Evidence for kaon-bound state K-pp produced in K- absorption reactions at rest

We have searched for a deeply bound kaonic state by using the FINUDA spectrometer installed at the e+e- collider DAFNE. Almost monochromatic K-’s produced through the decay of Phi(1020) mesons are used to observe K- absorption reactions stopped on very thin nuclear targets. Taking this unique advantage, we have succeeded to detect a kaon-bound state K-pp through its two-body decay into a Lambda hyperon and a proton. The binding energy and the decay width are determined from the invariant-mass
distribution as 115 +/- 6 (stat) +/- 3 (syst) MeV and 67 +/- 14 (stat) +/- 2 (syst) MeV, respectively.