First Results from ABRACADABRA-10 cm: A Search for Sub-$μ$eV Axion Dark Matter (1810.12257v2)

Abstract: The axion is a promising dark matter candidate, which was originally proposed to solve the strong-CP problem in particle physics. To date, the available parameter space for axion and axion-like particle dark matter is relatively unexplored, particularly at masses $m_a\lesssim1\,\mu$eV. ABRACADABRA is a new experimental program to search for axion dark matter over a broad range of masses, $10^{-12}\lesssim m_a\lesssim10^{-6}$ eV. ABRACADABRA-10 cm is a small-scale prototype for a future detector that could be sensitive to the QCD axion. In this Letter, we present the first results from a 1 month search for axions with ABRACADABRA-10 cm. We find no evidence for axion-like cosmic dark matter and set 95% C.L. upper limits on the axion-photon coupling between $g_{a\gamma\gamma}<1.4\times10^{-10}$ GeV$^{-1}$ and $g_{a\gamma\gamma}<3.3\times10^{-9}$ GeV$^{-1}$ over the mass range $3.1\times10^{-10}$ eV - $8.3\times10^{-9}$ eV. These results are competitive with the most stringent astrophysical constraints in this mass range.

Insights from ABRACADABRA-10 cm: A Forefront in Axion Dark Matter Search

The search for dark matter (DM) remains at the forefront of contemporary physics, and axions are promising candidates that provide solutions to both the dark matter problem and the strong-CP problem in quantum chromodynamics. The recent work detailing the outcomes from the experimental efforts of ABRACADABRA-10 cm offers an in-depth exploration of sub-$\mu$eV axion dark matter, a mass range that remains inadequately explored by previous endeavors.

Experimental Novelty and Setup

The ABRACADABRA (A Broadband/Resonant Approach to Cosmic Axion Detection with an Amplifying B-field Ring Apparatus) project operates on an experimental blueprint to explore axion masses ranging from $10^{-12}$ eV to $10^{-6}$ eV. The ABRACADABRA-10 cm is a prototype which, despite its relatively modest dimensions compared to future projections, embodies the sophistication required to probe axion-photon couplings over a wide mass range. The apparatus features a superconducting toroidal magnet capable of generating a stable magnetic field; this field, in the presence of axion DM, is expected to induce an oscillating magnetic field detectable by superconducting quantum interference devices (SQUIDs).

The axion-induced magnetic field ($\mathbf{B}_a$) manifests as an oscillating signal, simplified in their expressions to a current density parallel to the static magnetic field, thus facilitating detection through a finely-tuned readout system designed to capture weak signals without excessive noise interference. The installation is shielded against external magnetic interference and thermalized to hinder vibrational disturbances, ensuring the integrity of the signal processing pathway from the axion-induced fields.

Results and Rigorous Analysis

Over a month of data collection, the experiment exhibited no definitive evidence for axion-like DM. Nonetheless, the ABRACADABRA-10 cm sets a competitive 95% confidence limit on the axion-photon coupling constant $g_{a\gamma\gamma}$, quantified between $1.4 \times 10^{-10}$ GeV$^{-1}$ and $3.3 \times 10^{-9}$ GeV$^{-1}$ across the explored mass spectrum ($3.1 \times 10^{-10}$ eV to $8.3 \times 10^{-9}$ eV). These constraints are notably competitive with, and in some sectors surpass, the constraints given by leading astrophysical observations like those from the CAST experiment.

A meticulous statistical framework underpinning this work involves analyzing the data through an elaborate profile likelihood approach to discern potential axion signals amid noise. The Erlang distribution serves as the backbone for modeling the background noise, aiding in establishing stringent upper limits on $\mathbf{B}_a$ and consequently $g_{a\gamma\gamma}$, thus minimizing the false-positive detections while maintaining sensitivity to actual signals.

Investigative Pathways and Broader Implications

The ABRACADABRA initiative creates an auspicious platform for subsequent advancements and scaling up endeavors. Resolving current parasitic impediments and enhancing the experimental layout with more refined quantum sensors could yield augmented sensitivity, potentially spanning broader frequency ranges or enforcing longer exposure periods. This prospect positions ABRACADABRA-10 cm not only as a prototype but as a methodical stepping stone into future large-scale detectors capable of probing the quintessential QCD axion parameter space.

The results from ABRACADABRA-10 cm contribute significantly to the axion search by territory previously less dominated by laboratory results, offering a tangible path forward in experimental dark matter searches. It sets the groundwork for experimental setups that could reveal phenomena intrinsic to axions, rendering detailed insights into the elusive nature of dark matter and fundamentally enhancing our understanding of particle physics.

In sum, the meticulous design, comprehensive analysis, and the intriguing preliminary results of the ABRACADABRA-10 cm manifest the efficacy of the adopted setup, undoubtedly promising further discoveries and developments in the field of axion dark matter research. As the venture scales, its complementarity to existing projects, such as those utilizing microwave cavity designs, promises a robust landscape for realizing significant advancements in both theoretical and experimental physics in the context of cosmic dark matter exploration.