Abstract
The most recent results from searches of leptoquark-like signatures are presented using 1.03 and 4.7 fb−1 of pp collision data collected by the ATLAS detector with s=7 TeV and 19.6 fb−1 of pp collision data collected by the CMS detector with s=8 TeV at the LHC. First- and second-generation scalar leptoquarks are looked for in the final states with either two leptons and two jets (ℓℓ+jj, ℓ=e, μ) or one lepton, missing transverse energy, and two jets (ℓν+jj, ℓ=e, μ). Apart from leptoquark investigations, the ℓℓ+jj final states are further studied in a search for W bosons with right-handed couplings that arise in left-right models. Third-generation scalar leptoquarks are looked for in the final state with two tau leptons and two b quarks or two top quarks (ττ+bb and ττ+tt). The ττ+bb final state is also sensitive to stop pairs decaying through R-parity violating and conserving processes that are foreseen in some models of supersymmetry. In addition, results are shown for third-generation scalar leptoquarks in the final states bb+νν and tt+νν, reinterpreting searches for bottom and top squark pair production. 95% confidence level upper limits are set on the scalar leptoquark pair production cross section times branching fraction in each decay channel as a function of the leptoquark mass and the branching ratio of decay.
Highlights
The “leptoquark” (LQ) are hypothetical particles that carry both lepton and baryon number. They are predicted in many extensions of the standard model (SM) of which grand unified theories (GUT) [1], composite models [2], extended technicolor models [3], and superstring-inspired models [4] are some examples
Specific properties are required: (a) leptoquarks need to have dimensionless couplings to SM lepton-quark pairs in order for their interactions to be renormalisable; (b) leptoquark interactions are required to be invariant under the Standard Model S U(3)C × S U(2)L × U(1)Y gauge groups; (c) leptoquark interactions with lepton-quark pairs are required to preserve baryon and lepton number separately, to avoid inducing rapid proton decay [6]; (d) leptoquarks couple to a single chirality and generation of SM fermions at a time, in order to suppress flavor-changing neutral currents (FCNCs) [7]
A complete description of the objects used in the analyses described below can be found in the corresponding references
Summary
The “leptoquark” (LQ) are hypothetical particles that carry both lepton and baryon number. They are SU(3) color-triplet bosons with different properties (spin, weak isospin, electric charge, chirality of the fermion couplings, and fermion number) depending on the structure of each specific model For this reason direct searches for leptoquarks at collider experiments are typically performed in the context of an effective leptoquark model: the Buchmuller-Ruckl-Wyler (BRW) model [5]. Single leptoquark production in association with a lepton proceeds through quark-gluon scattering and depends on the unknown Yukawa coupling λ These interactions are negligible due to the small relative value of λ suggested by stringent bounds from low-energy precision experiments for leptoquark masses MLQ < 1. A complete description of the objects used in the analyses described below can be found in the corresponding references
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