Jet reconstruction with particle flow in heavy-ion collisions with CMS

Matthew Nguyen

doi:10.1088/0954-3899/38/12/124151

Abstract

In the particle-flow approach, information from all available sub-detector systems is combined to reconstruct all stable particles. The global event reconstruction has been shown to improve, in particular, the resolution of jet energy and missing transverse energy in pp collisions compared to purely calorimetric measurements. This improvement is achieved primarily by combining the precise momentum determination of charged hadrons in the silicon tracker with the associated energy depositions in the calorimeters. By resolving individual particles inside jets, particle flow reduces the sensitivity of the jet energy scale to the jet fragmentation pattern, which is known to be one of the largest sources of systematic uncertainty in jet reconstruction. Particle flow reconstruction is thus potentially well suited for the study of potential modifications to jet fragmentation in heavy-ion collisions. The particle flow algorithm has been adapted to the heavy-ion environment. The performance of jet reconstruction from particle flow objects in Pb–Pb collisions using the anti-kT jet reconstruction algorithm is presented.

Highlights

In the particle-flow approach information from all available sub-detector systems is combined to reconstruct all stable particles
In CMS jets are clustered from calorimeter towers which consist of a single hadron calorimeter (HCAL) cell and the subtended 5x5 set of electromagnetic calorimeter (ECAL) crystals
As the tower dimensions are determined by the HCAL geometry, the ECAL granularity is not exploited in this approach

Summary

Introduction

In the particle-flow approach information from all available sub-detector systems is combined to reconstruct all stable particles. In the approach traditionally used at hadron colliders, jets are reconstructed exclusively from calorimeter information (Calo jets). The CMS implementation of PF has been shown to largely improve the jet pT and angular resolution in pp collisions [2].

Results

Conclusion