The authors respond to a recent suggestion that a sharp peak in pion momentum seen in a Mainz Microtron (MAMI) experiment might come from the decay of the hypernucleus 7ΛHe instead of the hypertriton (written 3ΛH). They present quantitative tests of that idea and conclude that the original assignment to the hypertriton remains the most supported interpretation of their data.

A key test was a search for a companion decay line that the 7ΛHe explanation would predict. If the 113.8 MeV/c pion line were coming from 7ΛHe decays to an excited state of 7Li, then a stronger companion line should appear near 114.5 MeV/c. The MAMI group fitted the pion-momentum spectrum with a signal-plus-background model and found no statistically significant excess at 114.5 MeV/c. They set an upper limit of 8.7 events at 90% confidence near that position, while the observed 113.8 MeV/c peak had a fitted yield of 17.8 events within the same window.

Using the intensity ratio predicted by the alternative interpretation (about 2:1 in favor of the companion line), the 7ΛHe hypothesis would predict roughly 36 events at 114.5 MeV/c. That expectation is more than four times the observed upper limit. Turning the argument around, the upper limit implies that at most about 4.4 of the 17.8 observed events at 113.8 MeV/c could come from 7ΛHe. In other words, even under favorable assumptions the 7ΛHe contribution could explain only about 25% of the signal, leaving the majority unexplained by that hypothesis.

The authors give a second reason to doubt the 7ΛHe assignment. That interpretation requires a Lambda (Λ) binding energy for 7ΛHe of 5.84±0.07 MeV. A direct spectroscopic measurement by the JLab HKS experiment found BΛ(7ΛHe)=5.55±0.10(stat)±0.11(syst) MeV. Accepting the 7ΛHe explanation would require the JLab value to be in error by roughly two standard deviations without any experimental reason for such a discrepancy. The MAMI team therefore regards the JLab result as a more reliable constraint on the 7ΛHe binding energy.