Elastic Electroproduction of � Mesons at HERA H 1 Collaboration

The elastic electroproduction of mesons is studied at HERA with the H1 detector for a photon virtuality in the range and for a hadronic centre of mass energy in the range GeV. The shape of the ( ) mass distribution in the resonance region is measured as a function of . The full set of spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of "!# $ of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on , and % (the four-momentum transfer squared to the proton). They suggest that, especially at large , the & ')( cross section develops a stronger dependence than that expected from the behaviour of elastic and total hadron * hadron cross sections. To be submitted to Eur. Phys. J. C. C. Adloff , V. Andreev , B. Andrieu , V. Arkadov , A. Astvatsatourov , I. Ayyaz , A. Babaev , J. Bähr , P. Baranov , E. Barrelet , W. Bartel , U. Bassler , P. Bate , A. Beglarian , O. Behnke , H.-J. Behrend , C. Beier , A. Belousov , Ch. Berger , G. Bernardi , T. Berndt , G. Bertrand-Coremans , P. Biddulph , J.C. Bizot , V. Boudry , W. Braunschweig , V. Brisson , D.P. Brown , W. Brückner , P. Bruel , D. Bruncko , J. Bürger , F.W. Büsser , A. Buniatian , S. Burke , A. Burrage , G. Buschhorn , D. Calvet , A.J. Campbell , T. Carli , E. Chabert , M. Charlet , D. Clarke , B. Clerbaux , J.G. Contreras , C. Cormack , J.A. Coughlan , M.C. Cousinou , B.E. Cox , G. Cozzika , J. Cvach , J.B. Dainton , W.D. Dau , K. Daum , M. David , M. Davidsson , A. De Roeck , E.A. De Wolf , B. Delcourt , R. Demirchyan , C. Diaconu , M. Dirkmann , P. Dixon , W. Dlugosz , K.T. Donovan , J.D. Dowell , A. Droutskoi , J. Ebert , G. Eckerlin , D. Eckstein , V. Efremenko , S. Egli , R. Eichler , F. Eisele , E. Eisenhandler , E. Elsen , M. Enzenberger , M. Erdmann , A.B. Fahr , P.J.W. Faulkner , L. Favart , A. Fedotov , R. Felst , J. Feltesse , J. Ferencei , F. Ferrarotto , M. Fleischer , G. Flügge , A. Fomenko , J. Formánek , J.M. Foster , G. Franke , E. Gabathuler , K. Gabathuler , F. Gaede , J. Garvey , J. Gassner , J. Gayler , R. Gerhards , S. Ghazaryan , A. Glazov , L. Goerlich , N. Gogitidze , M. Goldberg , I. Gorelov , C. Grab , H. Grässler , T. Greenshaw , R.K. Griffiths , G. Grindhammer , T. Hadig , D. Haidt , L. Hajduk , M. Hampel , V. Haustein , W.J. Haynes , B. Heinemann , G. Heinzelmann , R.C.W. Henderson , S. Hengstmann , H. Henschel , R. Heremans , I. Herynek , K. Hewitt , K.H. Hiller , C.D. Hilton , J. Hladký , D. Hoffmann , R. Horisberger , S. Hurling , M. Ibbotson , Ç. İşsever , M. Jacquet , M. Jaffre , L. Janauschek , D.M. Jansen , L. Jönsson , D.P. Johnson , M. Jones , H. Jung , H.K. Kästli , M. Kander , D. Kant , M. Kapichine , M. Karlsson , O. Karschnik , J. Katzy , O. Kaufmann , M. Kausch , N. Keller , I.R. Kenyon , S. Kermiche , C. Keuker , C. Kiesling , M. Klein , C. Kleinwort , G. Knies , J.H. Köhne , H. Kolanoski , S.D. Kolya , V. Korbel , P. Kostka , S.K. Kotelnikov , T. Krämerkämper , M.W. Krasny , H. Krehbiel , D. Krücker , K. Krüger , A. Küpper , H. Küster , M. Kuhlen , T. Kurča , W. Lachnit , R. Lahmann , D. Lamb , M.P.J. Landon , W. Lange , U. Langenegger , A. Lebedev , F. Lehner , V. Lemaitre , R. Lemrani , V. Lendermann , S. Levonian , M. Lindstroem , G. Lobo , E. Lobodzinska , V. Lubimov , S. Lüders , D. Lüke , L. Lytkin , N. Magnussen , H. Mahlke-Krüger , N. Malden , E. Malinovski , I. Malinovski , R. Maraček , P. Marage , J. Marks , R. Marshall , H.-U. Martyn , J. Martyniak , S.J. Maxfield , T.R. McMahon , A. Mehta , K. Meier , P. Merkel , F. Metlica , A. Meyer , A. Meyer , H. Meyer , J. Meyer , P.-O. Meyer , S. Mikocki , D. Milstead , R. Mohr , S. Mohrdieck , M. Mondragon , F. Moreau , A. Morozov , J.V. Morris , D. Müller , K. Müller , P. Murı́n , V. Nagovizin , B. Naroska , J. Naumann , Th. Naumann , I. Négri , P.R. Newman , H.K. Nguyen , T.C. Nicholls , F. Niebergall , C. Niebuhr , Ch. Niedzballa , H. Niggli , O. Nix , G. Nowak , T. Nunnemann , H. Oberlack , J.E. Olsson , D. Ozerov , P. Palmen , V. Panassik , C. Pascaud , S. Passaggio , G.D. Patel , H. Pawletta , E. Perez , J.P. Phillips , A. Pieuchot , D. Pitzl , R. Pöschl , G. Pope , B. Povh , K. Rabbertz , J. Rauschenberger , P. Reimer , B. Reisert , D. Reyna , H. Rick , S. Riess , E. Rizvi , P. Robmann , R. Roosen , K. Rosenbauer , A. Rostovtsev , F. Rouse , C. Royon , S. Rusakov , K. Rybicki , D.P.C. Sankey , P. Schacht , J. Scheins , F.-P. Schilling , S. Schleif , P. Schleper , D. Schmidt , D. Schmidt , L. Schoeffel , V. Schröder , H.