Charge-symmetry breaking in the mass-4 mirror hypernuclei

Define $\Delta B_{\Lambda}(J) = B_{\Lambda}(4_{\Lambda}\,\mathrm{He}) - B_{\Lambda}(4_{\Lambda}\,\mathrm{H})$ for the $0+$ ground and $1+$ excited states. STAR measured $\Delta B_{\Lambda}(0+) = 0.16 \pm 0.14\,(\mathrm{stat}) \pm 0.10\,(\mathrm{syst})\,\mathrm{MeV}$ and $\Delta B_{\Lambda}(1+) = -0.16 \pm 0.14\,(\mathrm{stat}) \pm 0.10\,(\mathrm{syst})\,\mathrm{MeV}$ (PLB 834, 137449, 2022). Determine the mechanism ($\Lambda-\Sigma0$ mixing, $\Lambda N$ to $\Sigma N$ conversion with one-pion exchange, charge-symmetry-breaking contact terms) and the implied difference between the $\Lambda p$ and $\Lambda n$ scattering lengths. Answer: an ab initio four-body calculation with a chiral YN interaction reproducing both values, with a prediction of the $\Lambda n$ scattering length.

Gamma-ray and decay-pion spectroscopy of both hypernuclei at the $20\,\mathrm{keV}$ level, combined with four-body calculations using chiral YN forces at next-to-next-to-leading order.