First πK atom lifetime and πK scattering length measurements

The results of a search for hydrogen-like atoms consisting of K mesons are presented. Evidence for K atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic K pairs from their breakup in the same target (178 49) as well as in terms of produced K atoms (653 42). Using these results, the analysis yields a first value for the K atom lifetime of = (2.5 +3.0 -1.8 ) fs and a first measurement of the S-wave isospin-odd K scattering length |a - 0 | = 1 3 |a 1/2a 3/2 | = (0.11 +0.09 -0.04 )M -1 (a I for isospin I).