 |
| 56 | 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 |
| 57 | NNPDF Collaboration | Parton distributions for the LHC run II | JHEP 04 (2015) 040 | 1410.8849 |
| 58 | CMS Collaboration | Investigations of the impact of the parton shower tuning in PYTHIA 8 in the modelling of $ \mathrm{t\overline{t}} $ at $ \sqrt{s}= $ 8 and 13 TeV | CMS-PAS-TOP-16-021 | CMS-PAS-TOP-16-021 |
| 59 | CMS Collaboration | Event generator tunes obtained from underlying event and multiparton scattering measurements | EPJC 76 (2016) 155 | CMS-GEN-14-001 1512.00815 |
| 60 | P. Skands, S. Carrazza, and J. Rojo | Tuning PYTHIA 8.1: the Monash 2013 Tune | EPJC 74 (2014) 3024 | 1404.5630 |
| 61 | GEANT4 Collaboration | GEANT4: A simulation toolkit | NIMA 506 (2003) 250 | |
| 62 | J. Allison et al. | GEANT4 developments and applications | IEEE Trans. Nucl. Sci. 53 (2006) 270 | |
| 63 | CMS Collaboration | Particle-flow reconstruction and global event description with the CMS detector | JINST 12 (2017) P10003 | CMS-PRF-14-001 1706.04965 |
| 64 | M. Cacciari, G. P. Salam, and G. Soyez | The anti-$ k_t $ jet clustering algorithm | JHEP 04 (2008) 063 | 0802.1189 |
| 65 | M. Cacciari, G. P. Salam, and G. Soyez | FastJet user manual | EPJC 72 (2012) 1896 | 1111.6097 |
| 66 | CMS Collaboration | Technical proposal for the phase-ii upgrade of the compact muon solenoid | CMS-PAS-TDR-15-002 | CMS-PAS-TDR-15-002 |
| 67 | 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 |
| 68 | CMS Collaboration Collaboration | CMS Luminosity Measurements for the 2016 Data Taking Period | CMS-PAS-LUM-17-001, CERN, Geneva | |
| 69 | CMS Collaboration | Measurement of the $ t\bar{t} $ production cross section using events in the e$ \mu $ final state in pp collisions at $ \sqrt{s} = $ 13 TeV | EPJC77 (2017) 172 | CMS-TOP-16-005 1611.04040 |
| 70 | CMS Collaboration | Measurement of inclusive W and Z boson production cross sections in pp collisions at $ \sqrt{s} = $ 8 TeV | PRL 112 (2014) 191802 | CMS-SMP-12-011 1402.0923 |
| 71 | CMS Collaboration | Cross section measurement of $ t $-channel single top quark production in pp collisions at $ \sqrt s = $ 13 TeV | PLB772 (2017) 752--776 | CMS-TOP-16-003 1610.00678 |
| 72 | N. Kidonakis | NNLL threshold resummation for top-pair and single-top production | Phys. Part. Nucl. 45 (2014), no. 4, 714--722 | 1210.7813 |
| 73 | CMS Collaboration | Observation of the associated production of a single top quark and a $ W $ boson in $ pp $ collisions at $ \sqrt s = $ 8 TeV | PRL 112 (2014), no. 23, 231802 | CMS-TOP-12-040 1401.2942 |
| 74 | T. Gehrmann et al. | $ W^+W^- $ production at hadron colliders in next to next to leading order QCD | PRL 113 (2014) 212001 | 1408.5243 |
| 75 | J. M. Campbell, R. K. Ellis, and C. Williams | Vector boson pair production at the LHC | JHEP 07 (2011) 018 | 1105.0020 |
| 76 | CMS Collaboration | Measurement of the WZ production cross section in pp collisions at $ \sqrt(s) = $ 13 TeV | PLB766 (2017) 268--290 | CMS-SMP-16-002 1607.06943 |
| 77 | CMS Collaboration | Measurement of the cross section for top quark pair production in association with a W or Z boson in proton-proton collisions at $ \sqrt{s} = $ 13 TeV | CMS-TOP-17-005 1711.02547 |
|
| 78 | J. Ott | |||
| 79 | A. O'Hagan and J. J. Forster | Kendall's advanced theory of statistics. Vol. 2B: Bayesian Inference | ||
| 80 | CMS Collaboration | Constraints on models of scalar and vector leptoquarks decaying to a quark and a neutrino at $ \sqrt{s}= $ 13 TeV | CMS-SUS-18-001 1805.10228 |
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Compact Muon Solenoid LHC, CERN |
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