B0–B̄ 0 mixing and decay constants with the non-perturbatively improved action Original Research Article

Several quantities relevant to phenomenological studies of B0–B̄ 0 mixing are computed on the lattice. Our main results are fBdB̂Bd=206(28)(14)+31−00 MeV, ξ=fBsB̂Bs/fBdB̂Bd= 1.16(7). We also obtain the related quantities fBsB̂Bs=237(18)(10)+34−00 MeV, fBd= 174(22)+7+5+26−0−0−00 MeV, fBs=204(15)+7+4+31−0−0−00 MeV, fBs/fBd=1.17(4)+0−1, fBd/fDs=0.74(5). After combining our results with the experimental world average Δmd(exp.), we predict Δms=15.8(2.1)(3.3) ps−1. We have also computed the relevant parameters for D0–D̄ 0 mixing which may be useful in some extensions of the Standard Model. All the quantities were obtained from a quenched simulation with a non-perturbatively improved Clover action at β=6.2, corresponding to a lattice spacing a−1=2.7(1) GeV, on a sample of 200 gauge-field configurations. A discussion of the main systematic errors is also presented. The quenching errors are not included in the systematic error estimates.