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Search for leptoquarks coupled to third-generation quarks in proton-proton collisions at $\sqrt{s}=$ 13 TeV

The CMS collaboration
Phys.Rev.Lett. 121 (2018) 241802, 2018

Abstract (data abstract)
Three of the most significant measured deviations from standard model predictions, the enhanced decay rate for $\mathrm{B}\to\mathrm{D}^{\ast}\tau\nu$, hints of lepton universality violation in $\mathrm{B}\to\mathrm{K}^{\ast}\ell\ell$ decays, and the anomalous magnetic moment of the muon, can be explained by the existence of leptoquarks (LQs) with large couplings to third-generation quarks and masses at the TeV scale. The existence of these states can be probed at the LHC in high energy proton-proton collisions. A novel search is presented for pair production of LQs coupled to a top quark and a muon using data at a center-of-mass energy of $13\,\mathrm{TeV}$, corresponding to an integrated luminosity of $35.9\,\mathrm{fb}^{-1}$, recorded by the CMS experiment. No deviation from the standard model prediction has been observed and scalar LQs decaying exclusively into $t\mu$ are excluded up to masses of $1420\,\mathrm{GeV}$. The results of this search are combined with those from previous searches for LQ decays into $t\tau$ and $b\nu$, which excluded scalar LQs below masses of $900$ and $1080\,\mathrm{GeV}$. Vector LQs are excluded up to masses of $1190\,\mathrm{GeV}$ for all possible combinations of branching fractions to $t\mu$, $t\tau$ and $b\nu$. With this analysis, all relevant couplings of LQs with an electric charge of $-1/3$ to third-generation quarks are probed for the first time.

  • Figure 1a

    Contents of Figure 1 (left)

    10.17182/hepdata.85765.v1/t1

    Distributions for $M_{LQ}^{rec}$ (category A) after applying the full selection. All backgrounds are normalized according to the post-fit nuisance parameters...

  • Figure 1b

    Contents of Figure 1 (right)

    10.17182/hepdata.85765.v1/t2

    Distributions for $S_{T}$ (category B) after applying the full selection and estimating the $t\overline{t}$ and DY+jets background contributions from data...

  • Figure 2a (2-d limit)

    Contents of Figure 2 (left)

    10.17182/hepdata.85765.v1/t3

    Observed upper limits on the production cross section for pair production of LQs decaying into a top quark and a...

  • Figure 2a (mass exclusion limits)

    Contents of Figure 2 (left)

    10.17182/hepdata.85765.v1/t4

    Lower mass exclusion limits for scalar and vector LQs.

  • Figure 2b (2-d limit)

    Contents of Figure 2 (left)

    10.17182/hepdata.85765.v1/t5

    Observed upper limits on the production cross section for pair production of LQs decaying into a top quark and a...

  • Figure 2b (mass exclusion limits)

    Contents of Figure 2 (left)

    10.17182/hepdata.85765.v1/t6

    Lower mass exclusion limits for scalar and vector LQs.

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