Search for the $\hat{I}\cdot$ mesic ${}^3$He in the $pd\to dp\ddot{I}{€}^0$ reaction with the WASA-at-COSY facility

Abstract

The excitation function for the $pd\to$ $dp\ddot{I}{€}^0$ reaction has been measured by WASA-at-COSY experiment with the aim of searching for $^{3}\hspace{-0.03cm}\mbox{He}$-$\hat{I}\cdot$ mesic nuclei. The measurement in the vicinity of $\hat{I}\cdot$ meson production was performed using a ramped proton beam. The data analysis and interpretation was carried out with the assumption that the $\hat{I}\cdot$-mesic Helium decays via the formation of an intermediate N${}^{\ast }$(1535) resonance. No direct signal of the $\hat{I}\cdot$-mesic nucleus is observed in the excitation function. We determine a new improved upper limit for the total cross section for the bound state production and decay in the $pd\to$ $(^{3}\hspace{-0.03cm}\mbox{He}$-$\hat{I}\cdot {)}_{bound}\to$ $dp\ddot{I}{€}^0$ process. It varies between 13 nb to 24 nb for the bound state with width in the range $\hat{I}“\in (5,50)$ MeV.