Abstract : This study was made in the framework of the construction of the barrel presampler which will equip the front face of the ATLAS electromagnetic calorimeter. The presampler consists of a thin active layer of 11 mm liquid argon. Its purpose is to take into account the energy loss of particles in the upstream material.
A series of tests has been elaborated in order to check different presampler components. Two presampler sectors (1/32 of the detector) have been constructed in their final version by the ATLAS-presampler collaboration and assembled at ISN in Grenoble, where they were tested at room and liquid nitrogen temperatures rising a dedicated test bench. The performances : high voltage behaviour, electronic. response to a testpulse, noise of the detection cells, cross-talk, etc... satisfy the requirements. Then, these two sectors were mounted at CERN in front of one electromagnetic calorimeter module and tested in a beam in 1998 and 1999. Testbeam data analysis, compared to Monte Carlo simulations, have shown that the presampler performs its role correctly. Energy resolution as a function of the amount of upstrcam material, linearity and uniformity have been measured for the presampler plus electromagnetic calorimeter system.