-C. Schultz-Coulon , F. Sefkow , A. Semenov , V. Shekelyan , I. Sheviakov , L.N. Shtarkov , G. Siegmon , Y. Sirois , T. Sloan , P. Smirnov , M. Smith , V. Solochenko , Y. Soloviev , V. Spaskov , A. Specka , H. Spitzer , F. Squinabol , R. Stamen , P. Steffen , R. Steinberg , J. Steinhart , B. Stella , A. Stellberger , J. Stiewe , U. Straumann , W. Struczinski , J.P. Sutton , M. Swart , S. Tapprogge , 1 M. Taševský , V. Tchernyshov , S. Tchetchelnitski , J. Theissen , G. Thompson , P.D. Thompson , N. Tobien , R. Todenhagen , D. Traynor , P. Truöl , G. Tsipolitis , J. Turnau , E. Tzamariudaki , S. Udluft , A. Usik , S. Valkár , A. Valkárová , C. Vallée , P. Van Esch , A. Van Haecke , P. Van Mechelen , Y. Vazdik , G. Villet , K. Wacker , R. Wallny , T. Walter , B. Waugh , G. Weber , M. Weber , D. Wegener , A. Wegner , T. Wengler , M. Werner , L.R. West , G. White , S. Wiesand , T. Wilksen , S. Willard , M. Winde , G.-G. Winter , Ch. Wissing , C. Wittek , E. Wittmann , M. Wobisch , H. Wollatz , E. Wünsch , J. Žáček , J. Zálešák , Z. Zhang , A. Zhokin , P. Zini , F. Zomer , J. Zsembery and M. zur Nedden I. Physikalisches Institut der RWTH, Aachen, Germany III. Physikalisches Institut der RWTH, Aachen, Germany School of Physics and Space Research, University of Birmingham, Birmingham, UK Inter-University Institute for High Energies ULB-VUB, Brussels; Universitaire Instelling Antwerpen, Wilrijk; Belgium Rutherford Appleton Laboratory, Chilton, Didcot, UK Institute for Nuclear Physics, Cracow, Poland Physics Department and IIRPA, University of California, Davis, California, USA Institut für Physik, Universität Dortmund, Dortmund, Germany Joint Institute for Nuclear Research, Dubna, Russia DSM/DAPNIA, CEA/Saclay, Gif-sur-Yvette, France DESY, Hamburg, Germany II. Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany Max-Planck-Institut für Kernphysik, Heidelberg, Germany Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany Institut für Hochenergiephysik, Universität Heidelberg, Heidelberg, Germany Institut für experimentelle und angewandte Physik, Universität Kiel, Kiel, Germany Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovak Republic School of Physics and Chemistry, University of Lancaster, Lancaster, UK Department of Physics, University of Liverpool, Liverpool, UK Queen Mary and Westfield College, London, UK Physics Department, University of Lund, Lund, Sweden Department of Physics and Astronomy, University of Manchester, Manchester, UK CPPM, Université d’Aix-Marseille II, IN2P3-CNRS, Marseille, France Institute for Theoretical and Experimental Physics, Moscow, Russia Lebedev Physical Institute, Moscow, Russia Max-Planck-Institut für Physik, München, Germany LAL, Université de Paris-Sud, IN2P3-CNRS, Orsay, France LPNHE, École Polytechnique, IN2P3-CNRS, Palaiseau, France LPNHE, Universités Paris VI and VII, IN2P3-CNRS, Paris, France Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic Nuclear Center, Charles University, Praha, Czech Republic INFN Roma 1 and Dipartimento di Fisica, Università Roma 3, Roma, Italy Paul Scherrer Institut, Villigen, Switzerland Fachbereich Physik, Bergische Universität Gesamthochschule Wuppertal, Wuppertal, Germany DESY, Institut für Hochenergiephysik, Zeuthen, Germany Institut für Teilchenphysik, ETH, Zürich, Switzerland Physik-Institut der Universität Zürich, Zürich, Switzerland 2 Institut für Physik, Humboldt-Universität, Berlin, Germany Rechenzentrum, Bergische Universität Gesamthochschule Wuppertal, Wuppertal, Germany Vistor from Yerevan Physics Institute, Armenia Foundation for Polish Science fellow Institut für Experimentelle Kernphysik, Universität Karlsruhe, Karlsruhe, Germany Dept. Fis. Ap. CINVESTAV, Mérida, Yucatán, México Supported by the Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie, FRG, under contract numbers 7AC17P, 7AC47P, 7DO55P, 7HH17I, 7HH27P, 7HD17P, 7HD27P, 7KI17I, 6MP17I and 7WT87P Supported by the UK Particle Physics and Astronomy Research Council, and formerly by the UK Science and Engineering Research Council Supported by FNRS-FWO, IISN-IIKW Partially supported by the Polish State Committee for Scientific Research, grant no. 115/E343/SPUB/P03/002/97 and grant no. 2P03B 055 13 Supported in part by US DOE grant DE F603 91ER40674 Supported by the Deutsche Forschungsgemeinschaft Supported by the Swedish Natural Science Research Council Supported by GA ČR grant no. 202/96/0214, GA AV ČR grant no. A1010821 and GA UK grant no. 177 Supported by the Swiss National Science Foundation Supported by VEGA SR grant no. 2/5167/98 Supported by Russian Foundation for Basic Research grant no. 96-02-00019