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. Particularly interesting are the very rare cosmic-ray components of antideuterons and antihelium. These particles are expected to be produced as secondary by interaction of cosmic rays with the interstellar matter 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.

Description: Cosmic rays (CRs) are a sample of solar, galactic, and extragalactic matter that include all known nuclei, electrons and antiparticles. Their origin, acceleration mechanisms, and subsequent propagation have intrigued scientists since their discovery. What are the sources of CRs? How do they propagate toward Earth? What is the nature of dark matter (DM) and does it contribute to CRs? CRs, up to about 10^15 eV, are considered to be of galactic origin, and diffusive shock acceleration at supernova remnants emerges as an ideal mechanism to supply their accelerations. Once accelerated, CRs diffuse under the influence of the local magnetic field undergoing energy losses and hadronic interactions with the interstellar matter. Subsequently, CRs are affected by the solar wind when entering the heliosphere. Below tens of GeV solar activity significantly suppress and modulate the galactic CR spectrum with respect to the Local Interstellar Spectrum (LIS) which is the CR intensity outside the heliosphere. Antiparticles are a secondary component of CRs, being produced in the interaction between primary CRs and the interstellar matter. Particularly intriguing is the possibility to extract from the abundances of antiparticles in CR information about novel sources of either astrophysical or particle physics origin. Indeed, since many years, it has been know that antimatter can shed light on the nature of DM. Many beyond the Standard Model theories, such as supersymmetry and extra dimensions, provide excellent weakly interacting massive particle (WIMP) candidates for DM. Such particles could self annihilate or decay producing a signal of ordinary matter in CRs. So far, it has been impossible to identify conclusively a DM signature in CRs due to uncertain astrophysical backgrounds. Numerical codes are used to estimate the anti-matter amount in CRs. These codes simulate the production and the propagation of CRs through the Galaxy and provide a LIS with its associated uncertainties. Moreover, since the measurements are made inside the Heliosphere, the solar modulation, which is a time dependent effect following the 11 year solar activity, has to take into account and has to be properly modeled since it has a significant effect and introduce additional uncertainties. Antiproton could be used as a probe for dark matter annihilation but the expected signal is only a fraction (10-30%) of the secondary cosmic rays. Nevertheless astrophysical backgrounds complicate a clear identification of DM from indirect searches, a few signals could yield potentially unambiguous results. These are very rare components of the CRs such as antideuterons (anti2H) and antihelium (antiHe). These particles are expected to be produced as secondaries but their spectra below a few GeV/n are estimated to be orders of magnitude lower than those produced by plausible models of DM annihilation or decay. However these particle energy spectra are significantly affected by the solar modulation. The solar modulation is usually modeled with the force field approximation (FFA), an approach which solves with huge approximations the equation that describes the propagation of energetic charged particles inside the Heliosphere (Parker equation). This simplified approach works for periods of minimum solar activity and a limited range of energy. In this proposal we plan to compare various model for secondary antimatter cosmic rays production and estimate the related sources of uncertainties due to production cross section and propagation through the galaxy and Heliosphere. The expected signal from dark matter annihilation from different models will be then combined with this signal obtaining the expected amount of antiparticles in various channel. This expectation will be compared with existing experimental data (PAMELA, BESS, AMS02) taken in different epoch of solar modulation, and with future data from the GAPS experiment. IFPU is the perfect place to carry out this activity since it provides a location where the local theoretical and experimental groups with expertise in this field of research can come together. Additionally, we plan to organize at least one workshop at the Institute along with more frequent meetings of local and Italian groups.