Pion absorption from the lowest atomic orbital in H2, H3 , and

J. Golak, V. Urbanevych,R. Skibiński,H. Witała, K. Topolnicki,V. Baru, A. A. Filin, E. Epelbaum, H. Kamada, A. Nogga

The ${\ensuremath{\pi}}^{\ensuremath{-}}+^{2}\mathrm{H}\ensuremath{\rightarrow}n+n, {\ensuremath{\pi}}^{\ensuremath{-}}+^{3}\mathrm{H}\ensuremath{\rightarrow}n+n+n, {\ensuremath{\pi}}^{\ensuremath{-}}+^{3}\mathrm{He}\ensuremath{\rightarrow}n+d$, and ${\ensuremath{\pi}}^{\ensuremath{-}}+^{3}\mathrm{He}\ensuremath{\rightarrow}p+n+n$ capture reactions from the lowest $1S$ 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 semilocal momentum space potential up to ${\mathrm{N}}^{4}{\mathrm{LO}}^{+}$, augmented by the consistently regularized chiral ${\mathrm{N}}^{2}\mathrm{LO}$ 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 ${\ensuremath{\pi}}^{\ensuremath{-}}+^{3}\mathrm{He}\ensuremath{\rightarrow}n+d$ reaction. Our absorption rate for the ${\ensuremath{\pi}}^{\ensuremath{-}}+^{2}\mathrm{H}\ensuremath{\rightarrow}n+n$ process is in good agreement with the experimental data from the hadronic ground-state broadening in pionic deuterium. The capture rates on $^{3}\mathrm{He}$ 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.