Pion structure function at small x from DIS data
  Production of leading neutrons in DIS is usually considered as a tool to measure the pion structure function at small x accessible at HERA. The main obstacle is the lack of reliable evaluations of the absorption corrections, which significantly suppress the cross section. We performed a parameter free calculation within the dipole approach and found the absorption corrections to be nearly as strong, as for neutron production in pp collisions. We also included the significant contribution of the iso-vector Reggeons with natural (\rho, a_2) and unnatural (a_1, \rho-\pi\ cut) parity with parameters constrained by phenomenology. With a certain modeling for the pion-to-proton ratio of the structure functions we reached good agreement with data from the ZEUS and H1 experiments, successfully reproducing the observed dependence on the fractional neutron momentum z, the photon virtuality Q^2, and the transverse momentum transfer q_T. 
B.Z. Kopeliovich, I.K. Potashnikova, B. Povh and Ivan Schmidt
hep-ph