Dark matter search with low energy antimatter cosmic rays

Principal Investigator: Riccardo Munini


  • Astroparticle Physics

Abstract: Since many years it has been know that antimatter can shed light on the nature of dark matter. In the recent years, this field has witnessed significant advancements both on the experimental and theoretical side. Antiprotons are a much studied channel where significantly improved statistics at low energies are expected in the next years. However, uncertainties on the secondary production of antiprotons by interaction of cosmic rays with the interstellar matter and on their propagation in the Galaxy and in the heliosphere are affecting a comprehensive understanding of their origin. Heavier cosmic-ray antinuclei such as antideuterons and antihelium are also predicted to be produced as secondaries but their spectra at low energies (below a few GeV/n) are expected to be orders of magnitude lower than those of antideuterons and antihelium produced by plausible models of dark matter annihilation or decay. We propose to study the phenomenological and experimental challenges of these measurements.

Status of project and perspectives:

Status of project: In the last two years, through the cooperation of experimental and theoretical groups fostered by the IFPU environment, it was possible to obtain many of the set goals of this project. The foremost activity was a one-week IFPU special program held in presence in November 2021. Specifically, the project successfully integrated the research methodologies it set out to develop. The combination of experimental data from different experiments and numerical models allowed a high-quality interpretation of the data. The analysis of the energy spectra of the protons of PAMELA, AMS02, and BESS-POLARII allowed the calibration of a numerical model describing the propagation of cosmic rays in the Heliosphere for various epochs of solar activity. The calibration process was performed with a multi-parameter optimization technique, developing a Markov Chain. Most importantly, this process naturally provided an estimation of the uncertainties related to each calibrated propagation parameter and thus global uncertainties on the energy spectra associated with the solar modulation. The model made it possible to reproduce the experimental data with an accuracy of a few percent. The parameters obtained for the different periods of solar activity were then used for an inverse process to estimate the best Local Interstellar Spectrum of antiprotons. The idea was to develop an independent procedure to estimate the LIS with respect to the usual approaches based on galactic propagation codes like GALPROP. Through a Markov Chain, the best spectral shape of the LIS of the antiprotons was found. It should be emphasized that this solar modulation model allows taking into account the charge-sign modulation effect and is not affected by significant (10-15%) systematic uncertainties that hinder simpler analytic models like the force field approximation. Finally, three LIS for antiprotons were obtained with a first estimation of uncertainties.

Collaboration and meetings: This project benefits from the exchange of information with other groups facilitated by an institute like IFPU. The one-week IFPU workshop was of great importance for the exchange of ideas and different points of view on the same problem.

Perspectives: The group will continue to improve the study of systematic uncertainties on the antiproton LIS including those related to the experimental measurements. This is a different from the approaches used by other groups but allows for a comprehensive study of the experimental uncertainties of the various data sets. Finally, the comparison of the estimated antiproton LIS with theoretical prediction will allow competitive interpretation of the data in search of possible signal of new physics. Additionally, prediction on heavier antinuclei species, e.g. antideuterons and antihelium nuclei, will be drawn in anticipation of forthcoming experimental results.