Abstract
The diffractive photoproduction of J/ψ mesons is measured with the H1 detector at the ep collider HERA using an integrated luminosity of 78 pb−1. The differential cross section dσ(γp→J/ψY)/dt is studied in the range 2<|t|<30 GeV2, where t is the square of the four-momentum transferred at the proton vertex. The cross section is also presented as a function of the photon–proton centre-of-mass energy Wγp in three t intervals, spanning the range 50<Wγp<200 GeV. A fast rise of the cross section with Wγp is observed for each t range and the slope for the effective linear Pomeron trajectory is measured to be α′=−0.0135±0.0074(stat.)±0.0051(syst.) GeV−2. The measurements are compared with perturbative QCD models based on BFKL and DGLAP evolution. The data are found to be compatible with s-channel helicity conservation.
Highlights
The diffractive photoproduction of J /ψ mesons with large negative momentum transfer squared t at the proton vertex is a powerful means to probe the parton dynamics of the diffractive exchange
The diffractive photoproduction of vector mesons can be modelled in the proton rest frame, where the photon fluctuates into a qqpair at a long distance from the proton target
Compared with other channels which have been used to search for BFKL evolution [3,4,5,6,7,8], the measurement of diffractive J /ψ production at large |t| provides an experimentally clean signature in which the accurate measurement of the J /ψ fourmomentum allows the kinematic dependences of the process to be determined precisely
Summary
Q School of Physics and Chemistry, University of Lancaster, Lancaster, UK 9 r Department of Physics, University of Liverpool, Liverpool, UK 9 s Queen Mary and Westfield College, London, UK 9 t Physics Department, University of Lund, Lund, Sweden 14 u Physics Department, University of Manchester, Manchester, UK 9 v CPPM, CNRS/IN2P3, University Mediterranee, Marseille, France w Institute for Theoretical and Experimental Physics, Moscow, Russia 18 x Lebedev Physical Institute, Moscow, Russia 12 y Max-Planck-Institut für Physik, München, Germany z LAL, Université de Paris-Sud, IN2P3-CNRS, Orsay, France aa LPNHE, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France ab LPNHE, Universités Paris VI and VII, IN2P3-CNRS, Paris, France ac Institute of Physics, Academy of Sciences of the Czech Republic, Praha, Czech Republic 12,15 ad Faculty of Mathematics and Physics, Charles University, Praha, Czech Republic 12,15 ae Dipartimento di Fisica Università di Roma Tre and INFN Roma 3, Roma, Italy af Paul Scherrer Institut, Villigen, Switzerland ag Fachbereich Physik, Bergische Universität Gesamthochschule Wuppertal, Wuppertal, Germany ah Yerevan Physics Institute, Yerevan, Armenia ai DESY, Zeuthen, Germany aj Institut für Teilchenphysik, ETH, Zürich, Switzerland 16 ak Physik-Institut der Universität Zürich, Zürich, Switzerland 16
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