One of the major unsolved questions of modern physics is the nature of dark matter, whose existence is inferred from astronomical observations. There are numerous potential dark matter candidates: one strong contender is the axion. The axion was initially proposed to solve the strong CP problem of quantum chromodynamics but it was later realized that its properties make it simultaneously a good candidate for dark matter. Axions couple to the Standard Model in various ways. In this thesis, we describe experiments which exploit the axion coupling gd to the nuclear electric dipole moment (nEDM). In particular, in the presence of an external electric field, the axion perturbs the magnetization of an ensemble of nuclear spins due to this coupling.
In the CASPEr-Electric experiment, the axion dark matter interacts with the nuclear spins of 207Pb and the effective electric field is provided by a ferroelectric crystal in which the 207Pb is embedded. CASPEr-Electric is a resonant search where axion dark matter would perturb the equilibrium magnetization of the 207Pb nuclear spin ensemble. The experiment is calibrated through pulsed nuclear magnetic resonance (NMR) experiments on the 207Pb nuclei. The first generation of the experiment demonstrated the feasibility of this method and established limits on the nEDM coupling in the mass range of 162-166 neV (Compton frequency 39-40 MHz).
This thesis primarily focuses on the second generation of the CASPEr-Electric experiment, which probed axion dark matter at a lower frequency range of 4 - 5 MHz using superconducting quantum interference devices (SQUIDs). Our search established upper limits on the coupling for axion masses in the range 19.5-20.5 and 21.5-22 neV (4.6 - 5.0 and 5.2 - 5.3 MHz). The upper bound on the nEDM coupling is |gd| < 4 x 10-4, GeV-2 with 95 % confidence. / 2024-11-07T00:00:00Z
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/47476 |
| Date | 07 November 2023 |
| Creators | Adam, Janos |
| Contributors | Sushkov, Alexander |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial 4.0 International, http://creativecommons.org/licenses/by-nc/4.0/ |
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