Performance of the ATLAS Secondary Vertex b-tagging Algorithm in 900 GeV Collision Data

In December 2009, the ATLAS experiment recorded approximately 400,000 collision events, at a centre-of-mass energy of 900 GeV, with the tracking detectors and the solenoid magnet fully operational. This note describes performance studies of a secondary vertex b-tagging algorithm using collision data. The analysis is based on approximately 10,000 jets with pseudorapidity |$\eta$| < 2.5. As very few jets are expected to be tagged as b-jet candidates using the standard algorithm configuration, track selection criteria have been loosened to allow for more light-flavour jets to be tagged. In particular, the veto of tracks consistent with coming from decays of $K^0_s$ mesons, $\Lambda^0$ baryons, photon conversions and hadronic interactions has been removed. With these looser selections, 70 secondary vertices with a positive decay length significance are reconstructed, and the vast majority of them are consistent with originating from decays of $K^0_s$ mesons. The rate of reconstructed secondary vertices is consistent with expectations from simulated events, as are the properties of these vertices.