Contributing to shed light on dark matter and the matter-antimatter asymmetry in the Universe
Multiple and concurring evidences reveal that the vast majority of the matter content of the universe is non baryonic and electrically neutral. This component is usually called Dark Matter (DM), for its lack of electromagnetic interactions, and is measured to constitute 25% of the content of the Universe. The Dark Matter origin and nature is one of the most intriguing puzzle still unresolved, however the most common hypothesis is that it consists of weakly interacting massive particles (WIMPs), supposed to be cold thermal relics of the Big-Bang.
The indirect detection of DM is based on the search of the products of DM annihilation or decay. They should appear as distortions in the gamma rays spectra and or in anomalies in the rare Cosmic Ray (CR) components. In particular antimatter components, like antiprotons, antideuterons and positrons, promise to provide sensitivity to DM annihilation on the top of the standard astrophysical production.
The galactic cosmic rays span an energy range from about tens of MeV up to hundreds of TeV, and include nuclei from proton to iron and nickel, antiprotons, leptons and gamma-rays. The interpretation of galactic cosmic ray data requires, as well as the correct modelling of their sources and of the turbulence spectrum of the galactic magnetic field, also the knowledge of the cross sections that regulate the production and destruction of cosmic rays interacting with the interstellar medium.
For many production and inelastic cross sections, data are scarce or definitely missing. In particular, the antiprotons in the Galaxy are of secondary origin and produced by the scattering of cosmic proton and helium nuclei off the hydrogen and helium in the interstellar medium. The empirical modelling of those cross sections induces an uncertainty in the antiproton flux of about 15-20%. This should be compared with the < 4% accuracy of the AMS-02 high-precision data on the antiproton flux in the rigidity range 1 GV to 100 GV.
The AMBER physics program at CERN aims at advancing our understanding of antiproton production processes relevant to cosmic ray physics. In 2023, AMBER conducted an extensive measurement of the antiproton production cross-section using a proton beam incident on a helium (⁴He) target. This provided novel data for the reaction p+⁴He→p̄+X, covering an unprecedented momentum range from 60 to 250 GeV/c, crucial for modeling cosmic antiproton fluxes.
In 2024, the physics program further expanded, exploring proton-proton (p+p) and proton-deuterium (p+D) collisions at beam momenta of 80, 160, and 250 GeV/c. Using liquid hydrogen and deuterium targets, these measurements specifically targeted the investigation of potential isospin asymmetry effects in the production of antiprotons compared to antineutrons.
Both data-taking phases employed a consistent spectrometer setup, leveraging a newly developed target system prepared in collaboration with CERN's TE-CRG group.
Currently, AMBER is in the data analysis phase, evaluating the collected datasets to reduce uncertainties in cosmic ray interaction models and deepen our understanding of cosmic antiproton sources.