| Abstract | Exclusive diffractive photoproduction of J/psi mesons is measured with
the H1 detector at the electron-proton collider HERA. At the end of the
HERA operation in 2007 the nominal proton beam energy was reduced from
920 GeV to 575 and 460 GeV, respectively. The reduced proton beam energy
allows diffractive J/psi measurements in an extended phase space towards
lower photon-proton centre of mass energies W_gammap. Differential cross
sections are presented as a function of t, the squared four-momentum
transfer at the proton vertex, and of W_gammap in the kinematical range
of low photon virtualities of Q^2 < 2.5 GeV^2. |
'