Energy spectra of H and He from the ATIC-2 experiment
The Advanced Thin Ionization Calorimeter (ATIC) experiment measures the energy spectra of individual elements, from H to Fe, in the energy region from about 100 GeV to tens of TeV. ATIC was flown twice on long-duration balloon flights around the South Pole, 12/00-1/01 (ATIC-1), and 12/02-1/03 (ATIC-2). En-ergy deposit spectra for H and He from both flights are presented. The data from ATIC-2 (18 days) show superior resolution and preliminary analysis indicates evolving energy spectra (i.e. becoming harder with increasing energy) consistent with changes expected from propagation models. The data also suggest a slightly steeper source spectrum for H than for He.