The experimental data obtained from the reaction of 6 Li projectiles at 2A GeV on a fixed graphite target were analyzed to study the invariant mass distributions of d + π − and t + π − . Indications of a signal in the d + π − and t + π − invariant mass distributions were observed with significances of 5.3 σ and 5.0 σ , respectively, when including the production target, and 3.7 σ and 5.2 σ , respectively, when excluding the target. The estimated mean values of the invariant mass for d + π − and t + π − signal were 2059.3 ± 1.3 ± 1.7 MeV/c 2 and 2993.7 ± 1.3 ± 0.6 MeV/c 2 respectively. The lifetime estimation of the possible bound states yielding to d + π − and t + π − final states were deduced to be as 181 +30 −24 ± 25 ps and 190 +47 −35 ± 36 ps, respectively. Those final states may be interpreted as the two-body and three-body decay modes of a neutral bound state of two neutrons and a hyperon, 3 n.A hypernucleus, a subatomic system with at least one bound hyperon, is studied in order to deduce the information about fundamental hyperon (Y )-nucleon (N) and Y -Y interactions. Hypernuclei have been mainly studied by means of the missing-mass experiments with secondary-meson and primary-electron beams [1] and earlier with emulsion techniques and bubble chambers [2]. In these experiments, a variety of hypernuclei with the lightest hyperon, the hyperon, were produced and identified. However, the isospin of the produced hypernuclei is similar to that of the target nucleus in these experiments, since they are produced by the elementary process of converting one nucleon in the target nucleus into a hyperon.Information on the Λ-N interaction was already inferred from the hypernuclei in the vicinity of the β stability line * c.rappold@gsi.de † t.saito@gsi.de [3][4][5][6]. The nature of the Λ-N interaction for neutron-rich hypernuclei, in which the ΛN -ΣN coupling three-body force may play a role as described theoretically in Refs. [7-11], has not yet been studied in detail since only a few cases were observed, 10 Li [12], 7 He [13], and 6 H [14]. We thus search for other neutron-rich hypernuclei by means of induced reactions of heavy-ion beams.Neutron-and proton-rich hypernuclei can be indeed studied by using projectile fragmentation reactions of heavy-ion beams. In such reactions, a projectile fragment can capture a hyperon produced in the hot participant region to produce a hypernucleus [15][16][17][18][19]. They might also be produced in a multistage process, such as through a Fermi breakup decay of excited heavier hypernuclear spectators, possibly formed in peripheral collisions [19][20][21].We, the HypHI Collaboration, have proposed a series of experiments at the GSI Helmholtz Centre for Heavy Ion Research that would use induced reactions of stable heavy-ion beams and rare-isotope beams to produce 041001-1 0556-2813/2013/88(4)/041001 (6)