Study of Bs Mixing at the D-Zero Detector at Fermilab Using the Semi-leptonic Decay Bs -> Ds mu nu X

Bs0 mixing studies provide a precision test of Charge-Parity violation in the Standard Model. A measurement of Δms constrains elements of the CKM quark rotation matrix [1], providing a probe of Standard Model Charge-Parity violation. This thesis describes a study of Bs0 mixing in the semileptonic decay Bs0 → Ds- μ+νX, where Ds- → φπ-, using data collected at the D-Zero detector at Fermi National Accelerator in Batavia, Illinois. Approximately 2.8 fb-1 of data collected between April 2002 and August 2007 was used, covering the entirety of the Tevatron's RunIIa (April 2002 to March 2006) and part of RunIIb (March 2006-August 2007). Taggers using both opposite-side and same-side information were used to obtain the flavor information of the Bs0 meson at production. The charge of the muon in the decay Bs0 → Ds-μ+νX was used to determine the flavor of the Bs0 at decay. The Bd0 mixing frequency, Δmd, was measured to verify the analysis procedure. A log-likelihood calculation was performed, and a measurement of Δms was obtained. The final result was Δms = 18.86 ± 0.80(stat.) ± 0.37(sys.) with a significance of 2.6σ