Periodic Reporting for period 2 - IAXOplus (Towards the detection of the axion with the International Axion Observatory)
Periodo di rendicontazione: 2020-04-01 al 2021-09-30
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. Dark Energy is an even more exotic ingredient, omnipresent in all points of the space-time, associated with the energy of the vacuum, and that drives the accelerated expansion of the Universe.
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 (SM) of particle physics, probably the most successful theory in the history of physics. A number of shortcomings of the theory and the fact that it does not account for the Dark Matter and Energy, prompt theorists to propose possible hypothetical extensions.
Some of these extensions predict the existence of axions (or other similar particle generically called axion-like particles or ALPs). Axions would be extremely light particles that interact very weakly 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 are predicted to be emitted by the core of the Sun. It is based on the use of 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 and ALP models.
The scope of the present project encompasses the realization of a first complete intermediate experimental stage, BabyIAXO, including prototypes of the IAXO magnet and detection systems. It will already provide relevant physics outcome in the time-frame of the current grant, 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.
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 (SM) of particle physics, probably the most successful theory in the history of physics. A number of shortcomings of the theory and the fact that it does not account for the Dark Matter and Energy, prompt theorists to propose possible hypothetical extensions.
Some of these extensions predict the existence of axions (or other similar particle generically called axion-like particles or ALPs). Axions would be extremely light particles that interact very weakly 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 are predicted to be emitted by the core of the Sun. It is based on the use of 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 and ALP models.
The scope of the present project encompasses the realization of a first complete intermediate experimental stage, BabyIAXO, including prototypes of the IAXO magnet and detection systems. It will already provide relevant physics outcome in the time-frame of the current grant, 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 the first half of the project, the work has focused on consolidating the international collaboration, advancing on the design of all parts of the BabyIAXO axion helioscope, to bring them to the point of start of construction, as well as preparing the management structure and the adequate host environment at DESY-Hamburg.
A letter of intent was submitted to DESY Physics Review Committee (PRC) on October 2018, followed by a full proposal in April 2019. An ad-hoc international panel exhaustively reviewed the proposal in a full-day session on 20 May 2019. As a result, DESY approved the project and preparatory actions at the host immediately started. This process culminated at the end of 2019, with the formal approval of a ~3 M€ investment to cover the expenses of hosting BabyIAXO at DESY.
In parallel, steady progress has been achieved with the design of all subsystems of BabyIAXO. A conceptual design was completed by the time of the DESY proposal on April 2019, and has been recently published. Already at this point, important improvements were introduced with respect to the preliminary design described at the grant’s proposal. More recently the tendering design of the BabyIAXO magnet was completed, and reviewed in detail in aspecial session of the DESY PRC in Novemeber 2020. Since then, quotations from companies to build parts of the magnet are being received.
The collaboration counts with the endorsement of the European Space Agency (ESA) to use one existing 70 cm x-ray optics (a spare optics made for the XMM x-ray astronomy mission) in one of the magnet bores. The collaboration plans to build a custom-made optic for the second bore. A first prototype of the low-background x-ray detector for BabyIAXO is already in operation at the host institution of the grant, the University of Zaragoza. A second prototype is under construction and will be tested underground at the Laboratorio Subterráneo de Canfranc (LSC). This action was reviewed and approved by the LSC scientifica committee end of 2020.
In addition, the physics case of the experiment is continuously being updated and extended. A comprehensive "physics potential" review of IAXO was published in 2019. Numerous studies (both from IAXO members and from colleagues in the community) have since then contributed to expand its physics impact. A particularly relevant case is the RADES concept, that studies the possibility of adding "haloscope-like" setups to the BabyIAXO magnet, to enjoy dark matter axion sensitivity, complementing the baseline program of the experiment.
In summary, the project has successfully advanced to the point that first steps of the construction phase are already taking place: e.g. preparation of the experiment’s drive mount and purchase of the superconducting cable for the magnet. So far, the milestones of the ERC grant for the period have been successfully accomplished. As anticipated in the proposal, the grant has had a catalyzing effect in attracting additional resources and cohering the efforts from different parts of the international collaboration. Moreover, the design of BabyIAXO has been improved and the project evolves to a fully-fledged axion helioscope experiment in itself (not just a prototyping stage of IAXO) with relevant physics potential.
