Observation of B⁰s - B⁻⁰s oscillations using partially reconstructed hadronic Bs decays

Abstract

This thesis describes the contribution of partially reconstructed hadronic decays in the world's first observation of B⁰s - B⁻⁰s oscillations. The analysis is a core member of a suite of closely related studies whose combined time-dependent measurement of the B⁰s - B⁻⁰s oscillation frequency Am, is of historic significance. Using a data sample of 1 fb-1 of pp collisions at V = 1.96 TeV collected with the CDF-II detector at the Fermilab Tevatron, we find signals of 3150 partially reconstructed hadronic B, decays from the combined decay channels ... These events are analyzed in parallel with 2000 fully reconstructed ... decays. The treatment of the data is developed in stages of progressive complexity, using high-statistics samples of hadronic Bo and B+ decays to study the attributes of partially reconstructed events. The analysis characterizes the data in mass and proper decay time, noting the potential of the partially reconstructed decays for precise measurement of B branching fractions and lifetimes, but consistently focusing on the effectiveness of the model for the oscillation measurement. We efficiently incorporate the measured quantities of each decay into a maximum likelihood fitting framework, from which we extract amplitude scans and a direct measurement of the oscillation frequency. The features of the amplitude scans are consistent with expected behavior, supporting the correctness of the calibrations for proper time uncertainty and flavor tagging dilution. The likelihood allows for the smooth combination of this analysis with results from other data samples, including 3500 fully reconstructed hadronic B, events and 61 500 partially reconstructed semileptonic B, events. The individual analyses show compelling evidence for B⁰s - B⁻⁰s oscillations, and the combination yields a clear signal. The probability that random fluctuations could produce a comparable signature is 8 x 10-8, which exceeds the 5 standard deviations threshold of significance for observation.

(cont.) The discovery threshold would not be achieved without inclusion of the partially reconstructed hadronic decays. We measure .... consistent with the Standard Model expectation.