Measurement of leading proton and neutron production in deep-inelastic scattering at HERA

Deep-inelastic scattering events with a leading baryon have been detected by the I-IL experiment at HERA using a forward proton spectrometer and a forward neutron calorimeter. Semi-inclusive cross sections have been measured in the kinematic region 2 less than or equal to Q(2) less than or equal to 50GeV(2), 6 x 10(-5) less than or equal to x less than or equal to 6 x 10(-3) and baryon p(T) less than or equal to 200 MeV, for events with a final-state proton with energy 580 less than or equal to E' less than or equal to 740 GeV, or a neutron with energy E' greater than or equal to 160 GeV. The measurements are used to test production models and factorization hypotheses. A Regge model of leading baryon production which consists of pion, pomeron and secondary reggeon exchanges gives an acceptable description of both semi-inclusive cross sections in the region 0.7 less than or equal to E'/E-p less than or equal to 0.9, where E-p is the proton beam energy. The leading neutron data are used to estimate for the first time the structure function of the pion at small Bjorken-x.