Date of this Version
We have performed the first direct measurement of the time-integrated flavor untagged charge asymmetry in semileptonic Bs0 decays ASLs,unit by comparing the decay rate of Bs0 →μ+Ds- νX, where Ds-→ φ π- and φ → K+K-, with the charge-conjugate B̅s0 decay rate. This sample was selected from 1.3 fb-1 of data collected by the D0 experiment in run II of the Fermilab Tevatron collider. We obtain ASLs,unit= [1.23 ± 0.97(stat) ± 0.17(syst)] x 10-2. Assuming that Δms/Γ̅s >> 1, this result can be translated into a measurement of the CP-violating phase in Bs0 mixing: ΔΓs/ Δmstanφs = [2.45 ± 1.93(stat) ± 0.35(syst)] x 10-2.