Abstract
A search for pair production of scalar leptoquarks, each decaying into either an electron or a muon and a top quark, is presented. This is the first leptoquark search using ATLAS data to investigate top-philic cross-generational couplings that could provide explanations for recently observed anomalies in B meson decays. This analysis targets high leptoquark masses which cause the decay products of each resultant top quark to be contained within a single high-p_{mathrm {T}} large-radius jet. The full Run 2 dataset is exploited, consisting of 139~hbox {fb}^{-1} of data collected from proton–proton collisions at sqrt{s}=13~mathrm {TeV} from 2015 to 2018 with the ATLAS detector at the CERN Large Hadron Collider. In the absence of any significant deviation from the background expectation, lower limits on the leptoquark masses are set at 1480~mathrm {GeV} and 1470~mathrm {GeV} for the electron and muon channel, respectively.
Highlights
The quark and lepton sectors of the standard model (SM) are interestingly similar, motivating one to hypothesize a fundamental symmetry between the two sectors
For the LQ signal, in addition to the cross-section uncertainties, the impact on the acceptance due to variations of the quantum chromodynamics (QCD) scales, parton distribution function (PDF) and shower parameters was studied. These uncertainties were estimated from the envelope of independent pairs of renormalization and factorization scale variations by a factor of 0.5 and 2, by propagating the PDF and αS uncertainties following the PDF4LHC15 prescription, and by considering two alternative samples generated with settings that increase or decrease the amount of QCD radiation
This function depends on the signal strength parameter μ, a multiplicative factor applied to the theoretical signal production cross section, and θ, a set of nuisance parameters that encode the effect of systematic uncertainties in the signal and background expectations and are implemented in the likelihood function as Gaussian and log-normal constraints
Summary
The quark and lepton sectors of the standard model (SM) are interestingly similar, motivating one to hypothesize a fundamental symmetry between the two sectors Such a symmetry can be found in many grand unified theories, such as grand unified SU(5) [1], the Pati–Salam model based on SU(4) [2], or R-parity-violating (RPV) supersymmetry (SUSY) models [3]. LQs are hypothetical colour-triplet bosons which couple directly to quarks and leptons They can be of either scalar or vector nature, and carry fractional electric charge. At the Large Hadron Collider (LHC) [14], LQs could be produced in pairs, or singly in association with a lepton This analysis targets LQ pair production, which is dominated by strong interactions and largely insensitive to the Yukawa coupling at a LQ–lepton–quark vertex. The CMS Collaboration has published a search using 35.9 fb−1 of data collected in 2015–2016 that excluded masses below 1420 GeV for scalar LQs decaying exclusively into tμ [22]
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