First πK atom lifetime and πK scattering length measurements

Abstract The results of a search for hydrogen-like atoms consisting of π ∓ K ± mesons are presented. Evidence for πK atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic πK pairs from their breakup in the same target ( 178 ± 49 ) as well as in terms of produced πK atoms ( 653 ± 42 ). Using these results, the analysis yields a first value for the πK atom lifetime of τ = ( 2.5 − 1.8 + 3.0 ) fs and a first measurement of 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 ).