Abstract

Searches for scalar leptoquarks pair-produced in proton–proton collisions at sqrt{s}=13 TeV at the Large Hadron Collider are performed by the ATLAS experiment. A data set corresponding to an integrated luminosity of 36.1 fb^{-1} is used. Final states containing two electrons or two muons and two or more jets are studied, as are states with one electron or muon, missing transverse momentum and two or more jets. No statistically significant excess above the Standard Model expectation is observed. The observed and expected lower limits on the leptoquark mass at 95% confidence level extend up to 1.29 TeV and 1.23 TeV for first- and second-generation leptoquarks, respectively, as postulated in the minimal Buchmüller–Rückl–Wyler model, assuming a branching ratio into a charged lepton and a quark of 50%. In addition, measurements of particle-level fiducial and differential cross sections are presented for the Zrightarrow ee, Zrightarrow mu mu and tbar{t} processes in several regions related to the search control regions. Predictions from a range of generators are compared with the measurements, and good agreement is seen for many of the observables. However, the predictions for the Zrightarrow ell ell measurements in observables sensitive to jet energies disagree with the data.

Highlights

  • Leptoquarks (LQs) are features of a number of extensions of the Standard Model (SM) [1,2,3,4,5,6,7,8] and may provide an explanation for the similarities between the quark and lepton sectors in the SM

  • The results presented here significantly extend the sensitivity in mass compared to previous ATLAS results, and yield an exclusion very similar to that found by the CMS experiment using a dataset of a similar size [27,28]

  • Two measurement regions are identical to the Z control regions used in the search, and their fiducial cross-

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Summary

Introduction

Leptoquarks (LQs) are features of a number of extensions of the Standard Model (SM) [1,2,3,4,5,6,7,8] and may provide an explanation for the similarities between the quark and lepton sectors in the SM. They appear in models addressing some of the recent b-flavour anomalies [9,10,11]. The results obtained here can, be regarded as conservative estimates of limits on vector LQ production, since the production cross-section for vector LQs is typically much larger than for scalar LQs, while the kinematic properties used to search for their signature are very similar for both spin hypotheses [8]

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