Search for first-generation scalar and vector leptoquarks

We describe a search for the pair production of first-generation scalar and vector leptoquarks in the $\mathrm{eejj}$ and $e\nu \mathrm{jj}$ channels by the DØ Collaboration. The data are from the 1992–1996 $p\overline{p}$ run at $\sqrt{s}=1.8\mathrm{}\hspace{0.5em}\mathrm{TeV}$ at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the $\mathrm{eejj}$ and $e\nu \mathrm{jj}$ channels are combined with those from a previous DØ analysis of the $\nu \nu \mathrm{jj}$ channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross 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 leptoquark of 225, 204, and 79 $\mathrm{GeV}{/c}^2$ for $\beta =1,$ $\frac{1}{2},$ and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345, 337, and 206 $\mathrm{GeV}{/c}^2$ are set on the mass for $\beta =1,$ $\frac{1}{2},$ and 0, respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings.