Search for pairs of scalar leptoquarks decaying into quarks and electrons or muons in s $$ \sqrt{s} $$ = 13 TeV pp col
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Received: June 11, 2020 Accepted: September 7, 2020 Published: October 16, 2020
The ATLAS collaboration E-mail: [email protected] Abstract: A search for new-physics resonances decaying into a lepton and a jet performed by the ATLAS experiment is presented. Scalar leptoquarks pair-produced in pp collisions √ at s = 13 TeV at the Large Hadron Collider are considered using an integrated luminosity of 139 fb−1 , corresponding to the full Run 2 dataset. They are searched for in events with two electrons or two muons and two or more jets, including jets identified as arising from the fragmentation of c- or b-quarks. The observed yield in each channel is consistent with the Standard Model background expectation. Leptoquarks with masses below 1.8 TeV and 1.7 TeV are excluded in the electron and muon channels, respectively, assuming a branching ratio into a charged lepton and a quark of 100%, with minimal dependence on the quark flavour. Upper limits on the aforementioned branching ratio are also given as a function of the leptoquark mass. Keywords: Beyond Standard Model, Exotics, Hadron-Hadron scattering (experiments), Particle and resonance production ArXiv ePrint: 2006.05872
Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP3 .
https://doi.org/10.1007/JHEP10(2020)112
JHEP10(2020)112
Search for pairs of scalar leptoquarks decaying into √ quarks and electrons or muons in s = 13 TeV pp collisions with the ATLAS detector
Contents 1
2 The ATLAS detector
3
3 Data and Monte Carlo samples
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4 Event reconstruction and object definitions
5
5 Event selection
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6 Background determination
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7 Systematic uncertainties
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8 Results
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9 Conclusion
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The ATLAS collaboration
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1
Introduction
Leptoquarks (LQs) are hypothetical colour-triplet particles that carry both baryon and lepton quantum numbers (B 6= 0, L 6= 0). As such, LQs couple simultaneously to both quarks and leptons, enabling direct transitions between the two. The spin of a LQ state is either 0 (scalar LQ) or 1 (vector LQ), and only the former is considered in this paper. Because of their SU(3) and SU(2) charge (colour and weak isospin, respectively), LQs can mediate flavour-changing neutral currents, and enable the violation of lepton flavour universality, which has been suggested as an explanation of recent measurements of B-meson decays [1–7]. New-physics models involving LQs might also resolve several interesting physical phenomena observed in nature. For instance, LQs can be used to explain the origins of the neutrino masses [8–11], as well as the origins of CP violation, thereby explaining the observed matter/antimatter asymmetry in the universe [12, 13]. In addition, LQs could provide a satisfying connection between the apparent symmetry of lepton and quark generations, as well as unification of the electromagnetic and weak forces at high energy [14, 15]. At the LHC, the pair production of LQs is possible via gluon-gluon fusion and quarkantiquark annihilation, as shown in fi
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