Search for an excited lepton that decays via a contact interaction to a lepton and two jets in proton-proton collisions
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Springer
Received: January Revised: March Accepted: April Published: May
13, 31, 18, 12,
2020 2020 2020 2020
The CMS collaboration E-mail: [email protected] Abstract: Results are presented from a search for events containing an excited lepton (electron or muon) produced in association with an ordinary lepton of the same flavor and decaying to a lepton and two hadronic jets. Both the production and the decay of the excited leptons are assumed to occur via a contact interaction with a characteristic energy scale Λ. The branching fraction for the decay mode under study increases with the mass of the excited lepton and is the most sensitive channel for very heavy excited leptons. The analysis uses a sample of proton-proton collisions collected by the CMS experiment √ at the LHC at s = 13 TeV, corresponding to an integrated luminosity of 77.4 fb−1 . The four-body invariant mass of the two lepton plus two jet system is used as the primary discriminating variable. No significant excess of events beyond the expectation for standard model processes is observed. Assuming that Λ is equal to the mass of the excited leptons, excited electrons and muons with masses below 5.6 and 5.7 TeV, respectively, are excluded at 95% confidence level. These are the best limits to date. Keywords: Beyond Standard Model, Hadron-Hadron scattering (experiments) ArXiv ePrint: 2001.04521
Open Access, Copyright CERN, for the benefit of the CMS Collaboration. 3 Article funded by SCOAP .
https://doi.org/10.1007/JHEP05(2020)052
JHEP05(2020)052
Search for an excited lepton that decays via a contact interaction to a lepton and two jets in proton-proton √ collisions at s = 13 TeV
Contents 1
2 The CMS detector
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3 Model and signal simulation
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4 Event reconstruction
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5 Backgrounds
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6 Event selection and validation regions
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7 Systematic uncertainties
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8 Results
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9 Summary
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The CMS collaboration
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1
Introduction
The standard model (SM) of particle physics accurately describes a broad range of observations, but it does not provide an explanation for many of its own features. Among the most prominent of these features is the existence of three fermion generations, encompassing both leptons and quarks. Attempts to explain the observed generation structure have led to a class of models postulating that quarks and leptons are composite objects that consist of more fundamental constituents [1–9]. In these models, the fundamental constituents are bound by an asymptotically free gauge interaction that becomes strong below a characteristic scale Λ. Such compositeness models predict the existence of excited states of quarks (q ∗ ) and leptons (`∗ ) at the characteristic scale of the new binding interaction. Since these excited fermions couple to ordinary SM fermions, they could be produced via contact interactions (CI) in collider experiments, with subsequent decays to SM fermions through the gauge interactions (GIs), via the emission of a W or Z boson or a photon (γ), or via a CI to other fermions. Search
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