Improving cosmic ray composition determination through better tracking

Several experiments now under construction or in various stages of study are intended to improve cosmic ray composition measurements through element (or element group) identification. To achieve this, some form of finely segmented (pixel) charge detector will be used to reduce the effects of back-scattered particles on the measurement. These experiments will utilize 'tracking calorimeters' to reconstruct the trajectory of high-energy cosmic particles through the charge measurement device to identify the correct pixel. As an example, the Advanced Cosmic-ray Composition Experiment on the Space Station, a mission currently being studied, is aimed at obtaining more precise measurements, above the atmosphere, of the element-by-element (H - U) fluxes of cosmic ray particles at the limiting energies expected from supernova shocks. The expected energy reach is 10(15) eV for H - Fe but less than 10(10) eV for the heavier nuclei, which do not depend on the calorimeter. The following describes a tracking algorithm based on information from the calorimeter, scintillators, and charge detector, suggests some design choices, and estimates the expected tracking resolution for this experiment. (C) 2001 COSPAR. Published by Elsevier Science Ltd. All rights reserved.