Periodic Reporting for period 4 - IAXOplus (Towards the detection of the axion with the International Axion Observatory)
Reporting period: 2023-04-01 to 2024-08-31
We know that the majority of the Universe’s contents are non-luminous and of a nature very different from conventional matter. Dark Matter is five times more abundant that conventional matter, and determines the dynamics and evolution of galaxies and of the Universe as a whole. The dilucidation of the nature of this Dark Universe is an outstanding question in modern science, and connects with our understanding of the reality at the most fundamental level.
Modern particle physics allows us to understand and describe the nature and dynamics of all known subatomic constituents of our reality, as observed in our laboratories and accelerators. This knowledge is embodied in the Standard Model of particle physics. A number of shortcomings of the theory and the fact that it does not account for the Dark Matter, prompt theorists to propose possible hypothetical extensions.
Some of these extensions predict the existence of axions, extremely light particles that interact very feebly with conventional particles. Dark Matter could be made of axions. In addition, some intriguing astrophysical observations might be interpreted as hints of their existence.
The International Axion Observatory IAXO is one of the most ambitious experiments to find the axion. Its baseline configuration relies on the axion helioscope concept, which aims at detecting the axions that would be emitted by the core of the Sun. It will use a large magnet to trigger the conversion of solar axions into photons. IAXO will go well beyond current experiments' sensitivity and will probe a large fraction of axion models.
The scope of the present project encompasses the realisation of a first complete intermediate experimental stage, BabyIAXO, including prototypes of the IAXO magnet and detection systems. BabyIAXO will already provide relevant physics outcome, while preparing the ground for, and extending the physics reach of, the full IAXO. In particular, BabyIAXO will already be able to test a number of axion and ALP models that are invoked by the aforementioned astrophysical hints and therefore at this stage there is potential for discovery.
Modern particle physics allows us to understand and describe the nature and dynamics of all known subatomic constituents of our reality, as observed in our laboratories and accelerators. This knowledge is embodied in the Standard Model of particle physics. A number of shortcomings of the theory and the fact that it does not account for the Dark Matter, prompt theorists to propose possible hypothetical extensions.
Some of these extensions predict the existence of axions, extremely light particles that interact very feebly with conventional particles. Dark Matter could be made of axions. In addition, some intriguing astrophysical observations might be interpreted as hints of their existence.
The International Axion Observatory IAXO is one of the most ambitious experiments to find the axion. Its baseline configuration relies on the axion helioscope concept, which aims at detecting the axions that would be emitted by the core of the Sun. It will use a large magnet to trigger the conversion of solar axions into photons. IAXO will go well beyond current experiments' sensitivity and will probe a large fraction of axion models.
The scope of the present project encompasses the realisation of a first complete intermediate experimental stage, BabyIAXO, including prototypes of the IAXO magnet and detection systems. BabyIAXO will already provide relevant physics outcome, while preparing the ground for, and extending the physics reach of, the full IAXO. In particular, BabyIAXO will already be able to test a number of axion and ALP models that are invoked by the aforementioned astrophysical hints and therefore at this stage there is potential for discovery.
During a first stage of the project, the work focused on consolidating the international collaboration, bringing the design of all parts of the BabyIAXO axion helioscope to the point of start of construction, as well as preparing the management structure and the adequate host environment at DESY-Hamburg. A first design of BabyIAXO was completed, enhancing its figure-of-merit according to the project’s goal, and showing the viability of its construction and operation as a fully-fledged axion helioscope with relevant physics case. After that, first construction actions have started, although with some delay with respect the original plan, especially regarding the large 10-m long superconducting magnet needed for the experiment. The latter is due primarily the difficulties to procure the special type of superconducting conductor needed for the magnet, not available in industry at the time. Only in a later stage of the project a realistic construction roadmap has been established, and a more detailed and improved design of the BabyIAXO magnet was successfully reviewed in 2024.
In other fronts, the project has satisfactorily achieved the required objectives. The collaboration has secured the endorsement of the European Space Agency (ESA) to use one existing 70 cm x-ray optics (XMM spare optics) in one of the magnet bores. An additional custom-made optic is being built within the IAXO collaboration for the second bore. Several prototypes of the low-background Micromegas x-ray detector for BabyIAXO have been built and tested as part of the project. One of them was commissioned underground at the Laboratorio Subterráneo de Canfranc (LSC), showing record background levels and reaching the BabyIAXO target. Another one, running above-ground at CAPA-Zaragoza, has defined the roadmap towards actively tagging cosmic-induced background events down to the required level. Yet another one (dubbed IAXO pathfinder), took axion-sensitive data in the CAST experiment at CERN, producing a new world-record upper limit to the axion-photon coupling in 2024. The project has also produced the needed software/analysis tooling needed for BabyIAXO (dubbed REST-for-Physics).
