Leptoquark Mass Limits from Single Leptoquark Production at LEP and LEP200

Abstract

We investigate the discovery potential for first generation leptoquarks at the LEP and LEP200 $e^+e^-$ colliders. We consider single leptoquark production via resolved photon contributions which offers a much higher kinematic limit than the more commonly considered leptoquark pair production process. This process also has the advantage that it is independent of the leptoquark chirality, is almost insensitive to whether the leptoquark is scalar or vector, and only depends on the leptoquark charge. We estimate that from the nonobservation of energetic $e-jet$ events, the limits at LEP for all types of leptoquarks are $M_{LQ} > 90$~GeV. For the just completed $\sqrt{s}=161$~GeV run at LEP200 we estimate potential scalar leptoquark mass limits of $M_{LQ} > 130$~GeV for $Q_{LQ}=-2/3, \; -4/3$ and $M_{LQ} > 148$~GeV for $Q_{LQ}=-1/3, \; -5/3$ and for vector LQ's the limits are 140 and 154~GeV respectively. Ultimately, LEP200 should be able to achieve discovery limits for leptoquarks of $\sim 188$~GeV for the $\sqrt{s}=190$~GeV runs. In all cases we assume electromagnetic strength coupling.