π-⁴He interactions at T=106 MeV

View the MathML sourceπ–He4 interactions at View the MathML sourceTπ=106MeV 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 pp, αα, tritium and 3He are readily measurable. The study revealed that the 4He nucleus behaves as a Planck radiator, emitting a View the MathML sourceT=14MeV Planck-like spectrum of high energy γγs, when hit by a ππ beam of View the MathML sourceTπ=106MeV. A resonant behaviour in the π−nπ−n invariant mass spectrum has been observed, with View the MathML sourceMπ−n=1160MeV and View the MathML sourceΓ=20MeV in the View the MathML sourceπ−4He neutron knockout reaction: we consider this to be the first experimental evidence for the existence of the Δ−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−π−pp invariant mass spectrum in the View the MathML sourceπ+(Ag105,Ag103)π−pp double-charge-exchange reaction, on nuclear photoemulsion, compatible with the activation of the JP=0−d′JP=0−d′ dibaryonic resonance with a strong p–p final state interaction. A new direct measured upper limit for the νμνμ mass has been derived by measuring a complete decay π–μ–eπ–μ–e event recorded at the CERN PS179 experiment (View the MathML sourcep̄20Ne scattering): at a 90% confidence level, View the MathML sourceMμν≤2.2MeV.