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Because of the large phase space of the LAT and its complex structure, an advanced MonteCarlo simulation of the LAT, based on the Geant4 package, is used to optimize the instrument response functions and the background rejection. Testing the instrument with real beams at accelerator facilities was needed to make sure that this simulation is able to reproduce real data.
Between July and September 2006, we have tested the LAT Calibration Unit (CU) at CERN, both at PS and SPS accelerators. The CU is a detector built with two complete flight spare modules, a third spare calorimeter module, five anticoincidence tiles located around the telescope and flight-like readout electronics. The CU was exposed to gamma beams (from ~50 MeV up to 2.5 GeV) and electron beams (from 2 GeV up to 280 GeV) in many configurations (various incoming angles and impact points) in order to cover the large phase space of the LAT.
This large amount of data will allow us to determine the performances of the LAT, such as PSF and energy resolution. This poster will present the preliminary results on these topics.
Heavy ion beam
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tests for the preparation of the LAT
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on-orbit calibration
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DRAFT SUBMITTED Speaker TBD on behalf of the Beam Test Team (poster)
The calorimeter (CAL) and the AntiCoincidence Detector (ACD) of the GLAST LAT telescope will be calibrated in flight with cosmic-ray heavy ions. A dedicated high level threshold in the ACD will trigger heavy ion events, and the pulse amplitude in the CAL and the ACD will be used to identify different ion species and calibrate the readout electronics. Tracker (TKR) information will be used to precisely identify the impact point and the path length of the ions in the plastic scintillators of the ACD and the CsI logs of the CAL. Such mode of operation was successfully tested in a heavy ion beam test carried out on the LAT Calibration Unit (CU) with Carbon and Xenon ions from the GSI synchrotron. The CU is a detector built with two complete flight spare modules, a third calorimeter and 5 ACD tiles which underwent a major beam test campaign in 2006 to validate the LAT MonteCarlo simulation with different particle beams.
The behaviour of all the three subsystems (TKR, CAL, ACD) under heavy ion irradiation is discussed in this poster, showing very good agreement with measurements performed on the CAL response in previous beam tests and providing as well as the results that provide the necessary input for the optimization of the strategy for on-orbit calibration.