Preliminary results from the GLAST silicon tracker beam test

The Large Area Telescope (LAT) on board the Gamma-ray Large Area Space Telescope (GLAST) is a pair-conversion gamma-ray detector designed to explore the gamma-ray universe in the 20 MeV–300 GeV energy band. The Tracker subsystem of the LAT will perform tracking of electrons and positrons to determine the origin of the gamma-ray. The LAT instrument, the Calibration Unit (CU) and the beamtest performed at CERN during the summer 2006 are described in this paper.