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.