Reconstruction of signal amplitudes in the CMS electromagnetic calorimeter in the presence of overlapping proton-proton interactions

TL;DR

This paper introduces a new template fitting method for reconstructing signal amplitudes in the CMS electromagnetic calorimeter, effectively reducing pileup effects and improving energy resolution during high-luminosity LHC operations.

Contribution

A novel, fast template fitting technique for signal amplitude reconstruction that suppresses pileup effects in the CMS electromagnetic calorimeter during Run 2.

Findings

Significant improvement in energy resolution across a wide energy range.

Effective suppression of out-of-time pileup contributions.

Method is suitable for real-time trigger and offline reconstruction.

Abstract

A template fitting technique for reconstructing the amplitude of signals produced by the lead tungstate crystals of the CMS electromagnetic calorimeter is described. This novel approach is designed to suppress the increased out-of-time pileup contribution to the signal following the reduction of the accelerator bunch spacing from 50 to 25 ns at the start of Run 2 of the LHC. Execution of the algorithm is sufficiently fast for it to be employed in the CMS high-level trigger. It is also used in the offline event reconstruction. Results obtained from simulations and from Run 2 collision data (2015-2018) demonstrate a substantial improvement in the energy resolution of the calorimeter over a range of energies extending from a few GeV to several tens of GeV.