Kalanand's July 2013 Log

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July 11th

FastSimulation/InSituPileUpProducer to add pile up efficiently

From Sridhara Dasu. Try out this module to produce your own events with large pile up, generated in-situ using Pythia8, using CMSSW FastSimulation program. There is no need for large pile up minbias samples ... I suggest using Pythia8 for hard event also, but you should be able to use any generator.

Instructions for checkout build and run a test:
  scram project CMSSW CMSSW_5_3_10_patch2
  cd CMSSW_5_3_10_patch2/src/
  mkdir FastSimulation
  cd FastSimulation/
  cvs co -d  InSituPileUpProducer UserCode/dasu/InSituPileUpProducer
  cd InSituPileUpProducer/
  scram b
  cd test
  cmsRun InSituPileUpProducer_cfg.py >& PU140.log&
The test produced 100 Z->mu+mu- events with average PU = 140 at 5 Hz on an AMD Opteron(tm) Processor 6176 (just an ordinary box Good thing is that you get AODSIM ... the objects that you really want for running existing analyses. Of course, people need the upgrade geometries in FastSimulation for this to be truly useful for long term. It will work nicely for 2015-2017 studies with "existing" detector.

July 17th

Pdf Uncertainty Estimation: recipe from Juan Alcaraz

a) The PDF4LHC prescription is explained at arXiv:1101.0538 (look at the NLO part and ignore the αS additional discussions, which is peanuts compared to the bulk of the error). I would use at present CT10, MSTW08 and NNPDF21. You can even use the NNLO versions of them if you like (but I do not expect that this will decrease your uncertainties).

b) Some code for reweighiting on AODSIM formats can be found in the CMSSW package
But you'll likely need to install the LHAPDF libraries locally (and do not run this over GRID: you may fail dramatically). Look also at:


for instructions and warnings. It may even be outdated for the newset versions, I do not know.

c) Finally, I even recommend to go outside CMSSW if you have all the PDFInfo information in ntuples. I am attaching a piece of code that shows how to reweight in a simple way each PDF member. You always need to install locally the LHAPDF libraries in any case.

Attached file:LHAPDF_reweighting.C

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Last modified: Thu June 18 10:07:35 CST 2013