Measurement of the decay $\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^0\ddot{I}{€}^0\hat{I}\cdot$ at MAMI

Abstract

An experimental study of the $\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^0\ddot{I}{€}^0\hat{I}\cdot \to 6{\hat{I}}^3$ decay has been conducted with the best up-to-date statistical accuracy, by measuring $\hat{I}{\cdot }^{\prime }$ mesons produced in the ${\hat{I}}^{3}p\to \hat{I}{\cdot }^{\prime }p$ reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the $\hat{I}{\cdot }^{\prime }\to \ddot{I}{€}^0\ddot{I}{€}^0\hat{I}\cdot$ matrix element are consistent with the most recent results for $\hat{I}{\cdot }^{\prime }\to \ddot{I}€\ddot{I}€\hat{I}\cdot$ decays, but have smaller uncertainties. The available statistics and experimental resolution allowed, for the first time, an observation of a structure below the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the $\ddot{I}€\ddot{I}€$ scattering length combination, $a_0-a_2$, extracted from $K\to 3\ddot{I}€$ decays.

15 pages, 8 figures, 2 tables, accepted for publication in Phys. Rev. D