Measurement of the track impact parameters resolution with the ATLAS experiment at LHC using 2016-2018 data

This study presents the measurement of the impact parameter distributions to test the resolution of the tracks reconstructed with the ATLAS inner detector at the LHC. It has been performed using proton-proton collision data collected at $\sqrt{s} = 13$TeV between 2016 and 2018. The impact parameter is defined as the distance of closest approach of the track to the collision point. Its resolution is computed using an iterative Gaussian fit performed on the core of the impact parameters distribution. It has been observed a degradation of approximately 5% over the considered period. This degradation results from the convolution of changes in the running conditions and radiation damage, which modifies the intrinsic properties of the detector, affecting its performances. To investigate the behaviour of the resolution of the transverse impact parameter measurement in a high-density environment, the quantity has also been studied as a function of the angular separation between a track and the jet axis. A degradation of approximately 10% is observed in the proximity of the jet direction.