Parity-violating neutron spin rotation in hydrogen and deuterium

TL;DR

This paper calculates parity-violating neutron spin rotation angles in hydrogen and deuterium using effective field theory, aiming to constrain hadronic parity-violation parameters systematically.

Contribution

It provides a systematic EFT-based calculation of neutron spin rotation angles in hydrogen and deuterium, linking them to fundamental parity-violating parameters.

Findings

Expected signal size: 10^-7 to 10^-6 rad/m

No enhancement of nd observable over np

Results are properly renormalized with good convergence

Abstract

We calculate the (parity-violating) spin rotation angle of a polarized neutron beam through hydrogen and deuterium targets, using pionless effective field theory up to next-to-leading order. Our result is part of a program to obtain the five leading independent low-energy parameters that characterize hadronic parity-violation from few-body observables in one systematic and consistent framework. The two spin-rotation angles provide independent constraints on these parameters. Using naive dimensional analysis to estimate the typical size of the couplings, we expect the signal for standard target densities to be 10^-7 to 10^-6 rad/m for both hydrogen and deuterium targets. We find no indication that the nd observable is enhanced compared to the np one. All results are properly renormalized. An estimate of the numerical and systematic uncertainties of our calculations indicates excellent convergence. An appendix contains the relevant partial-wave projectors of the three-nucleon system.