Fast Simulation: How to tune Iterative Tracking

The seeding step is emulated by applying cuts to the SimTracks. Those cuts are tuned such to reproduce the FullSim efficiency of highPurity tracks in ttbar events, with the further constraint of trying to keep the timing as low as possible.

Note: in the past (CMSSW releases before 4_2_X) it was considered sufficient to reproduce the overall efficiency of the final track collection, allowing intermediate steps to be in disagreement with FullSim if this helped to keep timing low. Recently, however, other modules started to use a sub-set of the iterations (examples are the gsfElectron seeds, and the tracking for Particle Flow used at HLT level) and therefore it is needed to get a fair agreement step by step.

What to tune

The configurations for the individual steps are in the directory /CMSSW/FastSimulation/Tracking/python/
The list of the iterations currently in use is in FastSimulation/Tracking/python/IterativeTracking_cff.py.

Beware: there are additional cuts hardcoded in FastSimulation/Tracking/src/TrackerRecHit.cc

Instructions

Produce relval-like ttbar events and DQM histograms from them:

cmsDriver.py TTbar_Tauola_7TeV_cfi.py -s GEN,FASTSIM,HLT,VALIDATION --pileup=NoPileUp --conditions auto:mc --eventcontent=FEVTDEBUGHLT --datatier GEN-SIM-DIGI-RECO -n 10
cmsDriver.py step3 -s HARVESTING:validationHarvestingFS --harvesting AtRunEnd --conditions auto:mc --filein file:TTbar_Tauola_7TeV_cfi_py_GEN_FASTSIM_HLT_VALIDATION.root --mc

Comparison macro for individual steps (efficiency versus eta): AG's private macro (adapted from the official Tracking POG validation)

-- AndreaGiammanco - 08-Mar-2012

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Topic revision: r1 - 2012-03-08 - AndreaGiammanco
 
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