The first observation of the 6LH neutron-rich hypernucleus

The FINUDA experiment at DANE, Frascati, has observed the neutron-rich hypernucleus Λ6H by searching for (π+, π−) pairs in coincidence from the K− + 6Li → 6H + π+ production reaction and stop Λ the Λ6H → 6He + π− mesonic weak decay. The production rate of Λ6H undergoing this two-body de- cay has been found to be (2.9 ± 2.0) · 10−6/K− . The binding energy of 6H has been evaluated to be stop Λ BΛ(Λ6H) = (4.0 ± 1.1) MeV with respect to 5H + Λ, jointly from production and decay. A similar investigation has been carried out for the observation of the neutron-rich hypernucleus Λ9He by looking for the K− + 9Be → 9He + π+ reaction in coincidence with the 9He → 9Li + π− mesonic stop Λ Λ weak decay; an upper limit for the production rate of Λ9He undergoing the two-body decay has been found to be 4.2 · 10−6/K−stop (90% C.L.).