Pion structure function at smallxfrom deep-inelastic scattering data

Abstract

The production of leading neutrons in deep-inelastic scattering 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 isovector Reggeons with natural ($\ensuremath{\rho}$, ${a}_{2}$) and unnatural (${a}_{1}$, $\ensuremath{\rho}\mathrm{\text{\ensuremath{-}}}\ensuremath{\pi}$ 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 dependences on the fractional neutron momentum $z$, the photon virtuality ${Q}^{2}$, and the transverse momentum transfer ${q}_{T}$.