Köln 2004 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 11: Poster Session: Electromagnetic and Hadronic Probes

HK 11.2: Poster

Tuesday, March 9, 2004, 13:30–15:30, Foyer

Charmonium photoproduction. — •Alexander Sibirtsev¹, Siegfried Krewald¹, and Anthony W. Thomas² — ¹IKP-TH, FZJ, Juelich. — ²Adelaide University

The available data on J/Ψ photoproduction are analyzed in terms of pomeron exchange, two gluon exchange and photon-gluon fusion models. Allowing the pomeron-quark interaction to be flavour dependent and introducing the soft and hard pomerons it is possible to reproduce the data at √s>10 GeV and small |t|. The two gluon exchange calculations indicate strong sensitivity to the gluon distribution function. The results obtained with the most modern MRST2001 and DL PDF reproduce the forward J/Ψ photoproduction cross section at √s>10 GeV. The calculations with the photon-gluon fusion model and with MRST2001 and DL PDF are also in reasonable agreement with the data on the total J/Ψ photoproduction cross section. However none of the models describe the data at √s<10 GeV or |t|≥1 GeV². We attribute the J/Ψ photoproduction at low energies and large |t| to a mechanism different from pomeron or two gluon exchange. We consider that this might be the exchange of an axial vector trajectory that couples to the axial form factor of the nucleon.