3.2 From Monte Carlo Input to Datasets

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Goals of this page:

This page is intended to familiarize you with the generation of the simulated event data. In particular, you will learn:

  • how this data is used in CMS studies
  • the procedure to define events samples to be generated
  • what to do if your favourite physics channel is not among the available event sample.



The simulated Monte Carlo (MC) event samples are on one hand used to represent the real data before the experiment starts and on the other hand will be used to compare with the real collision data when the experiment has started data taking.

Production Steps

The event samples to be produced are discussed and defined in the Physics Analysis Groups. The groups make a production request to the Production team which then launches the production using the grid resources.

The starting point of a MC dataset is a process description for a generator like Pythia, Herwig or Alpgen where the specific physics channel to be produced is described. The production usually takes place in steps:

  • event generation (GEN) - generation of the particle collision process and of the resulting secondary particles
  • simulation (SIM) - propagation of the particles through the CMS detector and simulation of their interactions with the detecor material
  • digitization (DIGI) - transformation of the simulation output (energy deposits in the detector material) to detector signal equivalent to the real data
  • reconstruction (RECO) - reconstruction of the particles and physics objects from the detector signals (this step is the same for simulated and real data and the resulting dataset is formally equivalent to the real data).
The details of these steps are described in Chapters 6(7?) to 8(9?), see in particular the introductory sections WorkBookGenIntro, WorkBookIntroReco and WorkBookIntroHiLevelReco. The details of the data formats produced by these steps are given in section WorkBookDataFormats. In most cases the analysis is done on the data which has gone through all the steps above.


The available samples are listed in the DBS/DLS browser use of which is described in section WorkBookDataSamples. If the channel of your interest has not been produced, you should discuss it with the respective physics group convener to decide whether a production request can be made.

Information Sources

Review status

Reviewer/Editor and Date (copy from screen) Comments
CMSUserSupport - 11 Sep 2007 created the page and the basic contents

Responsible: ResponsibleIndividual
Last reviewed by: YourName - 06 Dec 2006

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Topic revision: r6 - 2007-09-28 - KatiLassilaPerini



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