First observation of the hyper superheavy hydrogen 6ΛH

Three candidate events of the neutron-rich hypernucleus 6Λ H were uniquely identified in the FINUDA experiment at DANE, Frascati, by observing π + mesons from the (K − stop,π +) production reaction on 6Li targets, in coincidence with π − mesons from 6Λ H→6He+ π − weak decay. Details of the experiment and the analysis of its data are reported, leading to an estimate of (2.9 ± 2.0) · 10−6/K − stop for the 6Λ H production rate times the two-body π − weak decay branching ratio. The 6 ΛH binding energy with respect to 5H+Λwas determined jointly from production and decay to be BΛ = (4.0±1.1) MeV, assuming that 5H is unbound with respect to 3H+2n by 1.7 MeV. The binding energy determined from production is higher, in each one of the three events, than that determined from decay, with a difference of (0.98±0.74) MeV here assigned to the 0+ g.s. →1+ excitation. The consequences of this assignment to Λ hypernuclear dynamics are briefly discussed.