Calibration of the CMS Electromagnetic Calorimeter with the EFlow Phi-Symmetry Method

The EFlow method of intercalibration of the CMS (Compact Muon Solenoid) Electromagnetic Calorimeter (ECAL) has already been developed for retroactive calculations after the data taking has been completed. It is a modification of the $\phi$-symmetry method which makes use of the symmetry of the CMS detector and the initial conditions of the proton-proton collisions in the $\phi$ direction. These imply that the results of any experiment will (with a sufficiently large sample size) be symmetrical in the $\phi$ direction. This includes the transverse energy measured at each crystal in the ECAL, to provide corrections for the energy drift. In order to be able to execute these calculations efficiently during data taking and provide corrections of the regional drift in the response of the ECAL, in particular to the radiation ageing of the PN diodes used as references for the laser calibration, the EFlow calculations are integrated into the CMS automation framework. The framework's freedom, in how data is grouped is used to optimise the eflow intercalibration maximising the precision of the calibration.