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IAXO (International Axion Observatory)

The nature of dark matter is a driving question of 21st century physics. Dark matter has been inferred by its gravitational pull, which influences how the universe “clumps up” to form the large- scale structures that we observe. However, the properties of dark matter are inconsistent with any form of matter ever studied here on Earth, and because it does not absorb or reflect light, dark matter cannot be observed directly by standard astronomical techniques. Hence the hunt is on for a new fundamental particle form of matter.

Axions are among the best motivated candidates for dark matter. Specifically, axions are motivated by the Peccei-Quinn mechanism, arguably the only viable solution to the “strong CP” problem, or why the strong force seems not to violate charge-parity symmetry. Axion-like particles (ALPs) are a generic prediction of many Beyond the Standard Model physics scenarios, in particular string theory.

The International Axion Observatory (IAXO) is a next-generation axion helioscope, designed to search for axions from the Sun that are reconverted into X-ray photons via a strong laboratory magnetic field. IAXO will deliver a factor of 20 improvement in sensitivity over the current leading helioscope, the CERN Axion Solar Telescope (CAST), across a wide mass range extending up to 0.25 eV.

BabyIAXO, a preliminary experiment scheduled for 2026, will validate all key technologies at scale and deliver a factor of 5 improvement in sensitivity, already opening novel discovery space for axions and ALPs. In particular, IAXO and BabyIAXO are the only validated experimental designs capable of detecting QCD axions with masses > 10^3 eV, which are motivated by a variety of dark matter scenarios. Improving on the successful designof CAST, BabyIAXO will consist of a superconducting magnet with two bores, each instrumented with X-ray optics that focus the reconverted photons onto ultra-low background detectors.

At Nevis, we are constructing the inner core X-ray optic for BabyIAXO. This work will leverage the expertise and facilities from construction of the NuSTAR X-ray Observatory optics, on which the BabyIAXO and IAXO optics, as well as the prototype optic installed in CAST, are based.