Measurement of the $\ddot{I}€K$ atom lifetime and the $\ddot{I}€K$ scattering length

Abstract

After having announced the statistically significant observation (5.6~$\ddot{I}ƒ$) of the new exotic $\ddot{I}€K$ atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding atom lifetime, based on the full $\ddot{I}€K$ data sample: $\ddot{I}„=(5.5_{-2.8}^{+5.0})\cdot 10^{-15}s$. By means of a precise relation ($<1\%$) between atom lifetime and scattering length, the following value for the S-wave isospin-odd $\ddot{I}€K$ scattering length $a_0^{-}=\frac{1}{3}(a_{1/2}-a_{3/2})$ has been derived: $\left|a_0^{-}\right|=(0.072_{-0.020}^{+0.031})M_{\ddot{I}}{€}^{-1}$.

18 pages, 17 figures