Measurement of the CMS ECAL Performance with Z Dielectron Decay Events in 2012 Data

The detection and measurements of the decay mode of the Higgs boson into two photons for the Compact Muon Solenoid experiment (CMS) is crucially dependent on the energy resolution of the Electromagnetic Calorimeter (ECAL) as the energy resolution of the detector dominates the mass resolution of the decay channel. The mass resolution of the ECAL detector is measured by reconstructing the Z peak from its decay channel into two electrons with an optimization of electron ID selections and measuring the width of the peak by fitting it with a convolution of BreitWigner and CrystalBall functions. We measure the mass resolution of the CMS ECAL with Z dielectron decays in 2012 Data and Monte Carlo and discuss potential reasons for discrepancies between Data and Monte Carlo performance, such as regression corrections, MC shower simulation, detector calibration, laser correction from the detector monitoring system and increased pile up.