# Longitudinal spin asymmetries in polarized deuteron DIS with spectator tagging

## TL;DR

This paper explores how polarized electron-deuteron deep-inelastic scattering with spectator proton tagging can precisely measure neutron spin structure functions, accounting for nuclear effects using light-front nuclear structure methods, and proposes feasible experimental setups at future colliders.

## Contribution

It introduces a novel approach to extract neutron spin structure functions using spectator tagging and analyzes the associated nuclear structure factors with light-front methods.

## Key findings

- Two-state deuteron spin asymmetry allows accurate extraction of $g_{1n}$.
- Measurement feasibility at future electron-ion colliders is demonstrated.
- Nuclear effects can be controlled with spectator proton tagging.

## Abstract

Polarized electron-deuteron DIS with spectator proton tagging offers a way of measuring the neutron spin structure functions with maximal theoretical control of nuclear effects. We calculate the nuclear structure factors in the longitudinal double-spin asymmetries using methods of light-front nuclear structure. A unique feature of the spin-1 system is that spin asymmetries can be formed either relative to the cross section in all three spin states ($\lambda_d = \pm 1, 0$) or in the two maximum-spin states only ($\pm 1$, involving tensor polarization). We find that the two-state deuteron spin asymmetry at small spectator proton momenta permits accurate extraction of the neutron structure function $g_{1n}$. Such measurements could be performed at a future electron-ion collider (EIC) with polarized deuteron beams and suitable forward detectors.