- Salemi, Chiara P;
- Foster, Joshua W;
- Ouellet, Jonathan L;
- Gavin, Andrew;
- Pappas, Kaliroë MW;
- Cheng, Sabrina;
- Richardson, Kate A;
- Henning, Reyco;
- Kahn, Yonatan;
- Nguyen, Rachel;
- Rodd, Nicholas L;
- Safdi, Benjamin R;
- Winslow, Lindley
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.