# Search for axion dark matter using solid state nuclear magnetic resonance and superconducting magnetometers

• Starts: 12:00 pm on Wednesday, November 30, 2022
• Ends: 1:30 pm on Wednesday, November 30, 2022
One of the major unsolved questions of modern physics is the nature of dark matter, whose existence is inferred circumstantially 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 talk, we describe experiments which exploit the axion coupling to the nuclear electric dipole moment (nEDM). In the CASPEr-Electric experiment, the axion dark matter interacts with the nuclear spins of $^{207}$Pb and the effective electric field is provided by a ferroelectric crystal in which the $^{207}$Pb is embedded. CASPEr-Electric is a resonant search where axion dark matter would perturb the equilibrium magnetization of the $^{207}$Pb nuclear spin ensemble. The experiment is calibrated through pulsed nuclear magnetic resonance (NMR) experiments on the $^{207}$Pb 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 talk 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 19-20.5 and 21.5-22 neV (4.6 - 4.9 and 5.2 - 5.3 MHz). The upper bound on the nEDM coupling is $|g_d| < 4 \times 10^{-4} \, \text{GeV}^{-2}$ with 95 \% confidence.
Location:
SCI 352
Host
Speaker