Particle Flow Jets and MET Integration

Complete: 1

Structured Offline Guide common to all pages in this guide


One of the primary motivations for the Particle Flow Group is to provide a list of Particles to be used as input for Jet Reconstruction and MET Determination. Very roughly speaking, jets are composed of 65% charged hadrons (dominated by resolution and efficiency of the tracker), 20% electromagnetic particles (dominated by resolution of ECAL), 10% stable neutral hadrons (dominated by resolution of HCAL), and 5% unstable neutral hadrons (dominated by resolution and efficiency in tracker). Hence, by using the best information from each detector (tracker, ECAL, HCAL, muon system), significant improvements are expected for both the Jet Energy Resolution and Scale Uncertainty, with respect to calorimeter-only based jets.

Up to now, Particle Flow has been developed and optimsed in the context of single- and three-prong taus. Further, because Particle Flow is still relatively young, the development of Particle Flow code continues at a rapid pace. Hence, many essential ingredients are missing. The goal of this group is to optimise and contribute to the Particle Flow algorithms so they are suitable for Jet and MET Reconstruction.


  • Nuclear Interactions in the Tracker
  • Nuclear Interactions in ECAL
  • Tracking Efficiency inside the core of Jets
  • Tracking Efficiency for very low pt tracks
  • Tracking Fake Rate
  • Linking Algorithm in a high density environment
  • Neutral Energy determination

Missing Components in CMSSW

  • Navigation tool across calorimeter detector boundaries
  • Improved HCAL rec-hit navigation in the endcaps

Improvements and Missing Components needed in Particle Flow

  • Particle Flow not yet available in Endcaps
  • Optimized definition of "good quality" tracks (started)
  • Improved tracking efficiency while keeping the fake rate low (started)
  • Improved PF-Cluster linking algorithms:
    • Recover Nuclear Interactions originating in ECAL (started)
    • Optimise for high density environment
  • Inclusion of ID algorithim for Nuclear Interaction in Tracker (started)
  • Reconstruction of secondary tracks from Nuclear Interactions (started)
  • Clustering in PS (started)
  • Clustering in HF


  • A specific tutorial for Jets will appear here soon. In the mean time, the standard Particle Flow Tutorial is an excellent way to start.
  • The Fast Simulation Fast Simulation (and corresponding instructions) is also a very valuable way to start understanding and optimising the Particle Flow algorithms

Data Formats definition

RECO/AOD collection

Algorithms and Software Architecture

Analysis and Validation



  • this section can replace the titles above with links to the subgroup pages which follow the format of this page, if needed

Related Topics

Title SandBox

Area in free format for items that the groups wish to add: meetings, to do lists, links etc

Review status

Reviewer/Editor and Date (copy from screen) Comments
Main.cavana - 11 July 2007 created page

Responsible: ResponsibleIndividual
Last reviewed by: Most recent reviewer

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Topic revision: r4 - 2007-09-25 - JennyWilliams
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