Measurement of the Doubly-Polarized $\vec{{^3}He}(\vec{\gamma},n)pp$ Reaction at 16.5 MeV and Its Implications for the GDH Sum Rule

TL;DR

This paper presents new measurements of the doubly-polarized photodisintegration of helium-3 at 16.5 MeV, comparing results with theoretical calculations and discussing implications for the GDH sum rule.

Contribution

It provides the first experimental data at 16.5 MeV and highlights discrepancies with existing three-body theoretical models, informing the understanding of the GDH sum rule.

Findings

Measured spin-dependent cross sections at 16.5 MeV

Observed the GDH integrand exceeds theoretical predictions

Identified limitations of current three-body calculations at higher energies

Abstract

We report new measurements of the doubly-polarized photodisintegration of $^3$He at an incident photon energy of 16.5 MeV, carried out at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility located at Triangle Universities Nuclear Laboratory (TUNL). The spin-dependent double-differential cross sections and the contribution from the three--body channel to the Gerasimov-Drell-Hearn (GDH) integrand were extracted and compared with the state-of-the-art three--body calculations. The calculations, which include the Coulomb interaction and are in good agreement with the results of previous measurements at 12.8 and 14.7 MeV, can no longer describe the cross section results at 16.5 MeV. The GDH integrand was found to be about one standard deviation larger than the maximum value predicted by the theories.