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

Abstract

The FINUDA experiment at DAΦNE, Frascati, has found evidence for the neutron-rich hypernucleus 6ΛH studying (π+, π−) pairs in coincidence from the K−stop+6Li → 6ΛH+π+ production reaction followed by 6ΛH → 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 → 9ΛHe + 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.).