Combined Intercalibration and Longitudinal Weight Extraction for the ATLAS Liquid-Argon EM Calorimeter

Two major problems for most physics analyses in ATLAS are: (i) the equalization of response of different physical regions of the electromagnetic (EM) Calorimeter (intercalibration), and (ii) the correction of upstream material effects in energy reconstruction through extraction of the EM longitudinal weights. A possible solution to these problems consists of the in-situ calibration of the calorimeter using electrons from W$^\pm$ or Z$^0$-boson decays. When electrons are used, intercalibration depends on longitudinal weights and vice versa, making it very hard to decouple the two effects in-situ. In this note we report on the development of a combined minimization method that provides simultaneous intercalibration and longitudinal weight extraction and can be used during the ATLAS data taking. It is shown that an intercalibration at the $\simeq$2ppm level, including upstream material effects and excluding the crack region, can be achieved under realistic conditions. A small degradation of the energy resolution is seen. One advantage of the combined method is the use of a single data sample. In this study event samples from the Data Challenge 2 (DC2) production were used to test the applicability of the method.