Measuring Low-Energy Electron and Positron Flux with the Upcoming AESOP-Lite Mission

In May 2018, the balloon-borne spectrometer AESOP-Lite (Anti-Electron Sub-Orbital Payload Low Energy) observed the electron and positron flux at energies between 20MeV and 1GeV during its flight from Kiruna, Sweden to Ellesmere Island, Canada. AESOP-Lite is set to launch again from McMurdo Station in Antarctica this upcoming winter. We expect an improvement over the 2018 measurements due to two factors: the location of the flight, and an increased balloon size. The electron rigidity cutoff is essentially zero at the launch site, so the growth curves measured during the ascent will not be contaminated by re-entrant splash albedo, resulting in a better estimate of the primary background that consists of secondary electrons produced by the interaction of the galactic cosmic ray nuclei in the atmosphere. AESOP-Lite will be flown on a 60 million cubic foot volume balloon, which is expected to reach a greater altitude than the 2018 mission (~155kft vs ~140kft). The flux contribution from secondary electrons is expected to decrease and the contribution from primary electrons is expected to increase as altitude increases, leading to a better signal to background ratio. The growth curves measured in 2018 were used to estimate how this ratio will change at greater altitudes for different energy bins. We also present a novel method of estimating the geomagnetic rigidity cutoff observed by AESOP-Lite during its flight by estimating the flux contributions from the different electron flux sources in the atmosphere.