Exclusive ${\rho }^0$ Meson Photoproduction with a Leading Neutron at HERA

Abstract

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 319 GeV and correspond to an integrated luminosity of 1.16/pb. The ${\rho }^0$ mesons with transverse momenta $p_T<1$ GeV are reconstructed from their decays to charged pions, while leading neutrons carrying a large fraction of the incoming proton momentum, $x_L>$0.35, are detected in the Forward Neutron Calorimeter having a polar angular acceptance < 0.75 mrad. Single- and double-differential cross sections are 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 is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction $\gamma p\to {\rho }^{0}n{\pi }^{+}$.

Comments: LaTeX2e, 7 pages with 6 figures. Contribution to the DIS-2016 workshop, to be published in the proceedings