First $\ddot{I}€K$ atom lifetime and $\ddot{I}€K$ scattering length measurements

Abstract

The results of a search for hydrogen-like atoms consisting of $\ddot{I}{€}^{\mp }{K}^{\pm }$ mesons are presented. Evidence for $\ddot{I}€K$ atom production by 24 GeV/c protons from CERN PS interacting with a nickel target has been seen in terms of characteristic $\ddot{I}€K$ 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 $\ddot{I}€K$ atom lifetime of $\ddot{I}„=(2.5_{-1.8}^{+3.0})$ fs and a first model-independent measurement of the S-wave isospin-odd $\ddot{I}€K$ scattering length $\left|a_0^{-}\right|=\frac{1}{3}\left|a_{1/2}-a_{3/2}\right|=\left(0.11_{-0.04}^{+0.09}\right)M_{\ddot{I}}{€}^{-1}$ ($a_I$ for isospin $I$).

14 pages, 8 figures