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

TL;DR

This study measures the energy and transverse momentum distributions of leading neutrons in electron-proton collisions at HERA, comparing results with models and proton data to understand neutron production mechanisms.

Contribution

It provides detailed measurements of neutron energy and pT distributions in DIS and photoproduction, and evaluates the effectiveness of particle exchange models including absorption effects.

Findings

Neutron yield is suppressed in photoproduction compared to DIS.

Neutrons have a steeper pT^2 distribution in photoproduction.

Particle exchange models with absorption fit the data well.

Abstract

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 transverse-momentum 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.