Search for resonances decaying to e(+)-jet in e(+)p interactions at HERA

The e(+)-jet invariant mass spectrum produced in the reaction e(+)p --> e(+)X has been studied at a center-of-mass energy of 300 GeV. The data were collected. using the ZEUS detector operating at the HERA collider, and correspond to an integrated luminosity of 47.7 pb(-1). The observed mass spectrum is in good agreement with Standard Model expectations up to an e(+)-jet mass of 210 GeV. Above this mass. some excess is seen. The angular distribution of these events is typical of high-Q(2) neutral current events and does not give convincing evidence for the presence of a narrow scalar or vector state. Limits are presented on the product of cross section and branching ratio for such a slate and are interpreted as limits on leptoquark or R-parity-violating squark production. Specific leptoquark types are ruled out at 95% confidence level for coupling strength lambda = 0.3 for masses between 150 and 280 GeV.