Exclusive production of J/#psi# mesons in the ZEUS detector

Exclusive J/#psi# production has been studied using the ZEUS detector at HERA. Two ranges of the photon virtuality, Q"2<1 GeV"2 and 0.15<Q"2<0.8 GeV"2 are examined. The latter is defined by requiring the scattered electron to be detected in the Beam Pipe Calorimeter under low angles. The J/#psi# mesons have been identified via the decay J/#psi##->#e"+e"-. The cross sections are measured as a function of the photon-proton centre-of-mass energy, W. The data used were taken during the 1999 and 2000 running periods, which yielded an integrated luminosity of 68.7 pb"-"1. The measured W dependences are in agreement with each other and the values obtained in high-Q"2 (2<Q"2<100 GeV"2) measurements. This leads to the conclusion that J/#psi# production is a hard process for all Q"2 values and can be described with models based on perturbative QCD. Electron-pion separation of the ZEUS Transition Radiation Detector is measured. A method to combine TRD information and dE/dx measurements from the central drift chamber is developed and applied to the Q"2<1GeV"2 J/#psi# sample. (orig.)SIGLEAvailable from TIB Hannover: RN 4852(2003-06) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman