New Neutron Polarizabilities from Deuterium Compton Scattering at HI$\gamma$S

Abstract

Elastic and inelastic Compton-scattering cross sections of the deuteron were measured at HI$\gamma$S using a circularly polarized, quasi-monoenergetic $\gamma$-ray beam (61.0 MeV). Scattered $\gamma$ rays from a liquid deuterium target were detected at $55^{\circ }$, $115^{\circ }$, and $150^{\circ }$. High-resolution NaI(Tl) detectors at backward angles enabled separation of elastic and inelastic events. A $\chi$EFT analysis of the data yields new neutron scalar polarizabilities, ${\alpha }_{E1}^n=12.25\pm 1.1(\mathrm{stat})\pm 0.3(\mathrm{BSR})\pm 0.8(\mathrm{th})$ and ${\beta }_{M1}^n=2.95\mp 1.1(\mathrm{stat})\mp 0.3(\mathrm{BSR})\mp 0.8(\mathrm{th})$ (in units of $10^{-4}{\mathrm{fm}}^3$) reducing statistical uncertainties by 12 %.