Performance of the ATLAS Minimum Bias Trigger in pp collisions at the LHC

The early physics program at the ATLAS experiment includes measuring the basic properties of proton proton collisions, such as charged particle multiplicities, in order to constrain phenomenological models of soft interactions in the LHC energy regime. An inclusive and well understood trigger is crucial to minimize any possible bias in the event selection. The ATLAS experiment uses two complementary types of minimum bias triggers. A scintillator trigger sensitive to the forward regions of 2.1<|eta|<3.8 has been proven to efficiently select proton proton collisions, while a trigger based on counting hits in the inner tracking detector has provided a useful control sample. The performance and efficiency measurements of these triggers and detectors will be presented.