Study of B_s~0-(B_s~0)-bar oscillations and B_s~0 lifetimes using hadronic decays of B_s~0 mesons

摘要

Oscillations of B_s~0 mesons have been studied in samples selected from about 3.5 million hadronic Z decays detected by DELPHI between 1992 and 1995. One analysis uses events in the exclusive decay channels: B_s~0 → D_s~- π~+ or D_s~- a_1~+ and B_s~0 → (D-bar)~0 K~- π~+ or (D-bar)~0 K~- a_1~+, where the D decays are completely reconstructed. In addition, B_s~0 - (B_s~0)-bar oscillations have been studied in events with an exclusively reconstructed D_s accompanied in the same hemisphere by a high momentum hadron of opposite charge. Combining the two analyses, a limit on the mass difference between the physical B_s~0 states has been obtained: Δm_(B_s~0) > 4.0 ps~(-1) at the 95% C.L. with a sensitivity of Δm_(B_s~0) = 3.2 ps~(-1). Using the latter sample of events, the B_s~0 lifetime has been measured and an upper limit on the decay width difference between the two physical B_s~0 states has been obtained: τ_(B_s~0) = 1.53_(-0.15)~(+0.16)(stat.) ± 0.07(syst.) ps ΔΓ_(B_s~0)/Γ_(B_s~0) < 0.69 at the 95% C.L. The combination of these results with those obtained using D_s~±l~(-+) sample gives: Δm_(B_s~0) > 4.9 ps~(-1) at the 95% C.L. with a sensitivity of Δm_(B_s~0) = 8.7 ps~(-1). τ_(B_s~0) = 1.46 ± 0.11 ps and ΔΓ_(B_s~0)/Γ_(B_s~0) < 0.45 at the 95% C.L.