Test and study of the barrel pre-sampler of the Atlas detector

This study was made in the framework of the construction of the barrel pre-sampler which will equip the front face of the ATLAS electromagnetic calorimeter. The pre sampler 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 pre-sampler components. Two pre-sampler sectors (1/32 of the detector) have been constructed in their final version by the ATLAS pre-sampler 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 test pulse, 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. Test beam data analysis, compared to Monte Carlo simulations, have shown that the pre-sampler performs its role correctly. Energy resolution as a function of the amount of upstream material, linearity and uniformity have been measured for the pre-sampler plus electromagnetic calorimeter system. (author)