Results from phase 1 of the HAYSTAC microwave cavity axion experiment

TL;DR

The HAYSTAC experiment conducted a microwave cavity search for axion dark matter in the 5.6-5.8 GHz range, setting new exclusion limits and demonstrating near-quantum-limited sensitivity with advanced amplification and cooling techniques.

Contribution

First phase results of HAYSTAC using a copper cavity and Josephson parametric amplifier, achieving unprecedented sensitivity and extending axion mass exclusion range.

Findings

Excluded axion-photon couplings above 2×10^{-14} GeV^{-1}

Achieved system noise temperature twice the Standard Quantum Limit

Extended axion mass exclusion range to 24.0 μeV

Abstract

We report on the results from a search for dark matter axions with the HAYSTAC experiment using a microwave cavity detector at frequencies between 5.6-5.8$\, \rm Ghz$. We exclude axion models with two photon coupling $g_{a\gamma\gamma}\,\gtrsim\,2\times10^{-14}\,\rm GeV^{-1}$, a factor of 2.7 above the benchmark KSVZ model over the mass range 23.15$\,<\,$$m_a \,$<$\,$24.0$\,\mu\rm eV$. This doubles the range reported in our previous paper. We achieve a near-quantum-limited sensitivity by operating at a temperature $T<h\nu/2k_B$ and incorporating a Josephson parametric amplifier (JPA), with improvements in the cooling of the cavity further reducing the experiment's system noise temperature to only twice the Standard Quantum Limit at its operational frequency, an order of magnitude better than any other dark matter microwave cavity experiment to date. This result concludes the first phase of the HAYSTAC program utilizing a conventional copper cavity and a single JPA.