Abstrakt
A first measurement is presented of exclusive photoproduction of rho(0) mesons associated with leading neutrons at HERA. The data were taken with the H1 detector in the years 2006 and 2007 at a centre-of-mass energy of root s = 319 GeV and correspond to an integrated luminosity of 1.16 pb(-1).
The rho(0) mesons with transverse momenta p(T) 0.35, are detected in the Forward Neutron Calorimeter. The phase space of the measurement is defined by the photon virtuality Q(2) rho(0)n pi(+) is measured as a function of several variables.
The data are interpreted in terms of a double peripheral process, involving pion exchange at the proton vertex followed by elastic photoproduction of a rho(0) meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, sigma(el)(gamma pi(+) -> rho(0)pi(+)), is extracted.
The value of this cross section indicates significant absorptive corrections for the exclusive reaction gamma p -> rho(0)n pi(+).