Abstract

In recent years, several experiments at the $e^-p$ collider HERA have collected high precision deep inelastic scattering (DIS) data on the spectrum of leading nucleon carrying a large fraction of the proton's energy. In this paper, we have analyzed recent experimental data on the production of forward proton and neutron in DIS at HERA in the framework of a perturbative QCD. We propose a technique based on the fractures functions framework, and extract the nucleon fracture functions (nucleon FFs) ${\cal M}_2^{(n/p)} (x, Q^2; x_L)$ from global QCD analysis of DIS data measured by ZEUS collaboration at HERA. We have shown that an approach based on the fracture functions formalism allows us phenomenologically parametrize the nucleon FFs. Considering both leading neutron as well as leading proton production data at HERA, we present the results for the separate parton distributions for all parton species, including valence quark densities, the anti-quark densities, the strange sea distribution, and the gluon distribution functions. We proposed several parameterizations for the nucleon FFs and open the possibility of these asymmetries. The obtained optimum set of nucleon FFs is accompanied by Hessian uncertainty sets which allow one to propagate uncertainties to other observables interest. The extracted results for the $t$-integrated leading neutron $F_2^{\rm LN(3)} (x, Q^2; x_L)$ and leading proton $F_2^{\rm LP(3)} (x, Q^2; x_L)$ structure functions are in good agreement with all data analyzed, for a wide range of fractional momentum variable $x$ as well as the longitudinal momentum fraction $x_L$.

Highlights

  • These days, a complete understanding of the nucleon and nuclear structures in terms of the underlying partonic and nucleonic constituents is one of the outstanding challenges in hadron physics

  • We have shown that the fracture functions approach, works well in describing the deep-inelastic leading nucleon (LN) data measured by the ZEUS Collaborations at HERA

  • We argued that the fracture functions could open some new possibilities for studying hadron structure and open a new window to predict a variety of hard processes at hadron colliders

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Summary

INTRODUCTION

These days, a complete understanding of the nucleon and nuclear structures in terms of the underlying partonic and nucleonic constituents is one of the outstanding challenges in hadron physics. The H1 and ZEUS experiments at HERA have studied the production of forward protons, neutrons, and photons which carry a large fraction of the longitudinal momentum of the incoming proton [53,54,55,56,62,63,64,65] These analyses have demonstrated that models of DIS are able to reproduce the forward nucleons’ measurements if contributions from different production mechanisms are considered, such as one pion exchange (OPE) [56], diffractive dissociation, elastic scattering of the proton [56,64] as well as the fracture functions (FFs) formalism [66]. V, we summarize our findings and preview future extensions of the present analysis

THEORY SETUP
The fracture functions
Leading nucleon structure functions and observables
Evolution of the nucleon FFs
OUTLINE OF THE ANALYSIS
Input parametrizations
Selection of data sets
ZEUS-02 data on leading neutron production
ZEUS-06 data on leading proton production
ZEUS-09 data on leading proton production
THE RESULTS OF GLOBAL QCD ANALYSIS
SUMMARY AND CONCLUSIONS

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