$\Lambda$ separation energy of the hypertriton
In plain words
The hypertriton, a $\Lambda$ hyperon bound to a deuteron, is the lightest hypernucleus and the anchor of fits to hyperon-nucleon forces. Measurements of how strongly the $\Lambda$ is held differ by a factor of about four.
Precise statement
Determine $B_{\Lambda}(3_{\Lambda} H)=M(d)+M(\Lambda)-M(3_{\Lambda} H)$. Emulsion data give $0.13 \pm 0.05\ \mathrm{MeV}$, STAR gives $0.41 \pm 0.12\ (\mathrm{stat}) \pm 0.11\ (\mathrm{syst})\ \mathrm{MeV}$ (Nature Physics 16, 409, 2020), and ALICE gives $0.102 \pm 0.063\ (\mathrm{stat}) \pm 0.067\ (\mathrm{syst})\ \mathrm{MeV}$ (PRL 131, 102302, 2023). Answer: $B_{\Lambda}$ with uncertainty below $20\ \mathrm{keV}$ and the resulting constraint on the spin-singlet $\Lambda N$ interaction and the $\Lambda NN$ force.
What would settle it
Decay-pion spectroscopy of $3_{\Lambda} H$ with absolute mass calibration below 20 keV, cross-checked by high-statistics invariant-mass measurements at the LHC.
Status in the literature
Unverified note
The 2023 ALICE value, together with its measured lifetime of $253 \pm 11\,(\mathrm{stat}) \pm 6\,(\mathrm{syst})\,\mathrm{ps}$ close to the free $\Lambda$ value, favors weak binding, about 1.7 standard deviations from STAR; STAR deuteron-$\Lambda$ correlations (arXiv 2511.15493, 2025) opened an independent route.