International School of Cosmic Ray Astrophysics

14^th  Course: "Neutrinos and Explosive Events in the Universe"

A NATO Advanced Study Institute

 2-13 July 2004
Ettore Majorana Centre
Erice, Sicily, Italy

Topic: Results from the ATIC Project
Lecturer: John Wefel

The Advanced Thin Ionization Calorimeter (ATIC) experiment is a new investigation designed to measure the charge composition and energy spectra of cosmic rays in the VHE region, up to ~10¹⁴ eV per particle. The instrument is built around a fully active, Bismuth Germanate (BGO) ionization calorimeter to measure the energy deposited by cascades formed by particles interacting in a thick carbon target. A highly segmented silicon matrix, located above the target, provides good incident charge resolution plus rejection of "backscattered" particles from the cascade. Trajectory reconstruction is based on the cascade profile in the BGO calorimeter, plus information from the three pairs of scintillator hodoscope layers in the target section above it.  A full evaluation of the experiment was performed during a test flight occurring between 28 December 2000 and 13 January 2001 where ATIC was carried to an altitude of ~37 km above Antarctica by a ~850,000 m³ helium filled balloon for one circumnavigation of the continent.  ATIC returned to Antarctica in 2002-2003 for its first science flight which was launched on 29 December 2002 and achieved a flight duration of 19.75 days.  The preliminary ATIC results will be presented for both nuclei and electrons and compared to previous data.