Elastic Z^0 production at HERA

Abstract

The production of $Z^{0}$ bosons in the reaction $eparrow eZ^{0}p^{(*)}$, where $p^{(*)}$ stands for a proton or a low-mass nucleon resonance, has been studied in $ep$ collisions at HERA using the ZEUS detector. The analysis is based on a data sample collected between 1996 and 2007, amounting to 496\, pb$^{-1}$ of integrated luminosity. The $Z^{0}$ was measured in the hadronic decay mode. The elasticity of the events was ensured by a cut on $\eta_{{\rm max}} < 3.0$, where $\eta_{{\rm max}}$ is the maximum pseudorapidity of 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 $ep arrow eZ^{0}p^{(*)}$ was measured to be $\sigma (ep arrow eZ^{0}p^{(*)}) = {\rm 0.13 \pm{0.06} ({\rm stat.}) \pm{0.01} ({\rm syst.})}\, {\rm pb}$, in agreement with the Standard Model prediction of $0.16\, {\rm pb}$. This is the first measurement of $Z^{0}$ production in $ep$ collisions. In this paper we report the already published ZEUS result by adding the sensitivities of the most recent similar results from CMS and ATLAS.