Search for Pair Production of Second Generation Scalar Leptoquarks in ppbar Collisions at the Tevatron

As predicted by numerous extensions of the Standard Model, leptoquarks (LQ) are hypothetical bosons allowing lepton-quark transitions. Under the assumption that they couple only to quarks and leptons of the same generation, three generations of leptoquarks can be distinguished. The search for the pair production of second generation scalar leptoquarks has been carried out in pp collisions at √ s = 1.96TeV, using an integrated luminosity of 1 fb−1 collected by the DØ experiment at the Tevatron collider between August 2002 and February 2006. Topologies arising from the LQLQ → μqνq and LQLQ → μqμq decay modes have been investigated. In order to maximize the available statistics, a method for the combination of various prescaled triggers with an inclusive OR has been developed. Since no excess of data over the Standard Model prediction has been observed, upper limits on the leptoquark pair production cross section have been derived at 95% confidence level as function of the leptoquark mass and the branching fraction β = Br(LQ → μq), and are interpreted as lower limits on the leptoquark mass as function of β. For β = 1, β = 1/2 and β = 0.1, the combination of the two channels excludes scalar second generation leptoquarks with masses up to 309GeV, 262GeV, and 174GeV, respectively. The lower bounds on the scalar second generation leptoquark mass obtained for β ≥ 0.1 are the best exclusion limits to date.