Speaker
Dr.
Ewald Paul
(physikalisches Insitut bonn)
Description
The exclusive reaction gamma p -> psi(2S) p has been studied in both
deep inelastic electroproduction and in photoproduction with the ZEUS
detector in ep collisions at HERA using an integrated luminosity of
350 pb-1. The psi(2S) mesons were identified via their decay chain:
psi(2S) -> J/psi pi+ pi- with J/psi -> mu+ mu-. The ratio of the
production cross sections R = sigma(psi(2S)) / sigma(J/psi) was measured
as a function of the kinematic variables, in particular the photon-proton
centre-of-mass energy, W, and compared to predictions of perturbative QCD.
The exclusive production of dijets in diffractive deep inelastic lepton-proton
scattering has also been measured. Jets have been reconstructed in the
photon-Pomeron (gamma*-IP ) centre-of-mass system frame using the exclusive
k_T algorithm. The cross section for the exclusive production of
dijets is given as a function of the angle between the plane defined by exchanged
photon and dijet system and the plane defined by the incoming and scattered lepton
momenta in the \gamma*-IP rest frame. It is compared to theoretical predictions
of models based on boson-gluon fusion and two-gluon exchange processes.
The first measurement of exclusive photoproduction of rho mesons associated
with leading neutrons with the H1 detector at HERA is also presented. The data
correspond to an integrated luminosity of 1.12 pb-1. The rho meson is identified
by its decay pions reconstructed in the central tracking chamber, while the
leading neutron carrying a large fraction of the incoming proton momentum,
x_L>0.3, is detected in the Forward Neutron Calorimeter. The cross section
of the reaction gamma+p -> rho+n+Y, where Y is a small mass system escaping
undetected in the proton direction, is measured as a function of the neutron
energy, the invariant mass of the pi+ pi- system and p_T^2 of the rho meson.
The data are interpreted in terms of two dominant contributions: diffractive
proton dissociation channel and elastic production via virtual pion exchange.
Primary authors
Karin Daum
(DESY)
Stefan Schmitt
(DESY)
