Flavour oscillations and CP asymmetry in semileptonic B_s⁰ decays

Abstract

The B 0 s meson spontaneously transforms into its antiparticle (B 0 s). These 'flavour oscillations' occur periodically with a frequency that may be measured. The oscillation frequency is related to the fundamental parameters of the electroweak interaction. Measuring the frequency provides a constraint on the electroweak quark coupling parameter V ts and improves the constraint on V td. Furthermore, the amplitude of the oscillation process may be slightly different in B 0 s and B 0 s mesons due to CP violating nature of the weak interaction. This 'asymmetry' is expected to be small (a SM,s f s p2.06 0.57q 10 5), but may be enhanced (a s f s Op1%q) by new sources of CP violation. This thesis describes a search for B 0 s flavour oscillations and charge asymmetry in the B 0 s Ñ D s µ ν µ X (D s Ñ K 0 K) decay mode using 5.0 fb 1 of D0 data. A lower limit is placed on the oscillation frequency, ∆m s ¡ 9.9 ps 1 with an expected sensitivity to oscillations below 14.8 ps 1. The charge asymmetry is measured to be a s f s 0.018 0.025(stat) 0.002(syst). A combination of these measurements with other decay modes is also presented.