Rare phenomenon and W production in electron-proton scattering at HERA

Abstract

A general and model-independent search for deviations from the standard model prediction is performed in ep collisions at HERA using H1 data corresponding to an integrated luminosity of 115 pb"-"1. All experimentally measurable event topologies involving electrons, photons, muons, neutrinos and jets with high transverse momenta are investigated. Events are classified into exclusive event classes according to their final state. A new algorithm is used to look for regions with deviations from the standard model in the invariant mass and sum of transverse momenta distributions and to quantify the significance of the observed deviations. A good agreement with the standard model prediction is found in most of the event classes. The largest deviation occurs in topologies with an isolated muon, missing transverse momentum and a jet. About 2% of hypothetical Monte Carlo experiments would produce deviations more significant than the one observed in the corresponding sum of transverse momenta distribution. Within the standard model events with an isolated muon, or, more general, a charged lepton, and missing transverse momentum are expected to be mainly due to W boson production with subsequent leptonic decay. The H1 and ZEUS collaborations have already searched for such events and found, in accordance with the general search, an excess of events with high transverse momentum of the hadronic system. Complementary, a search for W bosons in the dominant hadronic decay channel is performed. The phase space is optimised to maximise the acceptance for W events and reduce other standard model contributions. The data are compared to the predictions of quantum chromodynamics as a function of the transverse momentum of the hadronic system after excluding the W candidate jets and found to be in good agreement in this regard. (orig.)Available from TIB Hannover: RA 8919(2004-048) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman