W production and the search for events with an isolated high-energy lepton and missing transverse momentum at HERA

A search for the leptonic decays of W bosons produced in the reaction e+p→e+W±X at a centre-of-mass energy of 300 GeV has been performed with the ZEUS detector at HERA using an integrated luminosity of 47.7 pb−1. Three events consistent with W→eν decay are found, giving a cross section estimate of 0.9+1.0−0.7±0.2 pb, in good agreement with the Standard Model prediction. The corresponding 95% C.L. upper limit on the cross section is 3.3 pb. A search for the decay W→μν has a smaller selection efficiency and yields no candidate events. Limits on the cross section for W production with large hadronic transverse momentum have been obtained. A search for high-transverse-momentum isolated tracks in events with large missing transverse momentum yields results in good agreement with Standard Model expectations, in contrast to a recent report by the H1 collaboration of the observation of an excess of such events.