Abstract
This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35/pb of proton-proton collision data recorded by the ATLAS detector at sqrt(s)=7 TeV. Leptoquarks are seached in events with two oppositely charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses mLQ<376 (319) GeV and mLQ<422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).
Highlights
The standard model is extremely successful at describing the elementary particles and their interactions, yet it gives no explanation for the striking symmetry between quarks (q) and leptons (‘)
The data are indicated by the points and the standard model backgrounds are shown with cumulative distributions
Data and standard model expectations are in good agreement. 95% CL upper limits on LQ pairproduction cross sections are determined using a modified
Summary
The standard model is extremely successful at describing the elementary particles and their interactions, yet it gives no explanation for the striking symmetry between quarks (q) and leptons (‘). This has, in part, been the motivation for many beyond-the-standard-model theories that posit the existence of leptoquarks (LQ), particles that carry both lepton and baryon quantum numbers, which couple to both quarks and leptons, and carry the triplet charge of quantum chromodynamics (QCD), color. Direct leptoquark searches at electron–proton colliders have sensitivity to first generation leptoquarks, but have a non-negligible dependence on the value of the LQ À ‘ À q coupling [6], whereas second and third generation leptoquarks are produced via lepton-flavor-violation mechanisms [7]. The cross sections for the leptoquark-mediated processes pp ! lljj and ljj can be written as LQ Â 2 and LQ Â 2 ð1 À Þ, respectively, where is the branching fraction for a single leptoquark to decay into a charged lepton and a quark
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