Recent Results on Meson Decays from A2

Abstract

Light meson decays are used to investigate topics related to fundamental aspects of particle physics. Precision measurements of meson Dalitz decays give input to theoretical evaluations of the Hadronic Light-by-Light contribution (HLbL) to the anomalous magnetic moment of the muon. The pseudoscalar η' decays allow for studies of topics like ππ scattering lengths, effective field theories and fundamental symmetries. The A2 collaboration, using the Crystal Ball/TAPS setup at MAMI, has recently published several high precision results on transition form factors which are related to HLbL. The value obtained for the slope parameter of the π0 electromagnetic (e/m) transition form factor (TFF) is απ = 0.030 ± 0.010tot. The slope parameters for the e/m TFFs of ηγ and ωπ0 are [see formula in PDF] and [see formula in PDF], respectively. In 2014 the collaboration had a dedicated experimental campaign for the production of η' mesons. One of the main goals was to measure the dynamics of η' → ηπ0π0 with high precision. An overview of the physics cases, the experimental setup and the results are given.