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Search for pair production of third-generation scalar leptoquarks decaying into a top quark and a $\tau$-lepton in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

The ATLAS collaboration
CERN-EP-2020-241, 2021.

Abstract (data abstract)
A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a $\tau$-lepton is presented. The search is based on a dataset of $pp$ collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$^{-1}$. Events are selected with one light lepton (electron or muon) and at least one hadronically decaying $\tau$-lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing $b$-hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The most sensitive event categories require at least one hadronically decaying $\tau$-lepton candidate and exploit the presence of energetic final state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, under different assumptions for the branching fractions into $t\tau$ and $b\nu$. Scalar leptoquarks decaying exclusively into $t\tau$ are excluded up to masses of $1.43$ TeV while, for a branching fraction of 50% into $t\tau$, the lower mass limit is $1.22$ TeV.

  • Acceptance times efficiency

    Table 06 of the auxiliary material.

    10.17182/hepdata.100174.v1/t1

    Selection efficiency times acceptance summed over the seven signal regions as a function of $m_{\mathrm{LQ}_{3}^{\mathrm{d}}}$, assuming B = 1.

  • Cross section upper limit at 95% CL

    Figure 15a.

    10.17182/hepdata.100174.v1/t2

    Summary of the observed and expected 95% CL upper limits on the cross section for $\mathrm{LQ}_{3}^{\mathrm{d}}$ pair production as a...

  • Branching fraction 95 %CL upper limit

    Figure 15b.

    10.17182/hepdata.100174.v1/t3

    Summary of the observed and expected 95% CL upper limits on B as a function of $m_{\mathrm{LQ}_{3}^{\mathrm{d}}}$.

  • Cutflow of pre-selection requirement

    Table 08 of the auxiliary material.

    10.17182/hepdata.100174.v1/t4

    Cutflow of the preselection requirements (see Section 5) for $\mathrm{LQ}_{3}^{\mathrm{d}}$ signals with $m_{\mathrm{LQ}_{3}^{\mathrm{d}}}$=0.9, 1.1, and 1.3 TeV, assuming B=1. The...

  • Cutflow of signal region requirements in 1L channels

    Table 09 of the auxiliary material.

    10.17182/hepdata.100174.v1/t5

    Cutflow of the signal region requirements in 1$\ell+\geq 1\tau$ channel (see Table 3) for $\mathrm{LQ}_{3}^{\mathrm{d}}$ signals with $m_{\mathrm{LQ}_{3}^{\mathrm{d}}}$=0.9, 1.1, and...

  • Cutflow of signal region requirements in 2L channels

    Table 10 of the auxiliary material.

    10.17182/hepdata.100174.v1/t6

    Cutflow of the signal region requirements in the 2$\ell$OS+$\geq 1\tau$ channel (see Table 4) for $\mathrm{LQ}_{3}^{\mathrm{d}}$ signals with $m_{\mathrm{LQ}_{3}^{\mathrm{d}}}$=0.9, 1.1,...

  • Cutflow of signal region requirements in ML channels

    Table 11 of the auxiliary material.

    10.17182/hepdata.100174.v1/t7

    Cutflow of the signal region requirements in the $2\ell$SS/$3\ell+\geq 1\tau$ channel (see Table 5) for $\mathrm{LQ}_{3}^{\mathrm{d}}$ signals with $m_{\mathrm{LQ}_{3}^{\mathrm{d}}}$=0.9, 1.1,...

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