Neutron-rich hypernuclei: Evidence for 6λ H and search for9λ He

The FINUDA experiment at DAφNE, Frascati, has found evidence for the neutron-rich hypernucleus 6λ H studying (π+, π-) pairs in coincidence from the K -stop+6Li → 6λ H + π+-production reaction followed by 6λ H → 6He + 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-stop Its binding energy has been evaluated to be Bλ( 6λH) = (4.0 ± 1.1) MeV with respect to 5H + λ, jointly from production and decay. A systematic difference 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. A similar investigation has been carried out for the neutron-rich hypernucleus 9λHe studying the K -stop + 9Be → 9λ He + π+ reaction in coincidence with the 9λHe → 9Li + π- weak decay; an upper limit for the production rate of 9λHe undergoing the two-body π- decay has been found to be 4.2 ·10-6/K-stop(90% C.L.).