Pion structure function at small x from DIS data

TL;DR

This paper presents a parameter-free dipole approach calculation of the pion structure function at small x using DIS data, accounting for absorption corrections and Reggeon contributions, achieving good agreement with experimental results.

Contribution

It introduces a reliable, parameter-free dipole model calculation of absorption corrections and Reggeon effects in leading neutron production in DIS, improving the extraction of the pion structure function.

Findings

Absorption corrections are as strong as in pp collisions.

Reggeon contributions significantly affect the results.

Model reproduces ZEUS and H1 data well.

Abstract

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.