The ORGAN Experiment: An axion haloscope above 15 GHz (1706.00209v2)

Abstract: We present first results and future plans for the Oscillating Resonant Group AxioN (ORGAN) experiment, a microwave cavity axion haloscope situated in Perth, Western Australia designed to probe for high mass axions motivated by several theoretical models. The first stage focuses around 26.6 GHz in order to directly test a claimed result, which suggests axions exist at the corresponding mass of $110~\mu$eV. Later stages will move to a wider scan range of 15-50 GHz ($60-210~\mu $eV). We present the results of the pathfinding run, which sets a limit on $g_{a\gamma\gamma}$ of $2.02\times 10^{-12} $eV$^{-1}$ at 26.531 GHz, or 110~$\mu$eV, in a span of 2.5 neV (shaped by the Lorentzian resonance) with $90 \%$ confidence. Furthermore, we outline the current design and future strategies to eventually attain the sensitivity to search for well known axion models over the wider mass range.

• The paper establishes constraints on the axion-photon coupling constant by limiting gₐγγ to 2.02×10⁻¹² eV⁻¹ at 26.531 GHz.
• It employs a static copper cavity and low-noise cryogenic HEMT amplifier to enhance the inverse Primakoff effect during its pathfinding run.
• The experiment paves the way for future scans and quantum-limited amplification advancements to further explore axion dark matter.

An Overview of the ORGAN Experiment: A High-Frequency Axion Haloscope

The quest to detect axions, a hypothesized component of dark matter, has led to an assortment of experimental approaches aimed at probing these elusive particles. The paper under discussion details the efforts and findings of the Oscillating Resonant Group AxioN (ORGAN) experiment, a high-frequency microwave cavity axion haloscope located in Perth, Western Australia.

The goal of the ORGAN experiment is to search for axions within the mass range of 60-210 μeV, corresponding to frequencies between 15-50 GHz. Notably, the first stage of the experiment is concentrated around 26.6 GHz to directly test a claimed anomaly—referred to as the Beck result—that suggests axions with a mass of approximately 110 μeV.

Results and Methodology

The ORGAN experiment has conducted a pathfinding run that establishes constraints on the axion-photon coupling constant, $g_{a\gamma\gamma}$, setting a limit of $2.02\times 10^{-12} \text{ eV}^{-1}$ at 26.531 GHz over a 2.5 neV bandwidth with 90% confidence. This stage utilized a static, non-frequency tunable copper cavity in conjunction with a low-noise HEMT amplifier chain operating at cryogenic temperatures. The signal extraction relies on the resonant enhancement of axion-induced photon conversion within the cavity mode when subjected to an external magnetic field.

Theoretical Implications

The theoretical framework underscores the complexity of detecting axions due to their unknown mass and weak coupling to photons. The experiment capitalizes on the inverse Primakoff effect, where axions convert into detectable photons within the presence of a magnetic field. This axion detection technique aligns with key theoretical models including the Peccei-Quinn framework and potential implications from the SMASH model which predicts high-mass axions.

Future Directions

The paper articulates a phased approach for the ORGAN experiment, projecting future scans from 15-50 GHz and developing quantum-limited amplification technologies. Stage II operations will span several years, progressively targeting higher frequencies. Besides enhancing the sensitivity through novel resonator designs and amplification techniques, collaborations focused on surpassing the quantum noise limit via quantum non-demolition measurements and squeezed states are instrumental in refining axion searches.

Conclusion and Speculation

Ultimately, the ORGAN experiment represents a seminal endeavor to rigorously test and potentially tighten the limits of axion-photon couplings in a previously unexplored high-mass regime. The implications extend towards dark matter particle searches, improving our understanding of WISPs and their role in cosmology. As experimental advances in axion detection mature, they promise to substantiate or refute prevailing hypotheses within the field, enriching the theoretical landscape with empirical evidence. The ORGAN experiment thus highlights a pivotal step forward in expanding the parameter space for axion searches, with its forthcoming stages poised to deliver further insights into this enigmatic dark matter candidate. The outcomes of this, and subsequent experiments, are likely to critically inform the broader scientific effort to demystify the nature of dark matter.