The LEAPS project

The project "Low Energy Avenues in Particles Searches (LEAPS)" is a project funded as a FIS2 Starting Grant of 1.3M€ by the Italian Ministero dell'Università e della Ricerca. (CUP: B53C25003020001)

The goals

The project investigates a number of new avenues in the study of light, weakly interacting particles. Namely, sub-GeV dark matter and neutrinos, from both a theoretical and experimental viewpoints. It explores four main directions.

• Measurements of the neutrino mass with the PTOLEMY project: PTOLEMY aims at measuring the neutrino mass by achieving an unprecedentedly high event rate and energy resolution. This can be done by studying the spectrum of the electrons emitted by the β-decay of atomic Tritium deposited on a graphene substrate. The LEAPS project is devoted to developing a complete theory for such a process, with the aim of systematically computing the expected energy spectrum, including all the relevant condensed matter effects. Such an achievement would constitute the theoretical backbone of the PTOLEMY project, proving the prediction to be tested against experimental data.

• Direct detection of sub-GeV dark matter with hydrogenated carbon nanostructures: Laboratory searches for dark matter particles lighter than the GeV are made challenging by the extremely small energy released to the detector via the standard elastic recoil of the dark matter off the detector's nuclei. The LEAPS project attempts at overcoming this difficulty by employing a new class of targets: hydrogenated carbon nanostructures such as graphene and nanotubes. A dark matter particle impinging on a hydrogen nucleus can, in fact, eject it from the structure. The (clean) experimental signature of such an event is thus the emission of a charged particle, which can easily be accelerated and detected. This process is extremely promising due to the very low energy threshold, and the possible directionality of carbon nanotubes, which would provide a fundamental tool for background discrimination. The project will develop the theoretical description of both the ejection probability, as well as the late-time dynamics of the emitted proton. It will also set up the experimental framework to try and realize the proposed experiment. In particular, we will study the growth and characterization of the hydrogenated nanostructures, as well as the calibration of the detector.

• Direct detection of sub-MeV dark matter and meV axions with antiferromagnets: Antiferromagnets, and especially Nickel Oxide, are potentially optimal probes to look for sub-MeV dark matter with spin-dependent interactions with the Standard Model. This is due to the accidental closeness between the propagation speed of spin fluctuations in Nickel Oxide, and the typical dark matter velocity. Moreover, since spin waves in antiferromagnets have energy gaps of the order of the meV, they might be able to probe the possible axion-electron coupling in yet unexplored values of the axion mass. The LEAPS project aims at developing the theory describing the interaction between dark matter, spin waves and electromagnetic fields. This will be done by heavily relying on effective field theory methods, with the end goal of determining realistic observables for a possible experimental implementation of this idea.

• The Migdal effect: The Migdal effect is a process where, following the release of some energy and momentum to a nucleus, one of the electrons in its vicinity gets excited or ionized. By leveraging this phenomenon, existing experimental collaborations are extending their sensitivity to models of dark matter interacting with nucleons, at masses below the traditional GeV limit. Leading experiments such as Xenon and DarkSide employ noble liquids (Xenon and Argon, respectively) as targets. Despite the relevance of the Migdal effect, a theory describing its occurence in noble liquids has never been developed. The project will fill this gap, writing down a systematic description of the interaction between dark matter, nuclei and electrons in a liquid environment with large polarizability. Such a theory can also shed light on the current mismatch between theoretical predictions and the lack of experimental evidence for the Migdal effect in liquid Xenon.