First πK atom lifetime measurement and recent results from the DIRAC experiment

We report evidence for πK atoms production, using 24 GeV/ c proton beam from CERN PS interacting with a thin Ni target. We have identified (178 ± 49) πK pairs, which were produced in a bound state — πK atom, which was subsequently broken-up (ionized) in the Ni target. Our analysis yields a first measurement of the πK 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 πK scattering length | a 0 − | = 1/3| a 1/2 − a 3/2 | = (0.11 −0.04 +0.09 ) M π −1 ( a I for isospin I ).