Performance of the ATLAS Inner Detector Track and Vertex Reconstruction in the High Pile-Up LHC Environment

The performance of the ATLAS inner detector in a high occupancy environment of approximately 30 inelastic proton-proton interactions per bunch crossing is presented. The track and vertex reconstruction algorithms are studied in data by comparing track and vertex properties such as multiplicities, track impact parameters, the number of hits on track and detector occupancies for a varying number of proton-proton interactions per bunch crossing. Several simulated samples are used to estimate the track and vertex reconstruction efficiency and to quantify the level of agreement between data and simulation. It is shown that although pile-up has a significant impact in many areas, the detector design and reconstruction algorithms are sufficiently robust to maintain a good performance in such a high pile-up environment.