Studies for the Development of a Minimum Bias Trigger at Low Luminosities in the ATLAS-Experiment at the Large Hadron Collider

The large hadron collider LHC is a proton-proton collider at CERN and will reach a center of mass energy of sqrt(s) = 14 TeV and a luminosity of L = 1034 cm-2s-1. This enables to search for the undiscovered Higgs particle predicted by the standard model and responsible for mass creation of the elementary particles. At these high energies new particles with masses up to 5-6 TeV can be created. For these processes a high momentum transfer Q2 is involved. However, in most of the cases in proton-proton collisions, up to 107 􀀀 108 times for certain processes, soft interactions take place where only a small momentum is transferred. These events are usually called minimum bias events. As more than 20 of these minimum bias events will overlap in the detector at high luminosity they will form pile-up. Their event topology must be precisely understood in order to identify the rare physics processes of high Q2. However, the physics of low Q2-processes is only insufficiently understood. Thus, the strategy of ATLAS, one of the major experiments at LHC, is to study these events at low luminosity of L = 1031 cm-2s-1 in order to obtain a clean signal of single minimum bias events. In the present work a concept for a minimum bias trigger is outlined as well as feasibility studies for the realization of the trigger. A random event selection will be employed at the first trigger level. On higher trigger levels possible background sources have to be rejected efficiently. Main background sources that are expected to arise from empty bunch-crossing and beam-gas events. Their rejection was studied in detail and is outlined together with the results. Furthermore, timing measurements have been performed in order to test if the trigger constraints can be met. The results as well as an outlook to the implementation of such a trigger are discussed.