pi-(4)He interactions at T=106 MeV

π - ⁴He interactions at T_π = 106 MeV have been studied by means of a self-shunted streamer chamber filled with helium at atmospheric pressure. This technique allowed reconstruction of the complete kinematics of the nuclear events under analysis, since tracks of slow p, α, tritium and ³He are readily measurable. The study revealed that the ⁴He nucleus behaves as a Planck radiator, emitting a T = 14 MeV Planck-like spectrum of high energy γs, when hit by a π beam of T_π = 106 MeV. A resonant behaviour in the π^- n invariant mass spectrum has been observed, with M π^- n = 1160 MeV and Γ = 20 MeV in the π^{- 4} He neutron knockout reaction: we consider this to be the first experimental evidence for the existence of the Δ^-. The observed mass shift and width narrowing are compatible with the activation of an isobaric collective resonance in the ⁴He nucleus. The collaboration has also observed a resonant behaviour in the π^-pp invariant mass spectrum in the π⁺ (¹⁰⁵Ag, ¹⁰³Ag) π^-pp double-charge-exchange reaction, on nuclear photoemulsion, compatible with the activation of the J^P = 0^- d^′ dibaryonic resonance with a strong p-p final state interaction. A new direct measured upper limit for the ν_μ mass has been derived by measuring a complete decay π - μ - e event recorded at the CERN PS179 experiment (over(p, ̄)²⁰Ne scattering): at a 90% confidence level, M μ_ν ≤ 2.2 MeV.