Searches for scalar leptoquarks and differential cross-section measurements in dilepton–dijet events in proton–proton collisions at a centre-of-mass energy of $$\varvec{\sqrt{s}}$$ = 13 TeV with the ATLAS experiment

Abstract

The ATLAS CollaborationSearches for scalar leptoquarks pair-produced in proton-proton collisions at √ 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 Z → ee, Z → µµ and tt 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 Z → measurements in observables sensitive to jet energies disagree with the data.Electrons are reconstructed from ID tracks which are matched to energy clusters found in the electromagnetic calorimeter. The reconstruction efficiency is higher than 97% for candidates with p T greater than 30 GeV. An object is identified as an electron following requirements made on the quality of the associated track, shower shapes exploiting the longitudinal segmentation of the electromagnetic calorimeter, leakage into the hadronic calorimeter, the quality of the track-to-cluster matching and measurements of transition radiation made with the TRT [71]. The transverse energy of the electron candidates in the ee j j (eν j j) channel must exceed 40 (65) GeV. Only electron candidates in the pseudorapidity region |η| < 2.47 and excluding

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“…CMS has * kushagra.chandak@research.iiit.ac.in † tanumoy.mandal@physics.uu.se ‡ subhadip.mitra@iiit.ac.in also put bounds on scalar LQs that decay to a b-quark and a neutrino at about 1.1 TeV assuming 100% BR in this decay mode [35]. Similar limits are also available from the ATLAS searches [36,37].…”

Non-standard interactions in radiative neutrino mass models

“…There are dedicated searches for pair production of first [180,181], second [181][182][183] and third generation [183][184][185] LQs at the LHC. Given the model Lagrangian 5.1, we are interested in the final states containing either two charged leptons and two jets ( jj), or two neutrinos and two jets (ννjj).…”

Robust Independent Validation of Experiment and Theory: Rivet version 3

“…the studies of simplified BSM models that LHC experiments use ubiquitously as phenomenological demonstrations of analysis impact, it has typically been neglected from search analyses. While this culture is necessarily changing in the high-statistics limit of LHC running, where an extra 6 months of data-taking does not automatically revolutionise the previous measurements, and in the realisation that simplified models are not always good proxies for full UV-complete BSM models [44,84], it remains the case that with a few exceptions [85,86], unfolding is currently rarely part of the vocabulary of collider BSM direct-search analyses.…”