Dijet Angular Distribution in Photoproduction of Charm at HERA

Chekanov, S; Derrick, M; Krakauer, D; Loizides, Jh; Magill, S; Musgrave, B; Repond, J; Yoshida, R; Mattingly, Mck; Antonioli, P; Bari, G; Basile, M; Bellagamba, L; Boscherini, D; Bruni, A; Bruni, G; Romeo, Gc; Cifarelli, L; Cindolo, F; Contin, A; Corradi, M; DE PASQUALE, Salvatore; Giusti, P; Iacobucci, G; Margotti, A; Nania, R; Palmonari, F; Pesci, A; Sartorelli, G; Zichichi, A; Aghuzumtsyan, G; Bartsch, D; Brock, I; Goers, S; Hartmann, H; Hilger, E; Irrgang, P; Jakob, Hp; Kappes, A; Katz, Uf; Kind, O; Meyer, U; Paul, E; Rautenberg, J; Renner, R; Stifutkin, A; Tandler, J; Voss, Kc; Wang, M; Weber, A; Bailey, Ds; Brook, Nh; Cole, Je; Foster, B; Heath, Gp; Heath, Hf; Robins, S; Rodrigues, E; Scott, J; Tapper, Rj; Wing, M; Capua, M; Mastroberardino, A; Schioppa, M; Susinno, G; Kim, Jy; Kim, Yk; Lee, Jh; Lim, It; Pac, My; Caldwell, A; Helbich, M; Liu, X; Mellado, B; Ning, Y; Paganis, S; Ren, Z; Schmidke, W; Sciulli, F; Chwastowski, J; Eskreys, A; Figiel, J; Olkiewicz, K; Stopa, P; Zawiejski, L; Adamczyk, L; Bold, T; Grabowska Bold, I; Kisielewska, D; Kowal, Am; Kowal, M; Kowalski, T; Przybycien, M; Suszycki, L; Szuba, D; Szuba, J; Kotanski, A; Slominski, W; Bauerdick, Lat; Behrens, U; Boch, I; Borras, K; Chiochia, V; Dannheim, D; Drews, G; Fourletova, J; Fricke, U; Geiser, A; Goebel, F; Gottlicher, P; Gutsche, O; Haas, T; Hain, W; Hartner, Gf; Hillert, S; Kahle, B; Kotz, U; Kowalski, H; Kramberger, G; Labes, H; Lelas, D; Lohr, B; Mankel, R; Melzer Pellmann, Ia; Moritz, M; Nguyen, Cn; Notz, D; Petrucci, Mc; Polini, A; Raval, A; Schneekloth, U; Selonke, F; Wessoleck, H; Wolf, G; Youngman, C; Zeuner, W; Schlenstedt, S; Barbagli, G; Gallo, E; Genta, C; Pelfer, Pg; Bamberger, A; Benen, A; Coppola, N; Bell, M; Bussey, Pj; Doyle, At; Glasman, C; Hamilton, J; Hanlon, S; Lee, Sw; Lupi, A; Saxon, D; Skillicorn, Oi; Gialas, I; Bodmann, B; Carli, T; Holm, U; Klimek, K; Krumnack, N; Lohrmann, E; Milite, M; Salehi, H; Stonjek, S; Wick, K; Ziegler, A; Ziegler, A; Collins Tooth, C; Foudas, C; Goncalo, R; Long, Kr; Tapper, Ad; Cloth, P; Filges, D; Kuze, M; Nagano, K; Tokushuku, K; Yamada, S; Yamazaki, Y; Barakbaev, A; Boos, Eg; Pokrovskiy, Ns; Zhautykov, Bo; Lim, H; Son, D; Piotrzkowski, K; Barreiro, F; Gonzalez, O; Labarga, L; del Peso, J; Tassi, E; Terron, J; Vazquez, M; Barbi, M; Corriveau, F; Gliga, S; Lainesse, J; Padhi, S; Stairs, Dg; Tsurugai, T; Antonov, A; Danilov, P; Dolgoshein, Ba; Gladkov, D; Sosnovtsev, V; Suchkov, S; Dementiev, Rk; Ermolov, R; Golubkov, Ya; Katkov, Ii; Khein, La; Korzhavina, Ia; Kuzmin, Va; Levchenko, Bb; Lukina, Oy; Proskuryakov, As; Shcheglova, Lm; Vlasov, Nn; Zotkin, Sa; Coppola, N; Grijpink, S; Koffeman, E; Kooijman, K; Maddox, E; Pellegrino, A; Schagen, S; Tiecke, H; Tuning, N; Velthuis, Jj; Wiggers, L; de Wolf, E; Brummer, N; Bylsma, B; Durkin, Ls; Ling, Ty; Boogert, S; Cooper Sarkar, Am; Devenish, Rce; Ferrando, J; Grzelak, G; Patel, S; Rigby, M; Sutton, Mr; Walczak, R; Bertolin, A; Brugnera, R; Carlin, R; Dal Corso, F; Dusini, S; Garfagnini, A; Limentani, S; Longhin, A; Parenti, A; Posocco, P; Stanco, L; Turcato, M; Heaphy, Ea; Metlica, F; Oh, By; Saull, Prb; Whitmore, Jj; Iga, Y; D'Agostini, Gd; Marini, G; Nigro, A; Cormack, C; Hart, Jc; Mccubbin, Na; Heusch, C; Park, Ih; Pavel, N; Abramowicz, H; Gabareen, A; Kananov, S; Kreisel, A; Levy, A; Abe, T; Fusayasu, T; Kagawa, S; Kohno, T; Tawara, T; Yamashita, T; Hamatsu, R; Hirose, T; Inuzuka, M; Kitamura, S; Matsuzawa, K; Nishimura, T; Arneodo, M; Ferrero, Mi; Monaco, V; Ruspa, M; Sacchi, R; Solano, A; Koop, T; Levman, Gm; Martin, Jf; Mirea, A; Butterworth, Jm; Gwenlan, C; Hall Wilton, R; Jones, Tw; Lightwood, Ms; West, Bj; Ciborowski, J; Ciesielski, R; Nowak, Rj; Pawlak, Jm; Sztuk, J; Tymieniecka, T; Ukleja, A; Ukleja, J; Zarnecki, Af; Adamus, M; Plucinski, P; Eisenberg, Y; Gladilin, Lk; Hochman, D; Karshon, U; Kcira, D; Lammers, S; Li, L; Reeder, Dd; Savin, Aa; Smith, Wh; Deshpande, A; Dhawan, S; Hughes, Vw; Straub, Pb; Bhadra, S; Catterall, Cd; Fourletov, S; Menary, S; Soares, M; Standage, J.

doi:10.1016/S0370-2693(03)00752-4

Dijet angular distributions of photoproduction events in which a D*± meson is produced in association with one of two energetic jets have been measured with the ZEUS detector at HERA, using an integrated luminosity of 120 pb-1. Differential cross sections as a function of the angle between the charm-jet and the proton-beam direction in the dijet rest frame have been measured for samples enriched in direct or resolved photon events. The results are compared with predictions from leading-order parton-shower Monte Carlo models and with next-to-leading-order QCD calculations. The angular distributions show clear evidence for the existence of charm originating from the photon.