Color-octet contributions to J/#psi# photoproduction via fragmentation at HERA

We study J/#psi# photoproduction via fragmentation at next-to-leading order in the QCD-improved parton model, using the nonrelativistic factorization formalism proposed by Bodwin, Braaten, and Lepage. We consider direct and resolved photoproduction of prompt J/#psi# mesons and #chi#_c_J mesons radiatively decaying to J/#psi#+#gamma#, taking into account the formation of both color-singlet and color-octet cc states. Adopting the values of the long-distance color-octet matrix elements extracted from fits to prompt-J/#psi# data recently taken at the Fermilab Tevatron, we predict that measurements of J/#psi# photoproduction at DESY HERA should show a distinctive excess over the expectation based on the color-singlet model at small values of the inelasticity variable z. This is complementary to the expected enhancement at z<or#approx#1 due to the color-octet contribution to photon-gluon fusion. (orig.)Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman