Observation of particle unstable 4H in pion absorption in 7Li

A particle unstable state of ⁴H has been identified in the reaction $\text{π}{}^{\mathrm{?}}\text{+}{}^7\text{Li}\text{→}{}^4\text{H+t}\text{,}{}^4\text{H}\text{→}\text{t}\text{+π}$ by observing the two emitted tritons. A resonance energy E_Γ=(2.7±0.6) MeV and a reduced width γ²=(2.3±0.6) MeV were deduced, in agreement with the parameters of the ground-state level (J^π=2^?) found in the p-wave of n-t-scattering. The yield per stopped pion is (5.6±1.8)×10^?4. Previous measurements in pion absorption are in disagreement with our results.