Spin Polarization in $\gamma d \to \vec{n}p$ at Low Energies with a Pionless Effective Field Theory

TL;DR

This paper uses pionless effective field theory to calculate neutron polarization and cross sections in deuteron photodisintegration at low energies, finding good agreement for cross sections but notable discrepancies in polarization predictions.

Contribution

It applies pionless EFT with dibaryon fields to analyze neutron polarization in gamma-deuteron reactions at low energies, highlighting areas needing further investigation.

Findings

Total and differential cross sections agree with experimental data.

Neutron polarization results significantly differ from experimental measurements.

Provides insights into the limitations of current EFT models for polarization.

Abstract

With the use of pionless effective field theory including dibaryon fields, we study the $\gamma d \to \vec{n} p$ reaction for the laboratory photon energy $E_\gamma^{lab}$ ranging from threshold to 30 MeV. Our main goal is to calculate the neutron polarization $P_{y'}$ defined as $P_{y'} = (\sigma_+ - \sigma_-)/(\sigma_+ + \sigma_-)$, where $\sigma_+$ and $\sigma_-$ are the differential cross sections for the spin-up and spin-down neutrons, respectively, along the axis perpendicular to the reaction plane. We also calculate the total cross section as well as the differential cross section $\sigma(\theta)$, where $\theta$ is the colatitude angle. Although the results for the total and differential cross sections are found to agree reasonably well with the data, the results for $P_{y'}$ show significant discrepancy with the experiment. We comment on this discrepancy.