Axions and relatives across different mass scales

Project Information

AxScale

Grant agreement ID: 802836

DOI

10.3030/802836

Project closed

EC signature date 24 August 2018

Start date 1 November 2018

End date 31 October 2025

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 134 375,00

EU contribution

€ 1 134 375,00

Coordinated by

MAX-PLANCK-GESELLSCHAFT ZUR FORDERUNG DER WISSENSCHAFTEN EV
Germany

Periodic Reporting for period 5 - AxScale (Axions and relatives across different mass scales)

Reporting period: 2024-05-01 to 2025-10-31

Summary of the context and overall objectives of the project

The majority of the Universe’s constituents are non-luminous, or “dark”, and in fact behaving very differently from the matter that we see in our every-day's lives. One of these constituents is the “Dark Matter”: It is around five times more abundant than the every-day matter that surrounds us: Dark Matter determines the dynamics of galaxies like our own, as well as its evolution: Without the gravitational pull of Dark Matter, the Universe as we know it would not exist. The quest to understand the nature of Dark Matter belongs to a set of unsolved problems in fundamental physics, often referred to as `physics beyond the Standard Model’. In may be that such `physics beyond the Standard Model’ may be found only at the highest energies, and thus is accessible only at high-energy colliders. The AxScale project aimed at testing a different, intriguing possibility: “What if new physics is instead light-weight, but extremely weakly coupled?”
Using two complementary experimental lever-arms, the AxScale project pursued the answer to this question. The prime example of a well-motivated, weakly interacting particle of comparably low mass is the axion. It could make up all the Dark Matter but is also connected to another fundamental mystery in particle physics.
In AxScale the scope of the project was to search in a comprehensive way for axions and related new physics particles at two complementary experiments: At the NA62 experiment at CERN, weakly coupled new physics such as axions, were searched in data taken in beam-dump mode and in data from ultra-rare decays of a Kaon. If the axion were to be very light-weight and make up the Dark Matter, its mass could be determined through a dedicated experiment, called RADES. The AxScale project thus stood out by the fact that it could test new physics in two vastly differing and independent experiments and thereby partially cross-check its own findings.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

For the NA62 experiment at CERN, the performed work and the achievements can be grouped in three parts (albeit the division being fluid in parts): phenomenology, data-taking and analysis. Before doing any new physics experiment, we scrutinized past work in order to assess our best course of action: “Are we sure that what we do hasn’t been done before and not interpreted in modern theoretical terms?“ In the phenomenological publications of AxScale we studied theoretically the impact of certain measurements with a given statistics and compared it to modern theoretical interpretations of previous literature. We also made the tools to enable these estimates publicly available so that they can be extended and improved by anyone who would like to contribute to the field. We moved on to data-taking, which involved an iterative approach to find the ideal conditions. Finally, we conducted and published several data analyses. Albeit no new particle was found, thanks to AxScale, NA62 became one of the leading players in the search for weakly interacting particles at the MeV-GeV scale but also to sub-eV axion searches with accelerators.

For RADES, the project can be grouped in two periods: In the first period, at CERN, we made parasitic use of available infrastructure needed in axion Dark Matter search experiments: Cryogenics and strong-field magnets. We developed a number of innovative new cavity geometries, and among other results, published results of the first axion Dark Matter search employing high-temperature superconducting tapes on the cavity surfaces. In the second period, at the Max Planck Institute for Physics (MPP) in Garching, two dedicated labs were equipped and set-up with a dilution fridge and a 12T magnet. This enabled the research team to expand their R&D and work towards connecting axion dark matter searches with novel quantum technologies. During the time at MPP, the RADES experiment evolved into a fully-fledged collaboration, counting on international, interdisciplinary expertise to scale the experiment to its sensitivity beyond the state-of-the art.

In both AxScale sub-projects, results were disseminated widely through articles in popular science magazines (such as “Spectrum der Wissenschaft”), interactive set-ups at “open day events” and events targeted at girl’s in STEM.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

In the phenomenological context of the research in NA62, several achievements have been made that go beyond the state-of the art: For many years, phenomenological estimates for the new physics reach of experiments of this kind have been published purely solely with the obtained final sensitivity results, without any way of rasily reproducing these results. Within AxScale, the public software tool ALPINIST was developed. This software tool not only made all calculations and assumptions behind estimates public and transparent, but established a tool to put future estimates on the same footing with respect to theoretical model assumptions. Thanks to this effort, a number of novel physics studies make use of ALPINIST. This makes this field as a whole more accessible for future ideas. Going to data-analysis, AxScale has put NA62 among the prime experiments for the study of weakly coupled particles at the MeV to GeV particles, significantly pushing the paramter space explore beyond current boundaries. W
Within RADES, thanks to AxScale, a number of experimental campaigns were performed, and analysis results have been published in parameter regions thus far untackled by other experiments, especially in the axion post-inflationary regime. RADES published the first full axion search result employing high-temperature superconductors as radiofrequency cavity coating.
In summary: the detection of an axion or similar fundamental new physics particles would be a ground-breaking discovery, shedding light on the theory beyond the Standard Model of Particle Physics. Potentially this could also be connected to solving the puzzle to understand the nature of Dark Matter. With the research conducted in AxScale, a corner-stone has been laid for a possible discovery: A plethora of data taken towards the end of the action remains to be analyzed. A novel discovery in those data would constitute a Nobel-winning breakthrough in in Particle Physics with vast implications for Cosmology and Astrophysics.

RADES cavity from first data run 2018