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

Abstract

A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton is presented. The search is based on a dataset of pp collisions at $$ \sqrt{s} $$ 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 if they have one light lepton (electron or muon) and at least one hadronically decaying τ -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 signal-rich event categories require at least one hadronically decaying τ-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, for different assumptions about the branching fractions into tτ and bν. Scalar leptoquarks decaying exclusively into tτ are excluded up to masses of 1.43 TeV while, for a branching fraction of 50% into tτ, the lower mass limit is 1.22 TeV.

Explaining lepton-flavor non-universality and self-interacting dark matter with $L_μ-L_τ$

“…The vertical blue band corresponds to the Z → τ τ constraint. The gray and purple band represent exclusions from LQ pair production in pp → t tτ τ [86] and from the most recent LHC searches in the high-pT bins of pp → τ τ at √ s = 13 TeV with 140 fb −1 [67,68], respectively. The red curved band corresponds to the exclusion from Bc → τ ντ decay with the conservative limit on branching ratio < 30% [81].…”

“…Thus, collider bounds from single-LQ production are less significant compared to QCD-driven LQ pair production. S 1 pairs primarily decay to b bνν [90] and t tτ τ [86] (branching ratio β ≤ 0.5) via the coupling z L b , and to jjτ τ through the coupling z R c . There are no dedicated searches for jjτ τ decays and the limit from b bνν is m S1 > 1.0 TeV for β = 1.…”

“…FIG.2: 1σ (green) and 2σ (yellow) allowed range for R D ( * ) in the relevant Yukawa coupling plane, with the S1 LQ mass fixed at 1.0 TeV for the case withC τ s = −4C τ T ∈ i (top) and C τ s = −4C τ T ∈ (bottom).The vertical blue band corresponds to the Z → τ τ constraint. The gray and purple band represent exclusions from LQ pair production in pp → t tτ τ[86] and from the most recent LHC searches in the high-pT bins of pp → τ τ at √ s = 13 TeV with 140 fb −1[67,68], re-…”

Searches for leptoquarks in scenarios of lepton flavor universality anomalies

“…Leptoquarks decaying to t or b have been sought for systematically by the ATLAS and CMS Collaborations. In searches that target exclusive decays to t (B = 1) using 139 and 35.9 fb −1 of data, ATLAS [19] and CMS [20] exclude pair-produced scalar LQs below masses of 0.9 and about 1.4 TeV, respectively. The case of B = 0.5 has been studied by both ATLAS and CMS using datasets of 139 and 137 fb −1 , respectively.…”

Searches for leptoquarks in scenarios of lepton flavor universality anomalies

“…Leptoquarks decaying to t𝜏 or b𝜈 have been sought for systematically by the ATLAS and CMS Collaborations. In searches that target exclusive decays to t𝜏 (B = 1) using 139 and 35.9 fb −1 of data, ATLAS [19] and CMS [20] exclude pair-produced scalar LQs below masses of 0.9 and about 1.4 TeV, respectively. The case of B = 0.5 has been studied by both ATLAS and CMS using datasets of 139 and 137 fb −1 , respectively.…”