Neutron-rich hypernuclei: evidence for 6ΛH and search for 9ΛHe

The FINUDA experiment at DA Φ NE, Frascati, has found evidence for the neutron-rich hypernucleus6 Λ H studying ( π + , π − ) pairs in coincidence from the K − stop + 6 Li → 6 Λ H+π + production reaction followed by 6 Λ H → 6 He + π − weak decay. The production rate of 6 Λ H undergoing this two-body π − decay has been found to be (2.9 ± 2.0) · 10 −6 / K − stop .Its binding energy has been evaluated to be B Λ ( 6 Λ H) = (4.0 ± 1.1) MeV with respect to 5 H + Λ , jointly from production and decay. A systematic difference of (0.98 ± 0.74) MeV between B Λ values derived separately from decay and from production has been tentatively assigned to the 6 Λ H 0 + g.s. → 1 + excitation.A similar investigation has been carried out for the neutron-rich hypernucleus9 Λ He studying the K − stop + 9 Be → 9 Λ He + π + reaction in coincidence with the 9 Λ He → 9 Li + π − weak decay; an upper limit for the production rate of 9 Λ He undergoing the two-body π − decay has been found to be 4.2 · 10 −6 /K − stop (90% C.L.).