Abstract
TheWASA-at-COSY experiment is, besides meson production processes, dedicated to studies on rare and forbidden decays of light mesons. In extensive η -production beam times, a high-statistics data set have been collected by means of proton-proton scattering which opens the door to studies on forbidden decays like the C -parity violating process η → π 0 e + e − . In this article, an optimized detector calibration leading to a significantly improved missing mass resolution and a preliminary decay analysis are presented.
Highlights
Investigations on fundamental symmetries like the C-parity are a main tool for testing standard model predictions
The final state can be achieved by higher order processes fulfilling all conservation laws but these highly suppressed, i.e., a relative branching ratio in the order of 10−12 to 10−9 is expected by calculations
The data set is analyzed in order to observe the decay η → π0e+e− or, at least, to improve the existing upper limit for the relative branching ration
Summary
Investigations on fundamental symmetries like the C-parity are a main tool for testing standard model predictions. The final state can be achieved by higher order processes fulfilling all conservation laws but these highly suppressed, i.e., a relative branching ratio in the order of 10−12 to 10−9 is expected by calculations This decay of the η-meson is a perfect probe for testing the C-parity conservation within the standard model up to a relative branching ratio of ≈10−9 and may give access to physics beyond the standard model by assuming a dark Z-like U-boson as an intermediate state [1]. Up to now, this decay has not been observed and only an upper limit for the branching ratio of 4 × 10−5 is quoted by the PDG [2]. This article presents results obtained with the latter data set
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