Date of Degree
PhD (Doctor of Philosophy)
According to the Standard Model of particle physics, elementary particles interact via the exchange of mediator particles. The specific mediator particle depends on the force: gluons for the strong nuclear force, photons for the electromagnetic force, and W and Z bosons for the weak nuclear force. No quantum theory of gravity has been deemed adequate by the community at this time, and no gravity-mediating particle (graviton is the proposed name for such a particle) is included in the Standard Model. As gravity is much weaker than the other fundamental forces at the particle level, this does not currently pose practical difficulties for elementary particle physics.
In order to specifically study W and Z bosons, it is necessary to generate high-energy beams of particles, which are collided, and whose collisions (hopefully) produce the 90 GeV required for Z boson production. Typically, electrons and protons are the particle of choice for these beams. In order to obtain the necessary energies, circular collider facilities have been the highest energy sites for years. As electrons radiate energy when in circular orbits, by the late 1980's proton colliders have been the primary choice for high-energy physics. One such collider, built at Fermilab National Accelerator Laboratory in Batavia, Illinois, was the Tevatron, which started operations in 1984 and finally shut down in 2011.
The Tevatron collided protons with anti-protons with a center of mass energy of 1.96 TeV for ten years (2001-2011) after a series of upgrades known collectively as Run II. Of the two detectors at the Tevatron, this analysis considers events observed at the Collider Detector at Fermilab (CDF) during Run II. Results can be usefully cross-checked by the other detector, D0. This thesis includes a technical description of the silicon tracking system at the CDF detector, including an account of challenges encountered during its operation and some of the personal work done to assist in its continuing operation.
This analysis measures the frequency at which two bosons are created (specifically, a photon and a Z boson) in a particular decay channel (namely, the Z decays into two b quarks). This diboson production is frequently measured, but typically only in leptonic decays at hadron colliders, as there is less background in these channels. This analysis attempts to provide a useful confirmation on these experiments by analyzing the diboson production in an independent decay channel.
As the event signature is also produced by strong force interactions, this electroweak signal composes a relatively small fraction of the events observed at CDF. In order to distinguish between the two, an artificial neural network was trained to separate the signal events from the primary background. While the result was measured to be consistent with the Standard Model prediction, large statistical and significant systematic errors limit the utility of this measurement.
CDF, Diboson production
Copyright 2013 Timothy M. Harrington-Taber