A letter of intent was submitted to DESY Physics Review Committee (PRC) on October 2018, followed by a full proposal in April 2019. An ad-hoc international panel exhaustively reviewed the proposal in a full-day session on 20 May 2019. As a result, DESY approved the project and preparatory actions at the host immediately started. This process culminated at the end of 2019, with the formal approval of a ~3 M€ investment to cover the expenses of hosting BabyIAXO at DESY.
In parallel, steady progress has been achieved with the design of all subsystems of BabyIAXO. A conceptual design was completed by the time of the DESY proposal on April 2019, and has been recently published. Already at this point, important improvements were introduced with respect to the preliminary design described at the grant’s proposal. More recently the tendering design of the BabyIAXO magnet was completed, and reviewed in detail in aspecial session of the DESY PRC in Novemeber 2020. Since then, quotations from companies to build parts of the magnet are being received.
The collaboration counts with the endorsement of the European Space Agency (ESA) to use one existing 70 cm x-ray optics (a spare optics made for the XMM x-ray astronomy mission) in one of the magnet bores. The collaboration plans to build a custom-made optic for the second bore. A first prototype of the low-background x-ray detector for BabyIAXO is already in operation at the host institution of the grant, the University of Zaragoza. A second prototype is under construction and will be tested underground at the Laboratorio Subterráneo de Canfranc (LSC). This action was reviewed and approved by the LSC scientifica committee end of 2020.
In addition, the physics case of the experiment is continuously being updated and extended. A comprehensive "physics potential" review of IAXO was published in 2019. Numerous studies (both from IAXO members and from colleagues in the community) have since then contributed to expand its physics impact. A particularly relevant case is the RADES concept, that studies the possibility of adding "haloscope-like" setups to the BabyIAXO magnet, to enjoy dark matter axion sensitivity, complementing the baseline program of the experiment.
In summary, the project has successfully advanced to the point that first steps of the construction phase are already taking place: e.g. preparation of the experiment’s drive mount and purchase of the superconducting cable for the magnet. So far, the milestones of the ERC grant for the period have been successfully accomplished. As anticipated in the proposal, the grant has had a catalyzing effect in attracting additional resources and cohering the efforts from different parts of the international collaboration. Moreover, the design of BabyIAXO has been improved and the project 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, the first one of these likely within the grant period, i. e. in the next 3 to 4 years. 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.
This improvement should allow BabyIAXO to start exploring a region of axion and ALP models that is only reachable by this experimental technique. This region of models is of particular importance as it contains a fraction of the QCD axion models, that is, the original axion proposed to solve an important shortcoming of the Standard Model. These models are also motivated by some astrophysical observations and also by the possibility of being the Dark Matter component.
Finally, BabyIAXO will also fulfill its original goal of being a relevant technological demonstrator of the final IAXO. The BabyIAXO systems will have dimensions representative of the final infrastructure, and therefore they constitute risk-mitigating prototypes for IAXO. After its baseline physics program (beyond the current grant’s period) the BabyIAXO setup will remain available, in parallel to the construction of the full IAXO, to perform additional activities.
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.
This improvement should allow BabyIAXO to start exploring a region of axion and ALP models that is only reachable by this experimental technique. This region of models is of particular importance as it contains a fraction of the QCD axion models, that is, the original axion proposed to solve an important shortcoming of the Standard Model. These models are also motivated by some astrophysical observations and also by the possibility of being the Dark Matter component.
Finally, BabyIAXO will also fulfill its original goal of being a relevant technological demonstrator of the final IAXO. The BabyIAXO systems will have dimensions representative of the final infrastructure, and therefore they constitute risk-mitigating prototypes for IAXO. After its baseline physics program (beyond the current grant’s period) the BabyIAXO setup will remain available, in parallel to the construction of the full IAXO, to perform additional activities.
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.