QCD corrections to lifetime differences of B_s mesons

The calculation of QCD corrections to the width difference Delta Gamma in the B_s meson system is presented. The next-to-leading order corrections reduce the dependence on the renormalization scale significantly and allow for a meaningful use of hadronic matrix elements from lattice gauge theory. At present the uncertainty of the lattice calculations limits the prediction of Delta Gamma. The presented work has been performed in collaboration with Martin Beneke, Gerhard Buchalla, Christoph Greub and Alexander Lenz.