Search for Second-Generation Leptoquarks in Proton-Antiproton Collisions

This document describes the search for second-generation
leptoquarks (LQ_2) in around 114 pb^-1 of proton-antiproton
collisions, recorded with the D0 detector between September 2002
and June 2003 at a centre-of-mass energy of sqrt{s} = 1.96 TeV. The
predictions of the Standard Model and models including scalar
leptoquark production are compared to the data for various
kinematic distributions. Since no excess of data over the Standard
Model prediction has been observed, a lower limit on the leptoquark
mass of M(LQ_2)_{beta=1} > 200 GeV/c^2 has been calculated at
95% confidence level (C.L.), assuming a branching fraction of beta
= BF(LQ_2 --> mu j) = 100% into a charged lepton and a quark.
The corresponding limit for beta = 1/2 is M(LQ_2)_{beta=1/2} >
152 GeV/c^2. Finally, the results were combined with those from the
search in the same channel at D0 Run I. This combination yields the
exclusion limit of 222 GeV/c^2 (177 GeV/c^2) for beta=1 (1/2) at
95% C.L., which is the best exclusion limit for scalar
second-generation leptoquarks (for beta=1) from a single experiment
to date.