Pion absorption from the lowest atomic orbital in 2H, 3H and 3He

TL;DR

This study calculates pion absorption rates in light nuclei using chiral effective field theory, highlighting the importance of two-body operators and final state interactions, and compares results with experimental data.

Contribution

It provides a comprehensive calculation of pion absorption rates in 2H, 3H, and 3He including full final state interactions and chiral EFT operators, offering improved theoretical insights.

Findings

Absorption rates depend strongly on the pion absorption operator used.

Two-nucleon forces significantly influence the final state interactions.

Calculated rates for pi- + 2H agree well with experimental data.

Abstract

The pi- + 2H -> n + n, pi- + 3H -> n + n + n, pi- + 3He -> n + d and pi- + 3He -> p + n + n capture reactions from the lowest atomic orbitals are studied under full inclusion of final state interactions. Our results are obtained with the single-nucleon and two-nucleon transition operators derived at leading order in chiral effective field theory. The initial and final three-nucleon states are calculated with the chiral nucleon-nucleon SMS potential up to N4LO+ augmented by the consistently regularized chiral N2LO three-nucleon potential. We found that absorption rates depend strongly on the nuclear pion absorption operator used, and its two-body parts change the rates by a few orders of magnitude. The final state interactions between nucleons generated by the two-nucleon forces are also important, while the three-nucleon interaction plays a visible role only in the pi- + 3He -> n + d reaction. Our absorption rate for the pi- + 2H -> n + n process is in good agreement with the experimental data from the hadronic ground-state broadening in pionic deuterium. The capture rates on 3He are also generally consistent with the spectroscopic data within error bars, though our central values are found to be systematically below the data. We show that for the three-body breakup processes the dominant contributions to the absorption rates arise from the quasi-free scattering and final-state interaction kinematical configurations.