Barate, R (reprint author), CNRS, IN2P3, Phys Particules Lab, LAPP, F-74019 Annecy Le Vieux, France.
In a data sample of about four million hadronic Z decays recorded with the ALEPH detector from 1991 to 1995. the B-s(0) --> (Ds(*)+Ds()*()-) decay is observed, based on tagging the final state with two phi mesons in the same hemisphere. The D-s((*)+) D-s((*)-) final state is mostly CP even and corresponds to the short-lived B-s(0) mass eigenstate. The branching ratio of this decay is measured to be BR(B-s(0)(short) --> D-s((*)+) D-s((*)-)) = (23 +/- 10(-9)(+19))%. A measurement of the lifetime of the B-s(0)(short) gives 1.27 +/- 0.33 +/- 0.08 ps. The lifetime and branching ratio measurements provide two essentially independent methods of estimating the relative decay width difference Delta Gamma/Gamma in the B-s(0)-(B) over bar(s)(0) system, corresponding to an average value Delta Gamma/Gamma = (25+/-(21)(14))%. (C) 2000 Elsevier Science B.V. All rights reserved.