Search for a third-generation leptoquark coupled to a $\tau$ lepton and a b quark through single, pair, and nonresonant production in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The CMS collaboration
Hayrapetyan, Aram , Tumasyan, Armen , Adam, Wolfgang , Andrejkovic, Janik Walter , Bergauer, Thomas , Chatterjee, Suman , Damanakis, Konstantinos , Dragicevic, Marko , Escalante Del Valle, Alberto , Hussain, Priya Sajid
JHEP 05 (2024) 311, 2024.

Abstract (data abstract)
A search is presented for a third-generation leptoquark (LQ) coupled exclusively to a $\tau$ lepton and a b quark. The search is based on proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13\,\mathrm{TeV}$ recorded with the CMS detector, corresponding to an integrated luminosity of $138\,\mathrm{fb}^{-1}$. Events with $\tau$ leptons and a varying number of jets originating from b quarks are considered, targeting the single and pair production of LQs, as well as nonresonant $t$-channel LQ exchange. An excess is observed in the data with respect to the background expectation in the combined analysis of all search regions. For a benchmark LQ mass of 2 TeV and a coupling strength of 2.5, the excess reaches local significances of up to 2.8 standard deviations. Upper limits at the $95\%$ confidence level are placed on the LQ production cross section in the LQ mass range 0.5-2.3 TeV, and up to 3 TeV for $t$-channel LQ exchange. Leptoquarks are excluded below masses of 1.22-1.88 TeV for different LQ models and varying coupling strengths up to 2.5. Considering only LQ exchange in the $t$ channel, constraints are placed on LQs with masses and coupling strengths of up to 3 TeV and 3.5, respectively.

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