ALBERT

Description: The ATIC balloon-born experiment measures the energy spectra of elements from H to Fe in primary cosmic rays from about 100 GeV to 100 TeV. ATIC is comprised of a fully active bismuth germinate calorimeter, a carbon target with embedded scintillator hodoscopes, and a silicon matrix that is used as a main charge detector. The silicon matrix produces good charge resolution for the protons and helium but only a partial resolution for heavier nuclei. In the present paper a charge resolution of ATIC device was improved and backgrounds were reduced in the region from Be to Si by means of the upper layer of the scintillator hodoscope that was used as charge detector together with silicon matrix. Relative fluxes of nuclei B, C, N, O in the energy region from about 20 GeV/nucleon to 200 GeV/nucleon that were obtained from new high-resolution and high-quality charge spectra of nuclei are presented.

Description: The Advanced Thin Ionization Calorimeter (ATIC) long duration balloon experiment had a successful science flight accumulating 18 days of data (12/02 - 1/03) during a single circumnavigation in Antarctica. ATIC measures the energy spectra of elements from H to Fe in primary cosmic rays using a fully active Bismuth Germanate calorimeter preceded by a carbon target, with embedded scintillator hodoscopes, and a silicon matrix charge detector at the top. Preliminary results from ATIC have been reported in previous conferences. The revised results reported here are derived from a new analysis of the data with improved charge resolution, lower background and revised energy calibration. The raw energy deposit spectra are de-convolved into primary energy spectra and extrapolated to the top of the atmosphere. We compare these revised results to previous data and comment upon the astrophysical interpretation of the results.

Description: The Advanced Thin Ionization Calorimeter (ATIC) experiment measures the energy spectra of elements, from H to Fe, in the energy region from about 100 GeV to tens of TeV. The ATIC instrument was flown twice in long-duration balloon flights around the South Pole; the ATIC-1 test flight during Dec. 2000 - Jan. 2001 and the ATIC-2 science flight during Dec. 2002 - Jan. 2003. Analyses of both datasets have, to date, relied upon the highly segmented Silicon Matrix (SiM) detector to separate the incident cosmic ray from the calorimeter backscatter and to identify the charge. This method has worked well, enabling ATIC to separate protons from helium and to resolve all the major species up through iron. This charge resolution can be significantly improved by restricting the analysis to particle trajectories that pass through two SiM pixels at the cost of using only a fraction of the potential instrument geometry. However, immediately below the SiM is the two layer SI hodoscope (x, y) consisting of Bicron BC-408 plastic scintillator 2 cm wide, 1 cm thick, 88.2 cm long strips viewed by Hamamatsu R5611 photomultiplier tubes on each end of each strip. The primary purpose of the ATIC hodoscopes is to provide a fast trigger, and each hodoscope includes two crossed layers of strips (42 per layer in the case of Sl) providing supplemental particle trajectory information. The hodoscope readout electronics were designed to provide reasonable charge resolution over the dynamic range from protons through iron. This presentation discusses the S 1 hodoscope energy deposit calibrations, examines the charge resolution possible with this detector and investigates combining the S1 and SiM charge measurements to improve the overall ATIC charge resolution while minimizing degradation of the instrument geometry.