First $��K$ atom lifetime and $��K$ scattering length measurements

The results of a search for hydrogen-like atoms consisting of $��^{\mp}K^{\pm}$ 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 ($178 \pm 49$) and from Coulomb final state interaction ($653 \pm 42$). Using these results the analysis yields a first value for the $��K$ atom lifetime of $��=(2.5_{-1.8}^{+3.0})$ fs and a first model-independent measurement of the S-wave isospin-odd $��K$ scattering length $\left|a_0^-\right|=\frac{1}{3}\left|a_{1/2}-a_{3/2}\right|= \left(0.11_{-0.04}^{+0.09} \right)M_��^{-1}$ ($a_I$ for isospin $I$).
14 pages, 8 figures