Study of the time dependence of helium nuclei flux measured by the PAMELA and GAPS experiments

Cosmic Rays (CRs) are energetic particles propagating in space and mainly originating from outside the heliosphere. They are accelerated through physical phenomena involving strong magnetic fields, like magnetic reconnections, Super Novae Remnants (SNRs), or Active Galactic Nuclei (AGN). The main components of cosmic radiation in particle number are protons and helium nuclei, with abundances of ∼ 89% and ∼ 9% respectively, and a smaller fraction of heavier elements, electrons, anti-protons, and positrons. CR propagation inside the heliosphere is driven by the solar magnetic field, embedded in the expanding solar wind constantly expelled from the Sun. The Sun undergoes a magnetic polarity reversal every 11 years, alternating a period of minimum and maximum activity. During the former, the CRs intensity measured at Earth is maximum while during the latter the situation is reversed. This phenomenon, known as solar modulation, has been studied in this work observing the induced effects on the helium component of cosmic radiation measured in the energy range 0.08 − 20 GeV/n by the PAMELA experiment; a satellite-borne detector with almost ten years of activity (June 15th 2006 - January 23rd 2016). The measured time-dependent Galactic CR helium energy spectra were then compared to the PAMELA proton data in terms of proton-to-helium ratio time profile studies to analyze any features that could result from the different masses and local interstellar spectra shapes. Time and rigidity (i.e., the particle charge over its momentum) dependencies are observed in the proton-tohelium flux ratios and the force-field approximation of the solar modulation was used to relate these dependencies to the different shapes of the local interstellar proton and helium-nuclei spectra. Moreover, a comparison of measured data with a full threedimensional cosmic-ray propagation model for describing CR modulation throughout the heliosphere is also presented. These measurements will be extended with the future GAPS experiment, a balloon-borne experiment, scheduled for a first flight in the austral summer 2022/2023. Although this experiment is designed to study low energy (< 0.25 GeV/n) anti-nuclei as a signature of Dark Matter (DM) annihilation or decay, it will also be able to conduct precision low energy nuclei measurements. In this work a proton-helium identification analysis on GAPS simulated data will be discussed, i comparing a classical approach with a modern machine learning approach.