Measurement of diffractive photoproduction of vector mesons at large momentum transfer at HERA

  • The ZEUS Collaboration
  • J. Breitweg et al.
Experimental physics


Elastic and proton–dissociative photoproduction of \(\rho^0\), \(\phi\) and \(J/\psi\) vector mesons (\(\gamma p\rightarrow Vp\), \(\gamma p\rightarrow VN\), respectively) have been measured in \(e^+p\) interactions at HERA up to \(-t=3\) GeV\(^2\), where t is the four-momentum transfer squared at the photon–vector–meson vertex. The analysis is based on a data sample in which photoproduction reactions were tagged by detection of the scattered positron in a special-purpose calorimeter. This limits the photon virtuality, \(Q^2\), to values less than 0.01 GeV\(^2\), and selects a \(\gamma p\) average center-of-mass energy of \(\langle W\rangle\) = 94 GeV. Results for the differential cross sections, \(\mbox{d}\sigma/\mbox{d}t\), for \(\rho^0\), \(\phi\) and \(J/\psi\) mesons are presented and compared to the results of recent QCD calculations. Results are also presented for the t-dependence of the pion-pair invariant-mass distribution in the \(\rho^0\) mass region and of the spin-density matrix elements determined from the decay-angle distributions. The Pomeron trajectory has been derived from measurements of the W dependence of the elastic differential cross sections \(\mbox{d}\sigma/\mbox{d}t\) for both \(\rho^0\) and \(\phi\) mesons.


Matrix Element Momentum Transfer Differential Cross Section Vector Meson Differential Cross 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • The ZEUS Collaboration
  • J. Breitweg et al.
    • 1
  1. 1.Argonne National Laboratory, Argonne, IL, USA US

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