Studies of the diffractive photoproduction of isolated photons at HERA

Abramowicz, H.; Abt, I.; Adamczyk, L.; Adamus, M.; Antonelli, S.; Aushev, V.; Aushev, Y.; Behnke, O.; Behrens, U.; Bertolin, A.; Bloch, I.; Brock, I.; Brook, N.  H.; Brugnera, R.; Bruni, A.; Bussey, P.  J.; Caldwell, A.; Capua, M.; Catterall, C.  D.; Chwastowski, J.; Ciborowski, J.; Ciesielski, R.; Cooper-Sarkar, A.  M.; Corradi, M.; Dementiev, R.  K.; Devenish, R.  C.  E.; Dusini, S.; Foster, B.; Gach, G.; Gallo, E.; Garfagnini, A.; Geiser, A.; Gizhko, A.; Gladilin, L.  K.; Golubkov, Yu.  A.; Grzelak, G.; Guzik, M.; Gwenlan, C.; Hlushchenko, O.; Hochman, D.; Hori, R.; Ibrahim, Z.  A.; Iga, Y.; Ishitsuka, M.; Jomhari, N.  Z.; Kadenko, I.; Kananov, S.; Karshon, U.; Kaur, P.; Kisielewska, D.; Klanner, R.; Klein, U.; Korzhavina, I.  A.; Kotański, A.; Kovalchuk, N.; Kowalski, H.; Krupa, B.; Kuprash, O.; Kuze, M.; Levchenko, B.  B.; Levy, A.; Lisovyi, M.; Lobodzinska, E.; Löhr, B.; Lohrmann, E.; Longhin, A.; Lukina, O.  Yu.; Malka, J.; Mastroberardino, A.; Mohamad Idris, F.; Mohammad Nasir, N.; Myronenko, V.; Nagano, K.; Onishchuk, Yu.; Paul, E.; Perlański, W.; Pokrovskiy, N.  S.; Polini, A.; Przybycień, M.; Ruspa, M.; Saxon, D.  H.; Schioppa, M.; Schneekloth, U.; Schörner-Sadenius, T.; Shcheglova, L.  M.; Shkola, O.; Shyrma, Yu.; Skillicorn, I.  O.; Słomiński, W.; Solano, A.; Stanco, L.; Stefaniuk, N.; Stern, A.; Stopa, P.; Sztuk-Dambietz, J.; Tassi, E.; Tokushuku, K.; Tomaszewska, J.; Tsurugai, T.; Turcato, M.; Turkot, O.; Tymieniecka, T.; Verbytskyi, A.; Wan Abdullah, W.  A.  T.; Wichmann, K.; Wing, M.; Yamada, S.; Yamazaki, Y.; Żarnecki, A.  F.; Zawiejski, L.; Zenaiev, O.; Zhautykov, B.  O.

doi:10.1103/physrevd.96.032006

The photoproduction of isolated photons has been measured in diffractive events recorded by the ZEUS detector at HERA. Cross sections are evaluated in the photon transverse- energy and pseudorapidity ranges 5 < E_T(gamma) < 15 GeV and -0.7 < eta(gamma) < 0.9, inclusively, and also with a jet with transverse energy and pseudorapidity in the ranges 4 < E_T(jet) < 35 GeV and -1.5 < 1.8, using a total integrated electron-proton luminosity of 456 pb-1. A number of kinematic variables were studied and compared to predictions from the RAPGAP Monte Carlo model. An excess of data is observed above the RAPGAP predictions for z(P)(meas) > 0.9, where z(P)(meas) is the fraction of the longitudinal momentum of the colorless "Pomeron" exchange that is transferred to the photon- jet final state, giving evidence for direct Pomeron interactions.