A Search for Double Beta Decay in ⁷⁶Ge

Citation

Fisher, Peter Harrison (1988) A Search for Double Beta Decay in ⁷⁶Ge. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/fmvr-y629. https://resolver.caltech.edu/CaltechTHESIS:01222013-110618869

Abstract

This thesis describes a search for the double beta (ββ) decay of ⁷⁶Ge using an array of eight high purity, high resolution germanium detectors containing a total of 3.9 x 10²⁴ ⁷⁶Ge nuclei. There are three modes of ββ decay: neutrinoless (0ѵ)ββ decay, ββ decay with Majoron emission (x⁰ββ decay) and two neutrino (2ѵ)ββ decay. The first two modes violate lepton number conservation, while the third is allowed by the Standard Model. 0ѵββ decay may take place to the ground state of the daughter nucleus (0⁺ → 0⁺ transition) or to an excited state of the daughter nucleus (0⁺ → 2⁺ transition). The detector was operated for a total time of 2033 h (0.23 y) which translates to 1.30 kg-y. The background at the ββ decay transition energy was 0.53 counts keV⁻¹ y⁻¹ (10²³ ⁷⁶Ge nuclei)⁻¹. No evidence for double beta decay of any sort was found and the half life limits are T^0ѵ_½(0⁺ → 0⁺) > 1.2 x 10²³ y, T^0ѵ_½(0⁺ → 2⁺) > 2 x 10²² y, T^χo_½ > 8 x 10²⁰ y, and T^2ѵ_½ > 2 x 10²⁰ y, all at 90% c.l. The limit for the neutrinoless mode translates to an upper limit of between 16 and 1.6 eV on the Majorana mass of the neutrino, depending on the nuclear matrix element used.

Thesis Files