Evidence for heavy hyperhydrogen HΛ6

Evidence for the neutron-rich hypernucleus HΛ6 is presented from the FINUDA experiment at DAΦNE, Frascati, studying (π +,π -) pairs in coincidence from the Kstop- +Li6→HΛ6+π + production reaction followed by HΛ6→He6+π - weak decay. The production rate of HΛ6 undergoing this two-body π - decay is determined to be (2.9±2.0)×10 -6/Kstop-. Its binding energy, evaluated jointly from production and decay, is B Λ(HΛ6)=(4. 0±1.1)MeV with respect to H5+Λ. A systematic difference of (0.98±0.74)MeV between B Λ values derived separately from decay and from production is tentatively assigned to the HΛ6 0g.s.+→1 + excitation. © 2012 American Physical Society.