Geomagnetic Cutoff Calculations for the Interpretation of Low-rigidity Cosmic-ray Antiparticle Measurements

Low-rigidity cosmic rays and solar particles are strongly deflected by Earth's geomagnetic field and only particles above a certain geomagnetic cutoff rigidity are able to reach space-based or balloon-borne experiments. Geomagnetic cutoff calculations utilizing the PLANETOCOSMICS software with the IGRF geomagnetic field and the Tsyganenko magnetosphere models are discussed. These calculations focus on the time from 2011 to 2015 where the AMS-02 experiment on the International Space Station (ISS) was operational and are used to compare trajectories of cosmic-ray detectors on the ISS and balloon-borne experiments. A database approach was developed that allows very quick geomagnetic cutoff calculations, and thus an easy comparison of different trajectories. During the period under study time a particle-rich event that greatly perturbed the magnetic field strength on 7 March 2012 was observed and was studied in more detail from the geomagnetic cutoff perspective. All calculations put a special emphasis on antiparticles because precise measurement of their low-rigidity fluxes have the potential of revealing exotic sources like dark matter annihilations or primordial black holes. The findings underline that geomagnetic cutoff effects have to be treated as a function of particle charge, time, location, and direction.