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

Part of the early physics program at the ATLAS experiment is to measure basic properties of proton proton collisions, such as charged particle multiplicities, which will constrain phenomenological models 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 complimentary types of minimum bias triggers. A hardware based first level trigger sensitive to the forward regions of 2.2 < $|\eta|$ < 3.8 has been proved to efficiently select proton proton collisions, while an Inner Detector based trigger seeded on randomly sampled filled bunches which selects events with hits in the tracker, has provided a useful control sample. The performance and efficiency measurements of these triggers and detectors will be presented.