Conceptual Design of the International Axion Observatory (IAXO) (1401.3233v1)

Abstract: The International Axion Observatory (IAXO) will be a forth generation axion helioscope. As its primary physics goal, IAXO will look for axions or axion-like particles (ALPs) originating in the Sun via the Primakoff conversion of the solar plasma photons. In terms of signal-to-noise ratio, IAXO will be about 4-5 orders of magnitude more sensitive than CAST, currently the most powerful axion helioscope, reaching sensitivity to axion-photon couplings down to a few $\times 10^{-12}$ GeV$^{-1}$ and thus probing a large fraction of the currently unexplored axion and ALP parameter space. IAXO will also be sensitive to solar axions produced by mechanisms mediated by the axion-electron coupling $g_{ae}$ with sensitivity $-$for the first time$-$ to values of $g_{ae}$ not previously excluded by astrophysics. With several other possible physics cases, IAXO has the potential to serve as a multi-purpose facility for generic axion and ALP research in the next decade. In this paper we present the conceptual design of IAXO, which follows the layout of an enhanced axion helioscope, based on a purpose-built 20m-long 8-coils toroidal superconducting magnet. All the eight 60cm-diameter magnet bores are equipped with focusing x-ray optics, able to focus the signal photons into $\sim 0.2$ cm$^2$ spots that are imaged by ultra-low-background Micromegas x-ray detectors. The magnet is built into a structure with elevation and azimuth drives that will allow for solar tracking for $\sim$12 h each day.

• The paper presents IAXO as a fourth-generation axion helioscope that improves sensitivity by 4-5 orders of magnitude compared to CAST.
• It details a massive toroidal superconducting magnet with eight bores and focused x-ray optics that optimize axion–photon conversion.
• The design opens new experimental avenues by exploring unexplored axion parameter space and advancing dark matter research.

Conceptual Design of the International Axion Observatory (IAXO)

The International Axion Observatory (IAXO) represents a significant step forward in the search for axions and axion-like particles (ALPs), potentially solving key problems in particle physics such as the strong-CP problem and the dark matter enigma. The observatory is designed as a fourth-generation axion helioscope, a sophisticated instrument aimed at detecting these elusive particles that are hypothesized to originate from our Sun.

Design and Features of the IAXO

IAXO's conceptual design builds upon lessons learned from its predecessor, the CERN Axion Solar Telescope (CAST), but with enhanced capabilities. It employs a massive toroidal superconducting magnet with eight bores, each measuring 60 cm in diameter, and spanning 20 meters in length. This magnet configuration is integral to the experiment as it generates the strong magnetic fields necessary for axion-photon conversion, the mechanism that enables the detection of axions in the form of x-ray photons.

Equipped with state-of-the-art focusing x-ray optics, IAXO is designed to concentrate signal photons into precise spots of approximately 0.2 cm², subsequently imaged by ultra-low-background Micromegas x-ray detectors. This setup leverages the decade-long operational experience of the CAST experiment, while taking full advantage of cutting-edge advancements in detector sensitivity and resolution.

Sensitivity and Capabilities

One of the remarkable aspects of IAXO is its projected sensitivity, which is 4-5 orders of magnitude superior to that of CAST. This translates into an ability to explore axion-photon couplings down to a few $\times 10^{-12}$ GeV$^{-1}$. Such sensitivity is crucial for probing unexplored regions of the axion parameter space, particularly the mass range up to 0.25 eV, which includes theoretical regions predicted for the QCD axion.

Broad Implications and Future Directions

IAXO is designed not only to search for solar axions but also to investigate other potential axion production mechanisms, such as those mediated by axion-electron couplings. Its capabilities might also extend to the detection of axion-related phenomena entirely within laboratory settings, such as "light-shining-through-a-wall" experiments.

The implications of IAXO's research could be profound, potentially confirming the existence of axions and ALPs, which would necessitate a reevaluation of our understanding of particle physics and open new avenues in the search for dark matter. Moreover, its multi-bore, multi-detector setup allows for versatility in experimental design, enabling a broad spectrum of WISP searches.

Looking Ahead

While IAXO's conceptual design thoroughly capitalizes on existing technologies, further innovations in detector and magnet technologies could continue to enhance its performance. This includes the possible integration of alternative detection technologies such as TES or CCDs, and the exploration of additional physics cases like low-mass dark matter detection.

The successful realization of IAXO will establish it as a premier facility for axion and ALP research, potentially detecting or excluding axion models within the next decade and setting stringent constraints on ALP models. Such an achievement would significantly impact theoretical models and guide future experiments in particle physics and cosmology.