Centrality package

  • Developed in Reconstruction/HeavyIonRec/HIGlobal, it consists of:
  • HICentralityCalibrations.root file with centrality calibration histograms available via COOL reference
  • HICentralityCalibration algorithm creating file with calibration histograms after running on ESD data
  • HICentralityData class which stores per event info on centrality bin and information about percentage schema used
  • HICentrality algorithm calculating centrality bin, creating HICentralityData object and registering it with StoreGate
  • PrintHICentralityData algorithm used for monitoring/printing HICentralityData as well as example of usage
  • HICentrality algorithm is run by default in HIRecExample
  • HICentralityValidation validation algorithm exeamining and histogramming event centrality properties
  • DumpCentralityObject.py is an example of use of PrintHICentralityData
  • PrintHICentralityData algorithm is an example of use of HICentralityData

Method description

For determinantion of centrality I am currently using distribution of energy measured from calorimeters cells and distributions of number of clusters in ID silicon detectors without any cuts for the moment. The calibration has been obtained on Hijing minimum bias sample and is provided as a set of histograms with full distributions of total energy and a histogram storing Et limits at 100x1% cut bins of the cross section. The centrality bin is calculated by finding for the given event the energy bin where the current energy value fits. It is also possible to recalculate centrality bin in a coarser schema with e.g. 5 bin cuts each say 20% of the cross section. Same is also provided for other centrality measures, like the number of silicon clusters and Glauber centrality parameters, like impact parameter, number of nn collisions, number of wounded nucleons.


HICentrality algorithm is run by default in HIRecExample heavy ion reconstruction configuration and if doHIGlobalVars is turned on. It needs to read the calibration file which is defined by a tag reference in COOL database specified in HIRecExample/share/HICalibrationsCoolFolders.py. In this algorithm the HICentralityData object is created and registered with StoreGate under the name of HICentrality. The centrality bins are calculated with 100x1% precision and a default 10x10% schema is recorded in centrality object. If one wants to use a different schema during the run of HICentrality one can redefine it from python script by using property named CentralityPercSchema. Once the HICentralityObject is recorded with StoreGate it is not possible to redefine its percentage schema since it can be only obtained with const pointer. The only way then to obtain centrality bin in a different schema is to create a non-const copy of the HICentralityData object and reset the schema there. An example of this procedure is shown in PrintHICentralityData algorithm, which can be used for examining centrality object as it is shown in DumpCentralityObject.py script example.


The package has been modified to use calibration reference from COOL database available in HIGlobal-00-02-05 (fixed) and later.

Calibration files and later tags

  • Files available in HIGlobal/data
  • HICentralityCalibrations.tid19226.8671ev.root - rel 13 Hijing 5.5 TeV calibration
  • HICentralityCalibrations.tid0667320.9500ev.root - rel. 14 Hijing 5.5 TeV calibration (strongly biased)

  • Tags available in /GLOBAL/HeavyIon/CentralityCalib
  • CentralityCalib_tag1 - pointing to copy of rel. 14 Hijing 5.5 TeV calibration (strongly biased)
  • GlobalHICentralityCalib-tag1-00 - rel. 15 Hijijng 2.75 TeV calibration (available starting DBRelease-10.9.1, referred by default starting from HIRecExample-00-06-02)

-- AndrzejOlszewski - 15 June 2010

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Topic revision: r3 - 2010-06-15 - AndrzejOlszewski
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