Time dependence of the flux of helium nuclei in cosmic rays measured by the PAMELA experiment between July 2006 and December 2009

TL;DR

This paper presents detailed measurements of helium nuclei fluxes in cosmic rays over several years, analyzing their time dependence and interpreting the results with advanced propagation models to understand solar modulation effects.

Contribution

It provides the first detailed time-resolved helium flux measurements from PAMELA and applies a 3D propagation model to interpret solar modulation effects.

Findings

Helium flux varies with solar activity over the studied period.

Proton-to-helium flux ratio shows rigidity-dependent features.

Model successfully reproduces observed flux time profiles.

Abstract

Precise time-dependent measurements of the Z = 2 component in the cosmic radiation provide crucial information about the propagation of charged particles through the heliosphere. The PAMELA experiment, with its long flight duration (15th June 2006 - 23rd January 2016) and the low energy threshold (80 MeV/n) is an ideal detector for cosmic ray solar modulation studies. In this paper, the helium nuclei spectra measured by the PAMELA instrument from July 2006 to December 2009 over a Carrington rotation time basis are presented. A state-of-the-art three-dimensional model for cosmic-ray propagation inside the heliosphere was used to interpret the time-dependent measured fluxes. Proton-to-helium flux ratio time profiles at various rigidities are also presented in order to study any features which could result from the different masses and local interstellar spectra shapes.