The CMS Particle Flow Algorithm

Milos Dordevic,V.E Volkova,V.A Rubakov,D.G Levkov,V.A Matveev,Y.V Zhezher

doi:10.1051/epjconf/201819102016

Milos Dordevic, V.E Volkova + Show 4 more

Open Access

https://doi.org/10.1051/epjconf/201819102016

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Abstract

The event reconstruction at the Compact Muon Solenoid (CMS) experiment at the CERN Large Hadron Collider (LHC) is predominantly based on the Particle Flow algorithm. This algorithm for a global event description uses the information from all subdetector systems, unlike the previous, traditional approaches that were focused on the localized information in each subdetector. These traditional methods use the raw information (tracks, hits), while the Particle Flow algorithm completely reconstructs the event by identifying and reconstructing the comprehensive list of final-state particles (photons, electrons, muons, charged and neutral hadrons), resulting in superior reconstruction of jets, missing transverse energy, tau leptons, electrons and muons. This approach also allows for efficient identification and mitigation of the pileup effect. The concept and performance of the Particle Flow algorithm, together with the prospects for its development in the context of the upgraded CMS detector, are presented in this overview.

Highlights

The traditional event reconstruction at hadron colliders implied that jets consist of hadrons and photons, having their energy measured exclusively by the calorimeters, without identification of individual particles within jets and without using the information from tracker and muon detectors
The Particle Flow (PF) algorithm [1] is based on a concept of global event reconstruction as it performs a correlation of the basic elements obtained from all subdetector systems, in order to identify all particles in the event and measure their properties
Charged hadrons are identified by linking the track to one or more calorimeter clusters, while photons and neutral hadrons are in general identified by calorimeter clusters that are not linked to the track

Summary

Introduction

The traditional event reconstruction at hadron colliders implied that jets consist of hadrons and photons, having their energy measured exclusively by the calorimeters, without identification of individual particles within jets and without using the information from tracker and muon detectors. The CMS detector is proven to be very suitable for the usage of the PF algorithm, having a high magnetic field to separate neutral from charged hadrons, fine granularity of the tracker detector for jets with transverse momenta up to 1 TeV, a highly segmented electromagnetic calorimeter (ECAL) to determine the energy fractions in jets, followed by a hermetic hadronic calorimeter (HCAL), as well as an excellent system to identify muon tracks

Reconstruction of the particle-flow elements

Particle identification and reconstruction

Performance in simulation

Performance in data and pileup mitigation

Findings

Summary and outlook