Publication Date

2012-05-03

Availability

Open access

Embargo Period

2012-05-03

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Physics (Arts and Sciences)

Date of Defense

2012-04-19

First Committee Member

Massimiliano Galeazzi

Second Committee Member

Joshua Gundersen

Third Committee Member

Thomas Curtright

Fourth Committee Member

Tarek Saab

Abstract

With their existence first proposed in 1930, neutrinos have subsequently proven themselves as experts at avoiding detection. Until early this century, it was not even known if neutrinos were massive particles. With the results of neutrino oscillation experiments such as Super-Kamiokande and SNO, we now know that neutrinos have a non-zero mass. However, these experiments are only sensitive to the difference of the square of neutrino mass eigenstates and do not provide sufficient information to resolve the neutrino mass hierarchy. Several complimentary methods are being explored to obtain an absolute mass scale, but the most promising model-independent approach is high precision spectroscopy of the 𝛽-spectrum endpoint (Q-value). In general, all energy from the decay is detected except for that of the neutrino, which results in a correction near the endpoint of the spectrum that is related to the neutrino rest mass. To detect this difference requires excellent energy resolution. This may be obtained by utilizing a scalable approach consisting of microcalorimeter arrays with the 𝛽-decay source embedded in the absorber. Two such experiments, Troitsk and Mainz have been able to set an upper limit of 2.3 eV on the neutrino mass, but higher precision is needed. MARE (Microcalorimeter Arrays for a Rhenium Experiment) is the successor to these experiments and plans to obtain resolution in the sub-eV range. Using an analysis program developed at the University of Miami, we have been able to verify the creation of holmium-163 which has a higher activity than rehenium-187. A landmark in the MARE project, this higher activity can provide better statistics and reduces the live time and array size requirements for a given sensitivity. One of the primary limits on the sensitivity of the MARE project, related to the source activity, is the pile-up spectrum, which is the result of unresolved double pulses. We have developed a platform to explore the efficiency of different algorithms at detecting these difficult to resolve double pulses. Using this platform, we characterize the efficiency of two different algorithms (one of which we developed for this exact purpose). The resulting analysis demonstrates that it is possible to remove a significant fraction of these events with minimal false positives. By utilizing these algorithms, MARE will be able to achieve improved sensitivity yielding a higher precision neutrino mass value.

Keywords

Physics; Neutrino; MARE; Microcalorimeter; Astrophysics

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