First $nK$ atom lifetime measurement and recent results from the DIRAC experiment

We report evidence for $\pi K$ atoms production, using 24 GeV/c proton beam from CERN PS interacting with a thin Ni target. We have identified $(178 \pm 49) \pi K$ pairs, which were produced in a bound state - $\pi K$ atom, which was subsequently broken-up (ionized) in the Ni target. Our analysis yields a first measurement of the $\pi K$ atom lifetime $(2.5_{-1.8}^{+3.0})$ fs [1]. This lifetime is connected in a model-independent way to the S-wave isospin-odd $\pi K$ scattering length $|a_0^-| = \frac{1}{3}|a_{1/2} - a_{3/2}| = (0.11_{-0.04}^{+0.09}) M_{\pi}^{-1}$ ($a_I$ for isospin $I$).