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Dark Matter Axion Search with HAYSTAC Phase II

https://doi.org/10.1103/PhysRevLett.134.151006

Bai, Xiran; Jewell, M J; Echevers, J; van_Bibber, K; Droster, A; Esmat, Maryam H; Ghosh, Sumita; Graham, Eleanor; Jackson, H; Laffan, Claire; et al (April 2025, Physical Review Letters)

This Letter reports new results from the HAYSTAC experiment’s search for dark matter axions in our galactic halo. It represents the widest search to date that utilizes squeezing to realize subquantum limited noise. The new results cover

1.71 μ eV

of newly scanned parameter space in the mass ranges

17.28 - 18.44 μ eV

and

18.71 - 19.46 μ eV

. No statistically significant evidence of an axion signal was observed, excluding couplings

| g_{γ} | \geq 2.75 \times | g_{γ}^{KSVZ} |

and

| g_{γ} | \geq 2.96 \times | g_{γ}^{KSVZ} |

at the 90% confidence level over the respective region. By combining this data with previously published results using HAYSTAC’s squeezed state receiver, a total of

2.27 μ eV

of parameter space has now been scanned between

16.96 - 19.46 μ eV

μ eV

, excluding

| g_{γ} | \geq 2.86 \times | g_{γ}^{KSVZ} |

at the 90% confidence level. These results demonstrate the squeezed state receiver’s ability to probe axion models over a significant mass range while achieving a scan rate enhancement relative to a quantum-limited experiment. Published by the American Physical Society2025

Free, publicly-accessible full text available April 1, 2026

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