From Bottom to Top: Identification to Precision Measurement of 3rd Generation Quarks with the ATLAS Detector

[摘要] The 3rd-generation quarks, bottom (b) and top (t), are recent additions to the Standard Model of particle physics, and precise characterization of their properties have important implications to searching for new physics phenomena. This thesis presents two analyses which use 4.6 fb−1 of pp collision data at √s = 7 TeV collected by the ATLAS detector at the Large Hadron Collider (LHC) to measure their properties. The first is an analysis which measures our ability to identify jets originating from b quarks with machine-learning algorithms applied to simulated and real data, so the result in simulation can be corrected to match that in data. This measurement has implications for our ability to identify processes with b quarks in their final state; t quarks decay to a b quark and a weak vector boson W more than 99% of the time. The second analysis presented measures properties of the t → Wb decay channel associated with phenomena not predicted by the Standard Model, through a set of effective couplings which preserve Lorentz covariance. The kinematic information of the final-state particles is used to construct an event-specific coordinate system, and probability density is estimated as a function of solid angle in these coordinates. A parameterization of the effective couplings is extracted via a novel unfolding method, finding their values consistent with the Standard Model expectation, contributing the first measurement of the correlation between the parameters, and improving on previous limits.

[发布机构] the University of Pittsburgh