Exclusive ρ⁰ meson photoproduction with a leading neutron at HERA

Institute of Nuclear Physics Polish Academy of Sciences, Krakow, Poland

^* e-mail: lidia.goerlich@ifj.edu.pl

Published online: 29 November 2016

Abstract

A first measurement is presented of exclusive photoproduction of ρ⁰ 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 √s = 319 GeV and correspond to an integrated luminosity of 1.16pb⁻¹. The ρ⁰ 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. The phase space of the measurement is defined by the photon virtuality Q² < 2 GeV², the total energy of the photon-proton system 20 < W_γp < 100 GeV and the polar angle of the leading neutron θ_n < 0.75 mrad. The cross section of the reaction γp → ρ⁰nπ⁺ 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 ρ⁰ meson on the virtual pion. In the framework of one-pion-exchange dominance the elastic cross section of photon-pion scattering, σ^el(γπ⁺ → ρ°π⁺), is extracted. The value of this cross section indicates significant absorptive corrections for the exclusive reaction γp → ρ°nπ⁺.