Neutron-rich Λ-Hypernuclei study with the FINUDA experiment

The FINUDA experiment at DAΦNE, Frascati, has found evidence for the neutron-rich hypernucleus 6 H studying (π+, π−) pairs in coincidence from the K− + Λ stop 6 Li → 6Λ H + π+ production reaction followed by 6Λ H → 6 He + π− weak decay. The production rate of 6ΛH undergoing this two-body π− decay has been found to be (2.9 ± 2.0) · 10−6/K− . Its binding energy has been evaluated to be B (6 H) = (4.0 ± 1.1) stop ΛΛ MeV with respect to (5H + Λ), jointly from production and decay. A systematic differ- ence of (0.98 ± 0.74) MeV between BΛ values derived separately from decay and from production has been tentatively assigned to the 6ΛH 0+g.s. → 1+ excitation. 9 A similar investigation has been carried out for the neutron-rich hypernucleus ΛHe study- ingtheK− +9Be→9He+π+ reactionincoincidencewiththe9He→9Li+π− weak stop Λ 9 Λ − decay; an upper limit for the production rate of ΛHe undergoing the two-body π decay has been found to be 4.2 ·10−6/K−stop (90% C.L.).