Abstract
The CMS apparatus was identified, a few years before the start of the LHC operation at CERN, to feature properties well suited to particle-flow (PF) reconstruction: a highly-segmented tracker, a fine-grained electromagnetic calorimeter, a hermetic hadron calorimeter, a strong magnetic field, and an excellent muon spectrometer. A fully-fledged PF reconstruction algorithm tuned to the CMS detector was therefore developed and has been consistently used in physics analyses for the first time at a hadron collider. For each collision, the comprehensive list of final-state particles identified and reconstructed by the algorithm provides a global event description that leads to unprecedented CMS performance for jet and hadronic τ decay reconstruction, missing transverse momentum determination, and electron and muon identification. This approach also allows particles from pileup interactions to be identified and enables efficient pileup mitigation methods. The data collected by CMS at a centre-of-mass energy of 8\\TeV show excellent agreement with the simulation and confirm the superior PF performance at least up to an average of 20 pileup interactions.
Highlights
Modern general-purpose detectors at high-energy colliders are based on the concept of cylindrical detection layers, nested around the beam axis
Charged and neutral hadrons may initiate a hadronic shower in the electromagnetic calorimeter (ECAL) as well, which is subsequently fully absorbed in the hadron calorimeter (HCAL)
When it comes to evaluating the calibration parameters for actual clusters in the preshower fiducial region, ηtrue is estimated from the ECAL cluster pseudorapidity, and Etrue is approximated by a linear combination of energies measured in the ECAL (EECAL), EPS1, and EPS2, with fixed coefficients
Summary
Modern general-purpose detectors at high-energy colliders are based on the concept of cylindrical detection layers, nested around the beam axis. A significantly improved event description can be achieved by correlating the basic elements from all detector layers (tracks and clusters) to identify each final-state particle, and by combining the corresponding measurements to reconstruct the particle properties on the basis of this identification. This holistic approach is called particle-flow (PF) reconstruction.
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