A study of the decay width difference in the B-s(0)-(B)over-bar(s)(0) system using phi phi correlations

Abstract In a data sample of about four million hadronic Z decays recorded with the ALEPH detector from 1991 to 1995, the B 0 s →D (∗)+ s D (∗)− s decay is observed, based on tagging the final state with two φ mesons in the same hemisphere. The D s (∗)+ D s (∗)− final state is mostly CP even and corresponds to the short-lived B 0 s mass eigenstate. The branching ratio of this decay is measured to be BR (B 0 s ( short ) →D (∗)+ s D (∗)− s ) =(23±10 −9 +19 )% . A measurement of the lifetime of the B 0 s (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 ΔΓ / Γ in the B 0 s – B 0 s system, corresponding to an average value ΔΓ / Γ =(25 +21 −14 )%.