Elastic J / ψ Production at HERA H 1 Collaboration

Cross sections for elastic production of J/ψ mesons in photoproduction and electroproduction are measured in electron proton collisions at HERA u sing an integrated luminosity of 55 pb−1. Results are presented for photon virtualities Q2 up to 80GeV. The dependence on the photon-proton centre of mass energy Wγp is analysed in the range 40 ≤ Wγp ≤ 305GeV in photoproduction and40 ≤ Wγp ≤ 160GeV in electroproduction. TheWγp dependences of the cross sections do not change significantl y with Q2 and can be described by models based on perturbative QCD. Within such models, the data show a high sensitivity to the gluon density of the proton in the do main of low Bjorkenx and low Q2 . Differential cross sections d σ/dt, wheret is the squared four-momentum transfer at the proton vertex, are measured in the range |t| < 1.2GeV as functions ofWγp andQ2. Effective Pomeron trajectories are determined for photopr duction and electroproduction. TheJ/ψ production and decay angular distributions are consistent with s-channel helicity conservation. The ratio of the cross sections for longitudi nally and transversely polarised photons is measured as a function of Q2 and is found to be described by perturbative QCD based models. Submitted toEur. Phys. J.C A. Aktas, V. Andreev, T. Anthonis, B. Antunovic, S. Aplin, A. Asmone, A. Astvatsatourov , A. Babaev, S. Backovic, J. Bähr , A. Baghdasaryan , P. Baranov , E. Barrelet , W. Bartel, S. Baudrand , S. Baumgartner , J. Becker , M. Beckingham, O. Behnke, O. Behrendt , A. Belousov, Ch. Berger , N. Berger , J.C. Bizot , M. -O. Boenig, V. Boudry, J. Bracinik, G. Brandt , V. Brisson, D. Bruncko, F.W. Büsser , A. Bunyatyan, G. Buschhorn, L. Bystritskaya, A.J. Campbell , S. Caron, F. Cassol-Brunner , K. Cerny, V. Cerny, V. Chekelian, J.G. Contreras , J.A. Coughlan, B.E. Cox, G. Cozzika, J. Cvach, J.B. Dainton, W.D. Dau, K. Daum, Y. de Boer , B. Delcourt, M. Del Degan, A. De Roeck, K. Desch, E.A. De Wolf, C. Diaconu, V. Dodonov, A. Dubak, G. Eckerlin, V. Efremenko, S. Egli, R. Eichler, F. Eisele, M. Ellerbrock, E. Elsen, W. Erdmann, S. Essenov , A. Falkewicz, P.J.W. Faulkner , L. Favart, A. Fedotov, R. Felst , J. Ferencei , L. Finke, M. Fleischer , P. Fleischmann , G. Flucke, A. Fomenko, I. Foresti , G. Franke, T. Frisson, E. Gabathuler , E. Garutti , J. Gayler , C. Gerlich, S. Ghazaryan , S. Ginzburgskaya , A. Glazov, I. Glushkov, L. Goerlich, M. Goettlich, N. Gogitidze, S. Gorbounov , C. Goyon, C. Grab, T. Greenshaw, M. Gregori, B.R. Grell, G. Grindhammer , C. Gwilliam, D. Haidt, L. Hajduk, M. Hansson, G. Heinzelmann , R.C. W. Henderson , H. Henschel , O. Henshaw, G. Herrera, M. Hildebrandt , K.H. Hiller, D. Hoffmann, R. Horisberger , A. Hovhannisyan , T. Hreus, S. Hussain, M. Ibbotson, M. Ismail, M. Jacquet , L. Janauschek , X. Janssen , V. Jemanov , L. Jönsson, D.P. Johnson , A.W. Jung, H. Jung, M. Kapichine, J. Katzy, I.R. Kenyon, C. Kiesling, M. Klein, C. Kleinwort, T. Klimkovich, T. Kluge, G. Knies, A. Knutsson, V. Korbel, P. Kostka, K. Krastev, J. Kretzschmar , A. Kropivnitskaya, K. Krüger, J. Kückens, M.P.J. Landon , W. Lange, T. Laštovička, G. Laštovička-Medin , P. Laycock, A. Lebedev, G. Leibenguth, V. Lendermann, S. Levonian, L. Lindfeld, K. Lipka, A. Liptaj, B. List, J. List, E. Lobodzinska, N. Loktionova, R. Lopez-Fernandez , V. Lubimov, A. -I. Lucaci-Timoce, H. Lueders, D. Lüke, T. Lux, L. Lytkin, A. Makankine, N. Malden, E. Malinovski, S. Mangano , P. Marage, R. Marshall , M. Martisikova, H. -U. Martyn, S.J. Maxfield, D. Meer, A. Mehta, K. Meier, A.B. Meyer, H. Meyer, J. Meyer , S. Mikocki, I. Milcewicz-Mika, D. Milstead, D. Mladenov, A. Mohamed, F. Moreau, A. Morozov, J.V. Morris, M.U. Mozer, K. Müller, P. Murı́n, K. Nankov, B. Naroska, Th. Naumann , P.R. Newman , C. Niebuhr , A. Nikiforov, D. Nikitin, G. Nowak, M. Nozicka, R. Oganezov , B. Olivier, J.E. Olsson, S. Osman, D. Ozerov, V. Palichik, I. Panagoulias , T. Papadopoulou , C. Pascaud , G.D. Patel , M. Peez, E. Perez , D. Perez-Astudillo, A. Perieanu, A. Petrukhin, D. Pitzl, R. Plačakytė , B. Portheault , B. Povh, P. Prideaux , A.J. Rahmat , N. Raicevic, P. Reimer , A. Rimmer, C. Risler, E. Rizvi, P. Robmann , B. Roland, R. Roosen, A. Rostovtsev, Z. Rurikova, S. Rusakov , F. Salvaire, D.P.C. Sankey , E. Sauvan , S. Schätzel , F. -P. Schilling, D. Schmidt , S. Schmidt , S. Schmitt , C. Schmitz, L. Schoeffel , A. Schöning, H. -C. Schultz-Coulon , K. Sedlák, F. Sefkow, R.N. Shaw-West , I. Sheviakov, L.N. Shtarkov, T. Sloan, P. Smirnov, Y. Soloviev, D. South, V. Spaskov, A. Specka, B. Stella, J. Stiewe, I. Strauch, U. Straumann , V. Tchoulakov, G. Thompson, P.D. Thompson , F. Tomasz , D. Traynor, P. Truöl, I. Tsakov, G. Tsipolitis, I. Tsurin, J. Turnau, E. Tzamariudaki , M. Urban, A. Usik,