Measurement of leading neutron energy and transverse momentum distributions in deep inelastic scattering and photoproduction with ZEUS at HERA
              
The production of energetic neutrons in ep collisions was studied with the 
ZEUS detector at HERA. The neutron energy and transverse energy was measured 
with a forward neutron calorimeter and tracker. The inclusive deep inelastic 
scattering (DIS) data used correspond to an integrated luminosity of 40 pb-1 
and the photoproduction data to 6pb-1. The neutron yield in photoproduction 
is suppressed relative to DIS for the lower neutron energies and the neutrons 
have a steeper pT2  distribution, consistent with the expectation from 
absorption models. The distributions are compared to HERA measurements of 
leading protons. The neutron energy and transverse-momentum distributions 
in DIS are also compared to Monte Carlo simulations and to the predictions 
of particle exchange models. Models with pion exchange incorporating 
absorption and additional secondary meson exchanges give a good description 
of the data.