Near-Quantum-Noise Axion Dark Matter Search at CAPP around 9.5  μeV.

Area of Science:

• * Particle Physics
• * Astrophysics
• * Cosmology

Background:

• * Axion dark matter is a leading candidate for non-baryonic dark matter.
• * Cavity experiments are a primary method for detecting axions.
• * Previous experiments were limited by receiver noise and scan speed.

Purpose of the Study:

• * To search for axion dark matter in the 9.39-9.51 μeV mass range.
• * To improve the sensitivity of axion detection experiments.
• * To exclude a range of two-photon coupling for the QCD axion.

Main Methods:

• * Implemented a flux-driven Josephson parametric amplifier (JPA) in a cryogenic receiver.
• * Achieved a system noise temperature of 200 mK, the lowest recorded for phase-insensitive JPA operation in axion cavity experiments.
• * Developed and utilized a two-stage scanning method to increase scan speed by 26%.

Main Results:

• * Achieved the lowest system noise temperature (200 mK) in published axion cavity experiments with phase-insensitive JPA operation.
• * Increased experimental scan speed by 26% using a novel two-stage scanning method.
• * Excluded a range of two-photon coupling for the QCD axion with an order of magnitude improvement in sensitivity.

Conclusions:

• * The enhanced receiver sensitivity and scanning speed significantly improve the prospects for axion dark matter detection.
• * This work sets new limits on the QCD axion parameter space.
• * The developed techniques pave the way for future, more sensitive axion searches.