CMS ECAL monitoring and calibration in LHC Run II

Tanmay Mudholkar

doi:10.1088/1742-6596/1162/1/012002

Abstract

The CMS electromagnetic calorimeter (ECAL) plays a crucial role in measurements of electrons and photons produced in LHC collisions at CMS. LHC continues to operate a highly successful data-taking program, having already delivered an integrated luminosity of more than 125 fb−1 with pp collisions since the beginning of Run II. With the expected degradation of ECAL crystals and electronics due to aging and radiation damage, it is essential to regularly fine-tune ECAL calibration factors at the highest possible granularity in order to maintain excellent energy resolution. In addition, it is important to maintain a continuous program of monitoring various physics quantities that depend on ECAL measurements, in order to validate the calibrations and ensure long-term reliability of the measurements. We describe the three techniques currently used to set the calibration factors at the crystal level: using the known energy scales in π0 → γγ and in Z → ee events, and comparing the energy measured by ECAL with an independent measurement of electron momentum from the Si tracker. We also describe the various physics quantities we monitor to validate the energy scale and shower shapes. Finally we provide an estimate of the improvement in the energy resolution after applying updated calibrations.

Highlights

The electromagnetic calorimeter (ECAL) of CMS [1] consists of a cylindrical section surrounding the central beam-pipe in the pseudorapidity range |η| < 1.48, and endcaps at both ends that extend the pseudorapidity coverage to |η| < 3.0.The primary building-blocks of ECAL are scintillating lead tungstate crystals of which there are 61,200 in the barrel and 14,648 across both endcaps
The CMS electromagnetic calorimeter (ECAL) plays a crucial role in measurements of electrons and photons produced in LHC collisions at CMS
With the expected degradation of ECAL crystals and electronics due to aging and radiation damage, it is essential to regularly fine-tune ECAL calibration factors at the highest possible granularity in order to maintain excellent energy resolution

Summary

Introduction

The electromagnetic calorimeter (ECAL) of CMS [1] consists of a cylindrical section surrounding the central beam-pipe in the pseudorapidity range |η| < 1.48, and endcaps at both ends that extend the pseudorapidity coverage to |η| < 3.0.The primary building-blocks of ECAL are scintillating lead tungstate crystals of which there are 61,200 in the barrel and 14,648 across both endcaps. We describe the three techniques currently used to set the calibration factors at the crystal level: using the known energy scales in π0 → γγ and in Z → ee events, and comparing the energy measured by ECAL with an independent measurement of electron momentum from the Si tracker.

Results

Conclusion