Observation of electrons produced in association with hard jets and large missing transverse momentum in pp collisions at s = 540 GeV

Using a sample of events collected by UA2 and corresponding to an integrated luminosity of 116 nb−1. we have searched for electron-“neutrino” pairs in which the transverse momenta of the electron and of the “neutrino” exceed 15 GeV/c and 25 GeV/c respectively. A total of 35 events are observed in low background conditions. Most events can be interpreted in terms of W± production from QCD processes. Events in which the observation of hard jets makes this interpretation unlikely are described in detail. Possible sources of background contamination are considered.