Energy Flow Reconstruction

Particle Flow in ATLAS


The Sheffield group has developed a particle flow algorithm for use within ATLAS, which makes use of all detector information to optimise the measurement of hadronic objects such as jets and taus. The package, called eflowRec, is currently being studied for use within jet and met reconstruction, and was run in the 2015 data (and mc15 Monte Carlo) reconstruction processing. An improved version of the algorithm will be run in the 2016 data processing. eflowRec has been written within the athena offline framework in C++ and uses a python frontend to configure at run-time. A paper will be submitted to a journal in the coming months detailing the 2015 version of the algorithm, along with an ATLAS CONF note detailing the updates for 2016. Mark Hodgkinson is currently co-coordinator of the ATLAS JetETMiss particle flow task force.

We have also worked closely with physicists in the ATLAS Bonn group in Germany to develop techniques based on particle flow to reconstruct tau substructure. This substructure reconstruction can be used to measure the properties of the Higgs, when decaying to a di-tau state. A tau specific implementation of eflowRec was developed as one of several candidate algorithms for reconstruction of tau substructure, which can be used as input to the PANTau software developed at Bonn to perform tau decay mode classification. The tau scenario is a special case, where the well understood tau kinematics can be used to guide the charged shower subtraction procedure for a given particle flow algorithm. Details of the tau particle algorithm can be found in this recent paper accepted by EPJC - Reconstruction of Hadronic Decay Products of Tau Leptons with the ATLAS Experiment.

Sheffield was also responsible to develop the Event Data Model that will be used for both the eflowRec (developed at Sheffield) particle flow algorithm in jets and met, and the tau substructure algorithms in Run 2 of the LHC (which starts in 2015). This package is called xAODPFlow. xAODPFlow contains an object called xAOD::PFO which is a c++ class that represents the particle flow objects (which are the output of eflowRec and all tau substructure algorithms).

An internal ATLAS note detailing the eflowRec algorithm and its performance, using Athena 15.6.9.8, in tau and QCD di-jet scenarios is available. Previously we presented the performance in Athena version 12.0.6 here and as part of the ATLAS CSC excercise

This ATLAS twiki contains many details about the eflowRec particle flow algorithm to be used in jet and MET reconstruction. Relevant recent talks on eflowRec for jets and MET, and related work on tau substructure and PANTau, are given in the list below (note these are only accessible to ATLAS collaboration members):

2015

  • Details of particle flow studies during Long Shutdown One parts one and two (C. Young, CERN).

2014

2013

2012



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