Measurement of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi><mml:mi>K</mml:mi></mml:math> atom lifetime and the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>π</mml:mi><mml:mi>K</mml:mi></mml:math> scattering length

After having announced the statistically significant observation ($5.6\ensuremath{\sigma}$) of the new exotic $\ensuremath{\pi}K$ atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding atom lifetime, based on the full $\ensuremath{\pi}K$ data sample: $\ensuremath{\tau}=(5.{5}_{\ensuremath{-}2.8}^{+5.0})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}\text{ }\text{ }\mathrm{s}$. By means of a precise relation ($\ensuremath{\approx}1%$) between atom lifetime and scattering length, the following value for the $S$-wave isospin-odd $\ensuremath{\pi}K$ scattering length ${a}_{0}^{\ensuremath{-}}=\frac{1}{3}({a}_{1/2}\ensuremath{-}{a}_{3/2})$ has been derived: $|{a}_{0}^{\ensuremath{-}}|=(0.07{2}_{\ensuremath{-}0.020}^{+0.031}){M}_{\ensuremath{\pi}}^{\ensuremath{-}1}$.