We describe a search for the pair production of first-generation scalar and
vector leptoquarks in the eejj and evjj channels by the DO Collaboration.
The data are from the 1992-1996 p (p) over bar run at roots = 1.8 TeV at th
e Fermilab Tevatron collider. We find no evidence for leptoquark production
: in addition. no kinematically interesting events are observed using relax
ed selection criteria. The results from the eejj and evjj channels are comb
ined with those from a previous DO analysis of the vvjj channel to obtain 9
5% confidence level (C.L.) upper limits on the leptoquark pair-production c
ross section as a function of mass and of beta. the branching fraction to a
charged lepton. These limits are compared to next-to-leading-order theory
to set 95% C.L. lower limits on the mass of a first-generation scalar lepto
quark of 225, 204, and 79 GeV/c(2) for beta = 1. 1/2. and 0, respectively.
For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower li
mits of 345. 337, and 206 GeV/c(2) are set on the mass for beta = 1, 1/2, a
nd 0. respectively. Mass limits for vector leptoquarks are also set for ano
malous vector couplings.