Premiere observation de la production de π⁰ dans la reaction d+d→α+π⁰ interdite par la conservation de la symetrie de charge et mesure de la reaction d+d→α+γ

Abstract

The reaction d+d→α+π⁰ which is in clear violation of charge symmetry conservation, has been observed for the first time at a laboratory energy of 1.10 GeV in an experiment carried out at the Saturne synchroton at Saclay. The number of π⁰'s detected corresponds to a differential cross section $\text{d}\text{σ}\text{d}\text{Ω}{}^{\mathrm{\ast }}\text{(π}{}^0\text{)}\text{= 0.97 ± 0.20 ± 0.15}\text{pb/sr}$ at a centre-of-mass angle of θ_c.m. = 107°, where the first error bar refers to the statistical uncertainty and the second to the systematic. The reaction d+d→α+γ was measured simultaneously with the π⁰ production, leading to a differential cross section of $\text{d}\text{σ}\text{d}\text{Ω}{}^{\mathrm{\ast }}\text{(γ)}\text{= 0.82±0.18±0.10}\text{pb/sr}$ at the slightly larger angle of θ_c.m. = 110°. The available predictions of theoretical models of charge symmetry breaking, based upon η/π mixing, fall an order of magnitude below our measurement. However, these predictions for the η/π mixing level might be boosted by the η threshold (1.121 GeV) proximity, where this experiment is performed.