Measurement of the $\pi K$ atom lifetime and the $\pi K$ scattering length

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