Search for Low-Mass Axion Dark Matter with ABRACADABRA-10 cm.

Two of the most pressing questions in physics are the microscopic nature of the dark matter that comprises 84% of the mass in the Universe and the absence of a neutron electric dipole moment. These questions would be resolved by the existence of a hypothetical particle known as the quantum chromodynamics (QCD) axion. In this work, we probe the hypothesis that axions constitute dark matter, using the ABRACADABRA-10 cm experiment in a broadband configuration, with world-leading sensitivity. We find no significant evidence for axions, and we present 95% upper limits on the axion-photon coupling down to the world-leading level g_{aγγ}<3.2×10^{-11} GeV^{-1}, representing one of the most sensitive searches for axions in the 0.41-8.27 neV mass range. Our work paves a direct path for future experiments capable of confirming or excluding the hypothesis that dark matter is a QCD axion in the mass range motivated by string theory and grand unified theories.

First Results from ABRACADABRA-10 cm: A Search for Sub-µeV Axion Dark Matter.

The axion is a promising dark matter candidate, which was originally proposed to solve the strong-CP problem in particle physics. To date, the available parameter space for axion and axionlike particle dark matter is relatively unexplored, particularly at masses m_{a}≲1 µeV. ABRACADABRA is a new experimental program to search for axion dark matter over a broad range of masses, 10^{-12}≲m_{a}≲10^{-6} eV. ABRACADABRA-10 cm is a small-scale prototype for a future detector that could be sensitive to the QCD axion. In this Letter, we present the first results from a 1 month search for axions with ABRACADABRA-10 cm. We find no evidence for axionlike cosmic dark matter and set 95% C.L. upper limits on the axion-photon coupling between g_{aγγ}<1.4×10^{-10} and g_{aγγ}<3.3×10^{-9} GeV^{-1} over the mass range 3.1×10^{-10}-8.3×10^{-9} eV. These results are competitive with the most stringent astrophysical constraints in this mass range.

Characterization of the Catania VIS for H2(+).

The Catania VIS 2.46 GHz source has been installed on a test stand at the Best Cyclotron Systems, in Vancouver, Canada, as part of the DAEδALUS and IsoDAR R&D program. Studies to date include optimization for H2 (+)/p ratio and emittance measurements. Inflection, capture, and acceleration tests will be conducted when a small test cyclotron is completed.