Prospects for Measuring the Positron Excess with the Cherenkov Telescope Array

TL;DR

This paper explores the potential of the Cherenkov Telescope Array (CTA) to measure the positron excess in cosmic rays at higher energies using moon shadow observations, which could help distinguish between different astrophysical and dark matter scenarios.

Contribution

It presents simulated estimates of CTA's capabilities to measure the positron fraction via moon shadow observations, highlighting its unprecedented sensitivity and potential improvements with silicon photomultipliers.

Findings

CTA could successfully measure the positron fraction at higher energies.

Silicon photomultipliers may enhance observation feasibility near the moon.

Simulations indicate promising prospects for discriminating cosmic ray sources.

Abstract

The excess of positrons in cosmic rays above $\sim$10 GeV has been a puzzle since it was discovered. Possible interpretations of the excess have been suggested, including acceleration in a local supernova remnant or annihilation of dark matter particles. To discriminate between these scenarios, the positron fraction must be measured at higher energies. One technique to perform this measurement is using the Earth-Moon spectrometer: observing the deflection of positron and electron moon shadows by the Earth's magnetic field. The measurement has been attempted by previous imaging atmospheric Cherenkov telescopes without success. The Cherenkov Telescope Array (CTA) will have unprecedented sensitivity and background rejection that could make this measurement successful for the first time. In addition, the possibility of using silicon photomultipliers in some of the CTA telescopes could greatly increase the feasibility of making observations near the moon. Estimates of the capabilities of CTA to measure the positron fraction using simulated observations of the moon shadow will be presented.