The Advanced Thin Ionization Calorimeter (ATIC) collaboration recently published [Nature 456, 362-365 (20 November 2008)] a claim of a four sigma excess in the electron spectrum of cosmic rays. “Electron” actually means either electron or positron since they do not measure the sign of the charge. I will present a summary of the ATIC apparatus, analysis, and result followed by a critique of the analysis concentrating on the background determination. It is possible that the background was underestimated, leading to a much-reduced statistical significance.
This is another true journal club talk since I am neither a member of the ATIC collaboration nor an expert on balloon-borne cosmic ray experiments. The talk is based on a careful reading of the papers and correspondence with the authors.
Links to the Nature paper, supplementary to the Nature paper, and other ATIC papers may be found at http://atic.phys.lsu.edu/aticweb/index.html .