Neutron spin structure from polarized deuteron DIS with proton tagging

W Cosyn,C Weiss

doi:10.1016/j.physletb.2019.135035

Abstract

Polarized electron-deuteron deep-inelastic scattering (DIS) with detection of the spectator proton (“tagged DIS”) enables measurements of neutron spin structure with maximal control of nuclear effects. We calculate the longitudinal spin asymmetries in polarized tagged DIS using methods of light-front nuclear structure and study their dependence on the measured proton momentum. Asymmetries can be formed with all three deuteron spin states (±1,0) or the two maximum-spin states only (±1, involving tensor polarization). The proton momentum dependence can be used to select pure S-wave configurations in the deuteron and eliminate D-wave depolarization (transverse momenta ppT≲ 100 MeV). Free neutron spin structure can be extracted model-independently through pole extrapolation of the tagged asymmetries. Such measurements could be performed at a future electron-ion collider (EIC) with polarized deuteron beams and forward proton detectors.

Highlights

Nucleon spin structure studies require measurements of polarized deep-inelastic lepton scattering (DIS) on both the proton and the neutron; see Refs. [1,2,3] for a review
The neutron spin structure functions are extracted from DIS measurements on polarized light nuclei
Collider (EIC) [12,13], it is necessary to consider new types of measurements that reduce the theoretical uncertainty in neutron spin structure extraction

Summary

Introduction

Nucleon spin structure studies require measurements of polarized deep-inelastic lepton scattering (DIS) on both the proton and the neutron; see Refs. [1,2,3] for a review. The neutron spin structure functions are extracted from DIS measurements on polarized light nuclei (deuteron 2H ≡ D, 3He). Extrapolation of the measured proton momentum dependence to the on-shell point eliminates nuclear initial-state modifications and final-state interactions and permits the extraction of free neutron structure [15]. With the possibility of polarized deuteron beams at EIC, it is interesting to assess the potential of polarized tagged DIS for precise measurements of neutron spin structure. In this letter we report about the development of a theoretical framework for neutron spin structure measurements with polarized tagged DIS in collider experiments; see Ref. Using methods of light-front (LF) nuclear structure, we calculate the longitudinal spin asymmetries in polarized tagged DIS and study the dependence on the measured proton momentum. Details will be provided in a forthcoming article [23]

Spin asymmetries in polarized tagged DIS

Deuteron light-front wave function

Deuteron light-front spectral function

Deuteron structure in spin asymmetries

Neutron spin structure from pole extrapolation

Conclusions and extensions