Isotope solar modulation with the PAMELA experiment 2019

Abstract

The satellite-borne PAMELA experiment was launched on the 15th June 2006 from the Baikonur cosmodrome. Since then and until January 2016 PAMELA made high-precision measurements of the charged component of cosmic-rays over a wide energy range. Because of its long-duration operation, PAMELA represents an ideal detector for cosmic-ray solar modulation studies. The PAMELA collaboration already published time-dependent proton, helium and electron spectra as well as the positron to electron ratio over ten years of data taking. These results are fundamental to improve and refine propagation models the propagation models of cosmic rays through the heliosphere. Here, the yearly average spectra over the 23rd solar minimum (July 2006 - January 2009) until the middle of the 24rd solar maximum (December 2015) for 1H, 2H, 3He and 4He are presented. The isotopic composition was measured between 0.1 and 1.1 GeV/n using two different detector systems. These spectra show an increasing trend during the solar minimum period with a decrease as the solar maximum is approached. The time-dependent ratio of these isotopes is also presented. From a solar modulation point of view, a non constant ratio is typically caused by their different masses (related to their rigidity) and also the different shapes of the respective local interstellar spectra. Apart from these effects, it is worthwhile to look deeper for more fundamental causes related to their propagation and modulation mechanisms