Low energy cosmic ray positron fraction explained by charge-sign dependent solar modulation

TL;DR

This paper models cosmic ray spectra, including positrons, accounting for charge-sign dependent solar modulation, explaining discrepancies in low-energy positron measurements by PAMELA and AMS-01 through solar cycle effects.

Contribution

It introduces a detailed transport model that incorporates charge-sign dependent solar modulation to explain low-energy cosmic ray spectra and positron fraction variations.

Findings

Reproduces observed cosmic ray spectra below 1 TeV.

Explains positron fraction discrepancies between PAMELA and AMS-01.

Highlights the impact of solar magnetic polarity on cosmic ray propagation.

Abstract

We compute cosmic ray (CR) nuclei, proton, antiproton, electron and positron spectra below 1 TeV at Earth by means of a detailed transport description in the galaxy and in the solar system. CR spectra below 10 GeV are strongly modified by charge-sign dependent propagation effects. These depend on the polarity of the solar magnetic field and therefore vary with the solar cycle. The puzzling discrepancy between the low-energy positron fraction measured by PAMELA and AMS-01 is then easily explained by their different data-taking epochs. We reproduce the observed spectra of CR light nuclei within the same galactic and solar-system propagation model.