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

pi-He-4 interactions at T-pi = 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, alpha, tritium and He-3 are readily measurable. The study revealed that the He-4 nucleus behaves as a Planck radiator, emitting a T = 14 MeV Planck-like spectrum of high energy gamma s, when hit by a pi beam of T-pi = 106 MeV. A resonant behaviour in the pi(-)n invariant mass spectrum has been observed, with M pi(-)n = 1160 MeV and Gamma = 20 MeV in the pi He-4 neutron knockout reaction: we consider this to be the first experimental evidence for the existence of the Delta(-). 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 pi(-)pp invariant mass spectrum in the pi(+)(Ag-105, Ag-103)pi(-)pp double-charge-exchange reaction, on nuclear photoemulsion, compatible with the activation of the J(P) = 0(-)d(1) dibaryonic resonance with a strong p-p final state interaction. A new direct measured upper limit for the v(mu) mass has been derived by measuring a complete decay pi-mu-e event recorded at the CERN PS179 experiment (p(20)Ne scattering): at a 90% confidence level, M mu(v) <= 2.2 MeV.