Measurement of the Oscillation Frequency of Bs Mesons in the Hadronic Decay Mode Bs → πDs(φπ)X with the D0 Detector at the Fermilab Tevatron Collider

The standard model (SM) of particle physics is a theory, describing three out of four fundamental forces. In this model the Cabibbo-Kobayashi-Maskawa (CKM) matrix describes the transformation between the mass and weak eigenstates of quarks. The matrix properties can be visualized as triangles in the complex plane. A precise measurement of all triangle parameters can be used to verify the validity of the SM. The least precisely measured parameter of the triangle is related to the CKM element |Vtd|, accessible through the mixing frequency (oscillation) of neutral B mesons, where mixing is the transition of a neutral meson into its anti-particle and vice versa. It is possible to calculate the CKM element |Vtd| and a related element |Vts| by measuring the mass differences Δmd (Δms) between neutral Bd and (bar B)d (Bs and (bar B)s) meson mass eigenstates. This measurement is accomplished by tagging the initial and final state of decaying B mesons and determining their lifetime. Currently the Fermilab Tevatron Collider (providing p(bar p) collisions at √s = 1.96 TeV) is the only place, where Bs oscillations can be studied. The first selection of the 'golden', fully hadronic decay mode Bs → πDs(φπ)X at D0 is presented in this thesis. All data, taken between April 2002 and August 2007 with the D0 detector, corresponding to an integrated luminosity of ∫ Ldt = 2.8 fb-1 is used. The oscillation frequency Δms and the ratio |Vtd|/|Vts| are determined as Δms = (16.6-0.4+0.5(stat)-0.3+0.4(sys)) ps-1, |Vtd|/|Vts| = 0.213-0.003+0.004(exp) ± 0.008(theor). These results are consistent with the standard model expectations and no evidence for new physics is observable.