Abstract
A search for new phenomena in final states with hadronically decaying tau leptons, $b$-jets, and missing transverse momentum is presented. The analyzed dataset comprises $pp$~collision data at a center-of-mass energy of $\sqrt s = 13$ TeV with an integrated luminosity of 139/fb, delivered by the Large Hadron Collider and recorded with the ATLAS detector from 2015 to 2018. The observed data are compatible with the expected Standard Model background. The results are interpreted in simplified models for two different scenarios. The first model is based on supersymmetry and considers pair production of top squarks, each of which decays into a $b$-quark, a neutrino and a tau slepton. Each tau slepton in turn decays into a tau lepton and a nearly massless gravitino. Within this model, top-squark masses up to 1.4 TeV can be excluded at the 95% confidence level over a wide range of tau-slepton masses. The second model considers pair production of leptoquarks with decays into third-generation leptons and quarks. Depending on the branching fraction into charged leptons, leptoquarks with masses up to around 1.25 TeV can be excluded at the 95% confidence level for the case of scalar leptoquarks and up to 1.8 TeV (1.5 TeV) for vector leptoquarks in a Yang--Mills (minimal-coupling) scenario. In addition, model-independent upper limits are set on the cross section of processes beyond the Standard Model.
Highlights
The Standard Model (SM) of particle physics has been verified to high precision
As the sensitivity of the search is dominated by the category where both tau leptons decay hadronically, this paper considers only events with hadronically decaying tau leptons
The second benchmark model used in the design of the analysis considers pair production of scalar leptoquarks
Summary
The Standard Model (SM) of particle physics has been verified to high precision. Despite its success, several observations have been made which have exposed the theory’s shortcomings in various aspects and fostered new theoretical ideas. For a branching fraction BðLQu3=d → qlÞ ∼ 0.5, most of the decays of the pair of third-generation leptoquarks yield a final state with one tau lepton, two b-jets and large EmT iss from the tau neutrino. The CMS Collaboration has published a search of the full run-2 dataset for single or pair production of scalar or vector leptoquarks coupling to thirdgeneration fermions, considering final-state signatures consisting of a top quark, a tau lepton, a neutrino, and either no or at least one additional b-tagged jet. This search excludes scalar leptoquarks with masses up to about. Models with vector leptoquarks have been considered in several analyses by the CMS Collaboration, including the one in Ref. [64], which excludes vector leptoquarks decaying into tντ=bτþ with masses up to 1.65 TeV for pair production in the most favorable coupling scenario
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