Estimating Track Momentum Resolution in Minimum Bias Events using Simulation and K_s in sqrt(s) = 900 GeV collision data

The understanding of the transverse momentum (pT) resolution of the ATLAS Inner Detector is important for many physics analyses. A common approach to assess the agreement between full Monte Carlo simulation and data is to study well-measured particle decays. In this note, $K^0_s$ decays to two pions are used to quantify the pT resolution and scale of low momentum tracks, i.e. pT <~ 1GeV during the sqrt(s) = 900GeV run in 2009. The nominal Monte Carlo simulation is found to describe well the track pT resolution for pT > 500 MeV, while it is underestimated in both endcap regions for pT < 500 MeV. The track pT scale is globally well described by nominal Monte Carlo simulation within the statistical uncertainties.