Overview of Energy Reconstruction, and Electron and Photon Performances with the CMS ECAL in Run II

Rafael Teixeira De Lima,Cms Collaboration

doi:10.1088/1742-6596/928/1/012005

Abstract

The electromagnetic calorimeter (ECAL) of the Compact Muon Solenoid (CMS) Experiment is crucial for achieving high resolution measurements of electrons and photons. Maintaining and possibly improving the excellent performance achieved in Run I is vital for measurements of the Standard Model Higgs boson and searches for new higher mass resonances in final states with electrons and photons. Since spring 2015, the ECAL has operated with proton-proton collisions at 13 TeV center-of-mass energy and at a reduced bunch spacing of 25 ns. The instantaneous luminosity delivered by the LHC during Run II is expected to exceed the levels previously attained. The average number of concurrent proton-proton collisions per bunch-crossing (pileup) is expected to reach up to 40 interactions. In this summary we present new crystal energy reconstruction algorithms and clustering techniques that have been developed to maintain the excellent performance of the CMS ECAL throughout Run II. We will show first performance results from 2015 data, achieved through energy calibrations using electrons from W and Z boson decays, photons from π0/η decays, and the azimuthally symmetric energy distribution of minimum bias events. Lastly, we present an outlook on the expected Run II performance in the next years.

Highlights

The Compact Muon Solenoid (CMS) ECAL is a high-resolution, hermetic, and homogeneous electromagnetic calorimeter made of 75,848 scintillating lead tungstate crystals divided among a barrel (|η| < 1.48) and two endcaps (1.48 < |η| < 3.0) [1]
The electromagnetic calorimeter (ECAL) of the Compact Muon Solenoid (CMS) Experiment is crucial for achieving high resolution measurements of electrons and photons
The average number of concurrent proton-proton collisions per bunchcrossing is expected to reach up to 40 interactions. In this summary we present new crystal energy reconstruction algorithms and clustering techniques that have been developed to maintain the excellent performance of the CMS ECAL throughout Run II

Summary

Introduction

The CMS ECAL is a high-resolution, hermetic, and homogeneous electromagnetic calorimeter made of 75,848 scintillating lead tungstate crystals divided among a barrel (|η| < 1.48) and two endcaps (1.48 < |η| < 3.0) [1]. The signal readout is performed with two avalanche photodiodes (APDs) per crystal in the barrel, and one vacuum phototriode (VPT) in the endcaps. These characteristics, translated into precise energy and timing resolutions, are an invaluable tool for the CMS physics program. Completing the CMS electromagnetic calorimeter system is a preshower detector (ES), based on lead absorbers equipped with silicon strip sensors It is installed in front of the ECAL endcaps, covering the region 1.65 < |η| < 2.6. In the 2015 data taking period, the CMS ECAL operated with more than 98% of its channels active, and was responsible for less than 7% of CMS downtime during physics runs

Energy Reconstruction with ECAL

Findings

Online Reconstruction