Shower shapes and magnetic field in the ATLAS EM calorimeter

The context of this project is the CERN summer student remote program for the year 2020. During that remote activity, I had to learn Python and Root, therefore I started to learn how to use it to draw histograms and plots. Moreover, I presented my results in the Atlas EGamma meeting two times. In the first data recorded by ATLAS in 2010, it was observed [1] that several of the shower shape variables were mis-modelled by the Monte Carlo (MC) simulation. In particular, comparing the Rη and Wη2 distributions for signal electrons from Z → ee events, significant discrepancies between data and MC simulation can be seen in Figure (1). In order to explain these discrepancies, we want to consider the influence of the residual magnetic field in the calorimeter. We also looked for how big of the magnetic effect can involve. To quantify this, we did a simple comparison between two singlephoton samples that have magnetic field either enabled or disabled. In addition, we had tested some samples with an influence of cross-talk, Birks’ law, and Geant4 simulation.