Production of Z(0) bosons in elastic and quasi-elastic ep collisions at HERA

The production of Z 0 bosons in the reaction ep→eZ 0 p (*) , where p (*) stands for a proton or a low-mass nucleon resonance, has been studied in ep collisions at HERAusing the ZEUS detector. The analysis is based on a data sample collected between 1996 and 2007, amounting to 496pb -1 of integrated luminosity. The Z 0 was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on η max max is the maximum pseudorapidityof energy deposits in the calorimeter defined with respect to the proton beam direction. A signal was observed at the Z 0 mass. The cross section of the reaction ep→eZ 0 p (*) was measured to be σ(ep→eZ 0 p (*) )=0.13±0.06(stat.)±0.01(syst.) pb, in agreement with the Standard Model prediction of 0.16 pb. This is the first measurement of Z 0 production in ep collisions. © 2012 Elsevier B.V.