The dependence of dijet production on photon virtuality in ep collisions at HERA

Chekanov, S.; Derrick, M.; Magill, S.; Miglioranzi, S.; Musgrave, B.; Repond, J.; Yoshida, R.; Mck, Mattingly; Pavel, N.; Agy, Molina; 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, S.; Giusti, P.; Iacobucci, G.; Margotti, A.; Montanari, A.; Nania, R.; Palmonari, F.; Pesci, A.; Polini, A.; Rinaldi, L.; Sartorelli, G.; Zichichi, A.; Aghuzumtsyan, G.; Bartsch, D.; Brock, I.; Goers, S.; Hartmann, H.; Hilger, E.; Irrgang, P.; Jakob, Hp; Kind, O.; Meyer, U.; Paul, E.; Rautenberg, J.; Renner, R.; Voss, Kc; Wang, M.; Wlasenko, M.; Bailey, Ds; Brook, Nh; Cole, Je; Heath, Gp; Namsoo, T.; Robins, S.; Capua, M.; Mastroberardino, A.; Schioppa, M.; Susinno, G.; Tassi, E.; Kim, Jy; Kj, Ma; Helbich, M.; Ning, Y.; Ren, Z.; Schmidke, Wb; Sciulli, E.; Chwastowski, J.; Eskreys, A.; Figiel, J.; Galas, A.; Olkiewicz, K.; Stopa, P.; Szuba, D.; Zawiejski, L.; Adamczyk, L.; Bold, T.; Grabowska Bold, I.; Kisielewska, D.; Kowal, Am; Lukasik, J.; Przybycien, M.; Suszycki, L.; Szuba, J.; Kotanski, A.; Slominski, W.; Adler, V.; Behrens, U.; Bloch, I.; Borras, K.; Cassel, Dg; Drews, G.; Fourletova, J.; Geiser, A.; Gladkov, D.; Goebel, F.; Gottlicher, P.; Diaz, Rg; Gutsche, O.; Haas, T.; Hain, W.; Horn, C.; Kahle, B.; Kasemann, M.; Kotz, U.; Kowalski, H.; Kramberger, G.; Lelas, D.; Lim, H.; Lohr, B.; Mankel, R.; Martinez, M.; Melzer Pellmann IA,; Nguyen, Cn; Notz, D.; Nuncio Quiroz AE,; Raval, A.; Santamarta, R.; Schneekloth, U.; Stosslein, U.; Wolf, G.; Youngman, C.; Zeuner, W.; Schlenstedt, S.; Barbagli, G.; Gallo, E.; Genta, C.; Pelfer, Pg; Bamberger, A.; Benen, A.; Karstens, F.; Dobur, D.; Vlasov, Nn; Bussey, Pj; Doyle, At; Ferr, o. J.; Hamilton, J.; Hanlon, S.; Saxon, Dh; Skillicorn, Io; Gialas, I.; Carli, T.; Gosau, T.; Holm, U.; Krumnack, N.; Lohrmann, E.; Milite, M.; Salehi, H.; Schleper, P.; Schorner Sadenius, T.; Stonjek, S.; Wichmann, K.; Wick, K.; Ziegler, A.; Ziegler, A.; Collins Tooth, C.; Foudas, C.; Fry, C.; Goncalo, R.; Long, Kr; Tapper, Ad; Kataoka, M.; Nagano, K.; Tokushuku, K.; Yamada, S.; Yamazakai, Y.; Barakbaev, An; Boos, Eg; Pokrovskiy, Ns; Zhautykov, Bo; Son, D.; de Favereau, J.; Piotrzkowski, K.; Barreiro, F.; Glasman, C.; Gonzalez, O.; Jimenez, M.; Labarga, L.; del Peso, J.; Terron, J.; Zambrana, M.; Barbi, M.; Corriveau, F.; Liu, C.; Padhi, S.; Plamondon, M.; Stairs, Dg; Walsh, R.; Zhou, C.; Tsurugai, T.; Antonov, A.; Danilov, P.; Dolgoshein, Ba; Sosnovtsev, V.; Stifutkin, A.; Suchkov, S.; Dementiev, Rk; Ermolov, R.; Gladilin, Lk; Katkov, Ii; Khein, La; Korzhavina, Ia; Kuzmin, Va; Levchenko, Bb; Lukina, Oy; Proskuryakov, As; Shcheglova, Lm; Zotkin, Ds; Zotkin, Sa; Abt, I.; Buttner, C.; Caldwell, A.; Liu, X.; Sutiak, J.; Coppola, N.; Grigorescu, G.; Grijpink, S.; Keramidas, A.; Koffeman, E.; Kooijman, P.; Maddox, E.; Pellegrino, A.; Schagen, S.; Tiecke, H.; Vazquez, M.; Wiggers, L.; de Wolf, E.; Brummer, N.; Bylsma, B.; Durkin, Ls; Ling, Ty; Allfrey, Pd; Bell, Ma; Cooper Sarkar AM,; Cottrell, A.; Rce, Devenish; Foster, B.; Grzelak, G.; Gwenlan, C.; Kohno, T.; Patel, S.; Straub, Pb; Walczak, R.; Bellan, P.; Bertolin, A.; Brugnera, R.; Carlin, R.; Ciesielski, R.; Dal Corso, F.; Dusini, S.; Garfagnini, A.; Limentani, S.; Longhin, A.; Stanco, L.; Turcato, M.; Heaphy, Ea; Metlica, F.; By, Oh; Whitmore, Jj; Iga, Y.; D'Agostini, G.; Marini, G.; Nigro, A.; Hart, Jc; Abramowicz, H.; Gabareen, A.; Groys, M.; Kananov, S.; Kreisel, A.; Levy, A.; Kuze, M.; Kagawa, S.; Tawara, T.; Hamatsu, R.; Kaji, H.; Kitamura, S.; Matsuzawa, K.; Ota, O.; Yd, Ri; Costa, Marco; Ferrero, Mi; Monaco, Vincenzo; Sacchi, Roberto; Solano, Ada Maria; Arneodo, M.; Ruspa, M.; Fourletov, S.; Koop, T.; Martin, Jf; Mirea, A.; Butterworth, Jm; Hall Wilton, R.; Jones, Tw; Loizides, Jh; Sutton, Mr; Targett Adams, C.; Wing, M.; Ciborowski, J.; Kulinski, P.; Luzniak, P.; Malka, J.; Nowak, Rj; Pawlak, Jm; Sztuk, J.; Tymieniecka, T.; Tyszkiewicz, A.; Ukleja, A.; Ukleja, J.; Zarnecki, Af; Adamus, M.; Plucinski, P.; Eisenberg, Y.; Hochman, D.; Karshon, U.; Lightwood, Ms; Everett, A.; Kcira, D.; Lammers, S.; Li, L.; Reeder, Dd; Rosin, M.; Ryan, P.; Savin, Aa; Smith, Wh; Dhawan, S.; Bhadra, S.; Catterall, Cd; Cui, Y.; Hartner, G.; Menary, S.; Noor, U.; Soares, M.; St,; Age, J.; Whyte, J.

doi:10.1140/epjc/s2004-01885-2

The dependence of dijet production on the virtuality of the exchanged photon, Q2, has been studied by measuring dijet cross sections in the range 0 < Q^2 < 2000 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb -1. Dijet cross sections were measured for jets with transverse energy E_T^jet>7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range -3<\eta^jet<0. The variable x_gamma^obs, a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q2 dependence of the ratio of low- to high- x_gamma^obs events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low- x_gamma^obs contribution relative to that at high x_gamma^obs. Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q2, provide a qualitative description of the data.