Searching for axionlike dark matter using nuclear magnetic resonance and precision magnetometry
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Astrophysical observations indicate the existence of dark matter through its gravitational interaction, but since its other interactions remain undetected, its particle nature is still unknown. There are several dark matter candidates, one being a hypothetical particle called axion that can have three types of non-gravitational couplings: electromagnetic, electric dipole moment (EDM), and gradient. This dissertation presents experimental approaches and axionlike dark matter search results from two table-top experiments: Cosmic Axion Spin Precession Experiment (CASPEr-electric) sensitive to EDM and gradient couplings, and Search for Halo Axions with Ferromagnetic Toroids (SHAFT) sensitive to electromagnetic coupling. CASPEr-electric is a resonant search for axionlike dark matter through the induced nuclear spin precession. The experimental approach is measuring nuclear magnetic resonance (NMR) of the heavy atom in a ferroelectric crystal. Experimental setup is characterized using pulsed NMR calibration measurements. Recorded search data that is sensitive to axionlike dark matter is analyzed by optimal filtering and then setting a detection threshold based on the histogram of power spectral density modeled as a Gaussian distribution. The candidates above the threshold are all rejected through statistical fluctuations and scan/re-scan measurements. CASPEr-electric places the upper bounds on the EDM and gradient couplings of axionlike dark matter in the Compton frequency range from 39.1 MHz to 40.2 MHz. SHAFT is a broadband search for axionlike dark matter through the induced oscillatory magnetic field. The resultant magnetic flux is measured with a precision magnetometer called superconducting quantum interference device (SQUID), coupled to a coil placed on the inner surface of a ferromagnetic toroid. After analyzing the search data, all candidates are rejected and SHAFT places a limit on electromagnetic coupling of axionlike dark matter between 3 kHz and 3 MHz Compton frequencies. Finally, coupling limits placed by CASPEr-electric and SHAFT are evaluated in the wider parameter space, and possible future directions that both experiments could take to improve their sensitivities to axionlike dark matter are discussed.