A. Bezaguet

Heavy liquid chamber analysis of ηO → 3π and ηO → γγ decay-modes

Abstract From 199 η O → 3 π O → 6 γ , 526 η O → π + π − π O and 401 η O → γγ events with all γ-rays reconstructed in a heavy liquid bubble chamber, we obtain direct and independent measurements of the branching ratios: R 1 = Γ ( η O → 3 π O )/ Γ ( η O → π + π - π O ) = 1.50 -0.29 +0.15 and R 2 = Γ ( η O → γγ )/ Γ ( η O → π + π - π O ) = 1.72 ± 0.25. We also study the Dalitz-plots for the modes η O → 3π O and η O → π + π - π O , and find no significant variation of the amplitude of the decay η O → 3 π O .

Search for the decay mode ηO → πOγγ

Abstract A study of 4γ events has been made in the production reaction π + p → π + p + 4γ using a hydrogen target inside a heavy liquid bubble chamber. The analysis shows no evidence for the decay mode η O → π O γγ. With 90% of confidence, we find (η O → π O γγ)/(η O → all modes)

Direct search for the C-violating decay η0 → π0 e+ e-

Abstract No examples of this decay have been found in a sample of film containing 387 η 0 → π 0 π + π - decays with π 0 detected. The film was taken with the Ecole Polytechnique heavy liquid bubble chamber exposed to 950 MeV/ c π - at Saclay. With 90% confidence the branching ratio η 0 → π 0 e + e - is less than 0.23% of all η 0 decays.

Heavy liquid bubble chamber analysis of η0 neutral decay modes: ηo → 3π0 and η0 → γγ

Abstract The following decays of η0 mesons produced in 350 000 photographs of a heavy liquid bubble chamber have been observed: η0 → π+π−π0, η0 → 3π0 → 6γ, η0 → γγ. All the γ-rays coming from these decays have been observed and measured; this provides a direct separation of the two neutral modes and independent measurements of the two following branching ratios: R1 = Γ (η0 → 3π0)/Γ(η0 → π+π−π0 and R2 = Γ(gh0 → γγ)/Γ(η0 → π+π−π0). This analysis has been done with 526 η0 → π+π−π0(π0 → γγ), 199 η0 → 3π0 → 6γ and 401 η0 → γγ events. The result R 1 = 1.50 −0.29 +0.15 is in agreement with the theoretical predictions assuming that η0 → 3π decays are pure ΔI = 1 transitions. The result R2 = 1.72 ± 0.25, combined with with R1 and compared with the present world average of the ratio Γ(η0 → neutrals)/gG(η0 → π+π−π0) is compatible with the absence of the mode η0 → π0γγ or with only a small decay rate for this last mode. Then η0 → 3π0 Dalitz plot has been studied, the three π0 being reconstructed from the measurements of the 6γ-rays, using kinematical fits. No significant variation of the η0 → 3π0 amplitude has been found. The coefficient of the term quadratic in pion energies in this amplitude is found to be α = −0.32 ± 0.37.

Further results in direct search for C violating decay mode η0 → π0e+e−

No example of this decay has been found in a sample of film containing 752 η0 → π0π+π− with π0 detected. The pictures were taken with the Ecole Polytechnique heavy liquid bubble chamber exposed to a 950 MeVc π− beam at Saclay. With 90% of confidence the decay fraction is less than 0.9 × 10−3 of all η0 decays.

Direct evidence for the decay mode ωo → πoγ

Abstract A study of neutral decay modes of ω o is performed using the production reaction π + + p → π + + p + ω o . The directions and momenta of charged tracks and gamma rays are measured. The results give direct evidence for the decay of ω o into πγ.

Direct search for the decay mode η → π+π−π0γ

Abstract A systematic search for the decay mode η 0 → π + π − π 0 γ has been made with direct detection of the two charged pions and of the three γ -rays in the Ecole Polytechnique heavy liquid bubble chamber. The branching ratio R = Γ ( η 0 → π + π − π 0 γ )/ Γ ( η 0 → π + π − π 0 ) is found to have an upper limit of 1.7% with 90% confidence level.