Measurements of semileptonic mixing asymmetries for B0 and Bs0 mesons

We present measurements of the semileptonic mixing asymmetries for B(s)0 mesons, asld(s), using a data sample corresponding to 10.4fb−1 of pp¯ collisions at s=1.96TeV collected with the D0 experiment at the Fermilab Tevatron collider. For the asld measurement, two independent decay channels are used: B0→μ+D−X, with D−→K+μ−μ−; and B0→μ+D⁎−X, with D⁎−→D¯0μ−, D¯0→K+π−. For the asls measurement, the channel Bs0→μ+Ds−X, with Ds−→ϕμ−, ϕ→K+K− is used. For each channel, we extract the raw charge asymmetries, correct for detector-related asymmetries using data-driven methods, and account for dilution from charge-symmetric processes using Monte Carlo simulation. The final asld measurement combines four visible proper decay length regions for each channel, yielding asld=[0.68±0.45(stat.)±0.14(syst.)]%. This is the single most precise measurement of this parameter, with uncertainties smaller than the current world average of B factory measurements. Using the Bs0 meson sample, we make a single time-integrated measurement, asls=[−1.12±0.74(stat.)±0.17(syst.)]%. Both measurements are in agreement with the standard model predictions.