Leading neutron energy and pT distributions in deep inelastic scattering and photoproduction at HERA

The production of energetic neutrons in ep collisions has been studied with the ZEUS detector at HERA. The neutron energy and p(T)(2) distributions were measured with a forward neutron calorimeter and tracker in a 40 pb(-1) sample of inclusive deep inelastic scattering (DIS) data and a 6 pb(-1) sample of photoproduction data. The neutron yield in photoproduction is suppressed relative to DIS for the lower neutron energies and the neutrons have a steeper p(T)(2)distribution, consistent with the expectation from absorption models. The distributions are compared to HERA measurements of leading protons. The neutron energy and transversemomentum distributions in DIS are compared to Monte Carlo simulations and to the predictions of particle exchange models. Models of pion exchange incorporating absorption and additional secondary meson exchanges give a good description of the data. (c) 2007 Elsevier B.V. All rights reserved.