ATLAS

Abstract:

The production of energetic neutrons in ep collisions has been studied with the ZEUS detector at HERA. The neutron energy and pT² 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 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 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. © 2007 Elsevier B.V. All rights reserved.

Abstract:

Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 82 pb^−1. Charm has been tagged by reconstructing D∗+, D0, D+ and D+s (+ c.c.) charm mesons. The charm hadrons were measured in the kinematic range pT(D∗+, D0, D+) > 3 GeV, pT(D+s) > 2 GeV and |η(D)| < 1.6 for 1.5 < Q2 < 1000 GeV^2 and 0.02 < y < 0.7. The production cross sections were used to extract charm fragmentation ratios and the fraction of c quarks hadronising into a particular charm meson in the kinematic range considered. The cross sections were compared to the predictions of next-to-leading-order QCD, and extrapolated to the full kinematic region in pT (D) and η(D) in order to determine the open-charm contribution, Fc¯ c2 (x, Q^2), to the proton structure function F2.