B-bar B mixing in SLD

The mixing of B0 and bar B0 is one of the most important topics in B physics because the mixing occurs through second order weak box diagrams involving t to d and t to s quark transitions. The mixing parameters are thus sensitive to the CKM matrix elements Vtd and Vts which are presently difficult to assess experimentally in other ways. Mixing in the B0d system has been observed in the ARGUS, CLEO and UA1 detectors. They measured the mixing integrated over time xd=mixed/(mixed + unmixed) = (1/2)x2d/(1+(xd)2), and obtained a value of xd ∼ 0.7 where xd is defined as Δ/Γ in the B0d system. Since Vts is expected to be larger than Vtd, the authors expect the mixing to be substantially larger in the B0s system. In this case, χs → 1/2 and a time integrated mixing measurement is not very sensitive to xs. It is thus imperative to measure the time dependence of B0s mixing which is proportional to cos(xst) and is thus sensitive to xs in the expected range of values. At this time there is a preliminary measurement from ALEPH of the time dependence of B0d mixing, but there are no measurements of the time dependence of B0s mixing. Such a measurement is one of the aims of an extended SLD program