Polarized Ultracold Neutrons: their transport in diamond guides and potential to search for physics beyond the standard model
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Experiments with polarized â ultracold neutronsâ (UCN) offer a new way to measure the decay correlations of neutron beta decay; these correlations can be used to test the completeness of the Standard Model and predict physics beyond it. Ultracold neutrons are very low energy neutrons that can be trapped inside of material and magnetic bottles. The decay correlations in combination with the neutron and muon lifetimes experimentally find the first element (Vud) of the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. The CKM matrix is a unitary transform between the mass and weak eigenstates of the d, s and b quarks; if the matrix is not unitary this would imply that the Standard Model is not complete. Currently the first row of the CKM matrix is over 2 sigma from unitarity and Vud is the largest component of the row.
The UCNA experiment looks at the correlation between the polarization of the neutron and the momentum of the electron resulting from the beta decay of the neutron (the A-correlation). The keys to making a high precision measurement of A-correlation are a near 100% polarization of the neutrons that decay, lowâ backscatter electron detectors, and small, well characterized backgrounds. UCN can be 100% polarized by passing them through a seven Telsa magnetic field. The key to the UCNA experiment is keeping them polarized until they decay or are lost.
This dissertation covers the development of guides that are minimally depolarizing and efficient transporters of UCN and their use in the UCNA experiment. The entire guide development process is covered from conception to manufacturing and testing. This process includes development of a pulsed laser deposition, diamond-like carbon coating system and materials studies of the resulting coatings. After the initial studies of the guide coating, meterâ long sections of guide are tested with UCN to determine their depolarization and transport properties.
The guide technology developed in this dissertation has been used in the entire UCNA experiment. Also, this technology is currently the state of the art for polarized and non-polarized UCN guide systems and it is being implemented in several new UCN experiments.
- Doctoral Dissertations