In addition, the physics case of the experiment has been substantially extended. A comprehensive "physics potential" review was published in 2019. Numerous studies have since then contributed to expand its physics impact. A particularly relevant case is the RADES concept, proposing "haloscope-like" setups to also search for dark matter axions with BabyIAXO. A conceptual study of a haloscope inside the BabyIAXO magnet was published in 2023. This initial side-topic of the project has grown in relevance to the point of constituting the seed of what later has become a successful ERC-SyG project (DarkQuantum) to start in 2024. This will boost and extend the physics reach of BabyIAXO and is considered a big success of the present project.
In summary, even if the BabyIAXO infrastructure is not yet completed, the project has successfully demonstrated its technical viability, has gathered the needed community momentum and support, and has placed the project well on-track under construction. As anticipated in the proposal, the grant has had a catalysing effect in attracting additional resources and cohering the efforts from the international collaboration. Most goals have been successfully accomplished, and BabyIAXO evolves to a fully-fledged axion helioscope experiment in itself (not just a prototyping stage of IAXO) with relevant physics potential.
In other fronts, the project has satisfactorily achieved the required objectives. The collaboration has secured the endorsement of the European Space Agency (ESA) to use one existing 70 cm x-ray optics (XMM spare optics) in one of the magnet bores. An additional custom-made optic is being built within the IAXO collaboration for the second bore. Several prototypes of the low-background Micromegas x-ray detector for BabyIAXO have been built and tested as part of the project. One of them was commissioned underground at the Laboratorio Subterráneo de Canfranc (LSC), showing record background levels and reaching the BabyIAXO target. Another one, running above-ground at CAPA-Zaragoza, has defined the roadmap towards actively tagging cosmic-induced background events down to the required level. Yet another one (dubbed IAXO pathfinder), took axion-sensitive data in the CAST experiment at CERN, producing a new world-record upper limit to the axion-photon coupling in 2024. The project has also produced the needed software/analysis tooling needed for BabyIAXO (dubbed REST-for-Physics).
In addition, the physics case of the experiment has been substantially extended. A comprehensive "physics potential" review was published in 2019. Numerous studies have since then contributed to expand its physics impact. A particularly relevant case is the RADES concept, proposing "haloscope-like" setups to also search for dark matter axions with BabyIAXO. A conceptual study of a haloscope inside the BabyIAXO magnet was published in 2023. This initial side-topic of the project has grown in relevance to the point of constituting the seed of what later has become a successful ERC-SyG project (DarkQuantum) to start in 2024. This will boost and extend the physics reach of BabyIAXO and is considered a big success of the present project.
In summary, even if the BabyIAXO infrastructure is not yet completed, the project has successfully demonstrated its technical viability, has gathered the needed community momentum and support, and has placed the project well on-track under construction. As anticipated in the proposal, the grant has had a catalysing effect in attracting additional resources and cohering the efforts from the international collaboration. Most goals have been successfully accomplished, and BabyIAXO evolves to a fully-fledged axion helioscope experiment in itself (not just a prototyping stage of IAXO) with relevant physics potential.
Thanks in good part to the ERC grant, BabyIAXO is now considered a full experimental stage that will deliver relevant physics outcome. Once completed, BabyIAXO will operate as a fully-fledged axion helioscope experiment in itself (not just a prototyping stage of IAXO) with relevant physics potential. BabyIAXO will surpass the sensitivity of the best current bounds on the axion-photon coupling from the CAST experiment, the previous best axion helioscope. In fact, latest estimates are that BabyIAXO will improve the signal-to-noise-ratio of CAST by about a factor 100. A small anticipation of these results was achieved during the project by running the "IAXO pathfinder" in the CAST experiment and getting a new best-bound for CAST, slightly improving the previous one. This improvement should allow BabyIAXO to start exploring a very motivated un-explored region of axion models. BabyIAXO will also fulfil its original goal of being a relevant technological demonstrator of the final IAXO. The BabyIAXO systems will constitute risk-mitigating prototypes for IAXO.
BabyIAXO will start an exciting and promising program of axion research that will prepare the ground for the full IAXO. This program has unique features among the wider axion experimental landscape, with very promising prospects, not excluding the possibility of a discovery. This discovery might already come at the BabyIAXO stage. The detection of the axion or other similar fundamental particle would be the first direct measurement of a particle clearly outside the Standard Model, shedding light on the theory beyond it. Potentially also solving the Dark Matter problem, it would constitute a Nobel-winnng discovery that would lead to a breakthrough in Particle Physics, Cosmology and Astrophysics.
BabyIAXO will start an exciting and promising program of axion research that will prepare the ground for the full IAXO. This program has unique features among the wider axion experimental landscape, with very promising prospects, not excluding the possibility of a discovery. This discovery might already come at the BabyIAXO stage. The detection of the axion or other similar fundamental particle would be the first direct measurement of a particle clearly outside the Standard Model, shedding light on the theory beyond it. Potentially also solving the Dark Matter problem, it would constitute a Nobel-winnng discovery that would lead to a breakthrough in Particle Physics, Cosmology and Astrophysics.