Exclusive leptoproduction of real photons on a longitudinally polarised hydrogen target

Airapetian, A.; Akopov, N.; Akopov, Z.; Aschenauer, E. C.; Augustyniak, W.; Avakian, R.; Avetissian, A.; Avetisyan, E.; Ball, B.; Belostotski, S.; Bianchi, N.; Blok, H. P.; Bottcher, H.; Borissov, A.; Bowles, J.; Brodski, I.; Bryzgalov, V.; Burns, J.; Capiluppi, Marco; Capitani, G. P.; Cisbani, E.; Ciullo, Giuseppe; Contalbrigo, Marco; Ferretti, Paola; Deconinck, W.; Leo, R. D.; Nardo, L. D.; Sanctis, E. D.; Diefenthaler, M.; Nezza, P. D.; Duren, M.; Ehrenfried, M.; Elbakian, G.; Ellinghaus, F.; Fabbri, R.; Fantoni, A.; Felawka, L.; Frullani, S.; Gabbert, D.; Gapienko, G.; Gapienko, V.; Garibaldi, F.; Gavrilov, G.; Gharibyan, V.; Giordano, Francesca; Gliske, S.; Golembiovskaya, M.; Hadjidakis, C.; Hartig, M.; Hasch, D.; Hill, G.; Hillenbrand, A.; Hoek, M.; Holler, Y.; Hristova, I.; Imazu, Y.; Ivanilov, A.; Izotov, A.; Jackson, H.; H. S., Jo; Joosten, S.; Kaiser, R.; Karyan, G.; Keri, T.; Kinney, E.; Kisselev, A.; Kobayashi, N.; Korotkov, V.; Kozlov, V.; Kravchenko, P.; Krivokhijine, V. G.; Lagamba, L.; Lamb, R.; Lapikas, L.; Lehmann, I.; Lenisa, Paolo; Linden Levy, L. A.; Ruiz, A. L.; Lorenzon, W.; X. G., Lu; X. R., Lu; B. Q., Ma; Mahon, D.; Makins, N. C. R.; Manaenkov, S. I.; Manfre, L.; Mao, Y.; Marianski, B.; de la Ossa, A. M.; Marukyan, H.; Miller, C. A.; Miyachi, Y.; Movsisyan, A.; Muccifora, V.; Murray, M.; Mussgiller, A.; Nappi, E.; Naryshkin, Y.; Nass, A.; Negodaev, M.; Nowak, W. D.; Pappalardo, Luciano Libero; Perez Benito, R.; Pickert, N.; Raithel, M.; Reimer, P. E.; Reolon, A. R.; Riedl, C.; Rith, K.; Rosner, G.; Rostomyan, A.; Rubin, J.; Ryckbosch, D.; Salomatin, Y.; Sanftl, F.; Schafer, A.; Schnell, G.; Schuler, K. P.; Seitz, B.; Shibata, T. A.; Shutov, V.; Stancari, Michelle Dawn; Statera, Marco; Steffens, E.; Steijger, J. J. M.; Stenzel, H.; Stewart, J.; Stinzing, F.; Taroian, S.; Terkulov, A.; Trzcinski, A.; Tytgat, M.; Vandenbroucke, A.; van der Nat, P. B.; Haarlem, Y. v.; Hulse, C. V.; Veretennikov, D.; Vikhrov, V.; Vilardi, I.; Vogel, C.; Wang, S.; Yaschenko, S.; Ye, H.; Ye, Z.; Yen, S.; Yu, W.; Zeiler, D.; Zihlmann, B.; Zupranski, P.

doi:10.1007/JHEP06(2010)019

Polarisation asymmetries are measured for the hard exclusive leptoproduction of real photons from a longitudinally polarised hydrogen target. These asymmetries arise from the deeply virtual Compton scattering and Bethe-Heitler processes. From the data are extracted two asymmetries in the azimuthal distribution of produced real photons about the direction of the exchanged virtual photon: A(UL) with respect to the target polarisation and A(LL) with respect to the product of the beam and target polarisations. Results for both asymmetries are compared to the predictions from a generalised parton distribution model. The sin phi and cos(0 phi) amplitudes observed respectively for the A(UL) and A(LL) asymmetries are compatible with the sizeable predictions from the model. Unexpectedly, a sin(2 phi) modulation in the A(UL) asymmetry with a magnitude similar to that of the sin phi modulation is observed.