University of Maryland
Direct measurements of cosmic-ray protons - how far beyond the TeV mark can we go?
One of the most important tests for the Super Nova Remnant (SNR) model of cosmic-ray acceleration is verifying the existence of a cut off in the proton spectrum due to the expected acceleration limit, predicted to be near 100 TeV. This test requires accurate identification of cosmic-ray nuclei, a sufficiently accurate measurement of their energy, and a large enough collection power to have meaningful statistics far above 1 TeV. Only with direct measurement of nuclei at the top of the atmosphere can incident charge be measured with any accuracy, allowing elemental spectra to be reconstructed. Over the last two decades three main types of experiments have been flown at sub-orbital altitudes to perform such measurements - Transition Radiation Detectors (TRDs), Emulsion Chambers (EC) and calorimeters. Since the first of these is not practical for measuring protons at TeV energies, the talk will concentrate on the last two techniques, and use some examples (JACEE, RUNJOB, ATIC & CREAM) to compare their respective strengths and weaknesses. Finally, an assessment will be made as to how far we can expect to push the high energy frontier of these measurements with current technologies.