Measurement of Inelastic J/Psi Photoproduction at HERA

The Zeus Collaboration

Paper

Measurement of Inelastic J/Psi Photoproduction at HERA

Abstract

We present a measurement of the inelastic, non diffractive J/

photoproduction cross section in the reaction

with the ZEUS detector at HERA. The J/

was identified using both the

and

decay channels and events were selected within the range

(

) for the muon (electron) decay mode, where

is the fraction of the photon energy carried by the J/

in the proton rest frame. The cross section, the

and the

distributions, after having subtracted the contributions from resolved photon and diffractive proton dissociative processes, are given for the photon-proton centre of mass energy range

GeV;

is the square of the J/

transverse momentum with respect to the incoming proton beam direction. In the kinematic range

and

GeV

, NLO calculations of the photon-gluon fusion process based on the colour-singlet model are in good agreement with the data. The predictions of a specific leading order colour-octet model, as formulated to describe the CDF data on J/

hadroproduction, are not consistent with the data.