Abstract
The diffractive photoproduction of rho mesons, e p \to e rho Y, with large momentum transfer squared at the proton vertex, |t|, is studied with the H1 detector at HERA using an integrated luminosity of 20.1 pb^{-1}. The photon-proton centre of mass energy spans the range 75 < W < 95 GeV, the photon virtuality is restricted to Q^2 < 0.01 GeV^2 and the mass M_Y of the proton remnant is below 5 GeV. The t dependence of the cross section is measured for the range 1.5 < |t| < 10.0 GeV^2 and is well described by a power law, dsigma/ d|t| \propto |t|^{-n}. The spin density matrix elements, which provide information on the helicity structure of the interaction, are extracted using measurements of angular distributions of the rho decay products. The data indicate a violation of s-channel helicity conservation, with contributions from both single and double helicity-flip being observed. The results are compared to the predictions of perturbative QCD models.
Highlights
Diffractive vector meson production in ep interactions with large negative four-momentum transfer squared at the proton vertex, t, provides a powerful means to probe the nature of the diffractive exchange
The data presented in this Letter are compared to two theoretical predictions: A fixed order calculation in which the hard interaction is approximated by the exchange of two gluons,13 and a leading logarithm (LL) calculation in which it is described according to the BFKL evolution
In the case of the LL BFKL model, the helicity amplitudes are predicted to follow a hierarchical structure with |M++| > |M+−| > |M+0| [9,10]
Summary
C. Risler i, E. Rizvi r, P. Robmann an, B. Roland c, R. Roosen c, A. Rostovtsev x, Z. Rurikova z, S. Rusakov y, F. Salvaire j, D.P.C. Sankey d, E. Sauvan u, S. Schätzel i, S. Schmidt i, S. Schmitt i, C. Schmitz an, L. Schoeffel h, A. Schöning am, H.-C. Schultz-Coulon m, F. Sefkow i, R.N. Shaw-West b, I. Sheviakov y, L.N. Shtarkov y, T. Sloan p, P. Smirnov y, Y. Soloviev y, D. South i, V. Spaskov g, A. Specka ab, M. Steder i, B. Stella ag, J. Stiewe m, U. Straumann an, D. Sunar c, V. Tchoulakov g, G. Thompson r, P.D. Thompson b, T. Toll i, F. Tomasz o, D. Traynor r, P. Truöl an, I. Tsakov ah, G. Tsipolitis i,ao, I. Tsurin i, J. Turnau e, E. Tzamariudaki z, K. Urban m, M. Urban an, A. Usik y, D. Utkin x, A. Valkárová af, C. Vallée u, P. Van Mechelen c, A. Vargas Trevino f, Y. Vazdik y, C. Veelken q, S. Vinokurova i, V. Volchinski ak, K. Wacker f, G. Weber j, R. Weber am, D. Wegener f, C. Werner l, M. Wessels i, B. Wessling i, Ch. Wissing f, R. Wolf l, E. Wünsch i, S. Xella an, W. Yan i, V. Yeganov ak, J. Žácek af, J. Zálešák ae, Z. Zhang aa, A. Zhelezov x, A. Zhokin x, Y.C. Zhu i, J. Zimmermann z, T. Zimmermann am, H. Zohrabyan ak, F. Zomer aa a I. Physikalisches Institut der RWTH, Aachen, Germany 1 b School of Physics and Astronomy, University of Birmingham, Birmingham, UK 2 c Inter-University Institute for High Energies ULB-VUB, and Universiteit Antwerpen, Antwerpen, Belgium 3 d Rutherford Appleton Laboratory, Chilton, Didcot, UK 2 e Institute for Nuclear Physics, Cracow, Poland 4 f Institut für Physik, Universität Dortmund, Dortmund, Germany 1 g Joint Institute for Nuclear Research, Dubna, Russia h CEA, DSM/DAPNIA, CE-Saclay, Gif-sur-Yvette, France i DESY, Hamburg, Germany j Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany 1 k Max-Planck-Institut für Kernphysik, Heidelberg, Germany l Physikalisches Institut, Universität Heidelberg, Heidelberg, Germany 1 m Kirchhoff-Institut für Physik, Universität Heidelberg, Heidelberg, Germany 1 n Institut für Experimentelle und Angewandte Physik, Universität Kiel, Kiel, Germany o Institute of Experimental Physics, Slovak Academy of Sciences, Košice, Slovak Republic 6 p Department of Physics, University of Lancaster, Lancaster, UK 2 q Department of Physics, University of Liverpool, Liverpool, UK 2 r Queen Mary and Westfield College, London, UK 2 s Physics Department, University of Lund, Lund, Sweden 7 t Physics Department, University of Manchester, Manchester, UK 2 u CPPM, CNRS/IN2P3, University of Mediterranee, Marseille, France v Departamento de Fisica Aplicada, CINVESTAV, Mérida, Yucatán, Mexico 10 w Departamento de Fisica, CINVESTAV, Mexico 10 x Institute for Theoretical and Experimental Physics, Moscow, Russia 11 y Lebedev Physical Institute, Moscow, Russia 5 z Max-Planck-Institut für Physik, München, Germany aa LAL, Université de Paris-Sud, IN2P3-CNRS, Orsay, France ab LLR, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France ac LPNHE, Universités Paris VI and VII, IN2P3-CNRS, Paris, France ad Faculty of Science, University of Montenegro, Podgorica, Serbia and Montenegro 5 ae Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic 8 af Faculty of Mathematics and Physics, Charles University, Praha, Czech Republic 8 ag Dipartimento di Fisica Università di Roma Tre and INFN Roma 3, Roma, Italy ah Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria 5 ai Paul Scherrer Institut, Villigen, Switzerland aj Fachbereich C, Universität Wuppertal, Wuppertal, Germany ak Yerevan Physics Institute, Yerevan, Armenia al DESY, Zeuthen, Germany am Institut für Teilchenphysik, ETH, Zürich, Switzerland 9 an Physik-Institut der Universität Zürich, Zürich, Switzerland 9 ao Physics Department, National Technical University, Zografou Campus, GR-15773 Athens, Greece ap Rechenzentrum, Universität Wuppertal, Wuppertal, Germany aq University of P.J. Šafárik, Košice, Slovak Republic ar CERN, Geneva, Switzerland as Max-Planck-Institut für Physik, München, Germany at Comenius University, Bratislava, Slovak Republic Received 21 March 2006; accepted 17 May 2006 Available online 21 June 2006 Editor: W.-D. Schlatter
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