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| 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 | ||
| CMS Collaboration | ||
| March 2018 | ||
| 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. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRD 98 (2018) 032005. The superseded preliminary plots can be found here. |
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| Figures | |
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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]. |
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