Notes on Tau Monte Carlo


Tauola is a tau decay library. It handles polarized tau leptons and should be used rather than working with Pythia directly for taus. I will add notes here on how to use it as I figure things out.

Tauola code is in "tauola_i/" in the CDF code base. Version 2.6 is currently in use.

generatorMods/TauolaModule.hh is the header file. Talk-to parameters are:

Here is how this should work. For more details on running Monte Carlo in general, see this webpage .

path enable AllPath
creator set NSIM

module disable Isajet herwig Bgenerator WGRAD FAKE_EVENT mbr

module enable Pythia
talk Pythia
# Produce t tbar
    msel set 6

module enable TauolaModule
talk TauolaModule
# Inclusive decay mode
  decay_mode_tau+ set 0
  decay_mode_tau- set 0

talk DHOutput
  output setstream * list
  output create main_stream $env(MCGEN_OUTPUT)
  output path main_stream AllPath
  output keepList main_stream \
      LRIH_StorableBank EVCL_StorableBank HEPG_StorableBank

begin -nev $env(NUM_EVENTS)
show timer


This should work with Pythia, Isajet, and Herwig, with the appropriate changes, but I have only tested Pythia.. Note this assumes environment variables NUM_EVENTS and MCGEN_OUTPUT consisting of number of events to simulate, and the name of the output file, respectively, are exported.

Controlling decay modes

Let's say we want to simulate ttbar, with only leptonic decays (say we're looking for a tau and an e or mu). Then in Pythia you can turn off other decay modes of the W through the talk-to, like this:

module enable Pythia
talk Pythia
# Produce t tbar
    msel set 6
      # Force leptonic W decays (decay channels 206, 207, 208 will be used)
      set_mdme -channelIndex=190 -decayType=0
      set_mdme -channelIndex=191 -decayType=0
      set_mdme -channelIndex=192 -decayType=0
      set_mdme -channelIndex=194 -decayType=0
      set_mdme -channelIndex=195 -decayType=0
      set_mdme -channelIndex=196 -decayType=0
      set_mdme -channelIndex=198 -decayType=0
      set_mdme -channelIndex=199 -decayType=0
      set_mdme -channelIndex=200 -decayType=0

The decayType parameter is -1 for channels that are ignored, 1 for channels that are used, and 0 for channels that are counted toward the total width but have decay turned off. Hence we get the right lifetime if we turn off all of these channels by setting them to "0", leaving channels 206, 207, and 208 (i.e. W->l nu for l=electron, muon, tau). For a complete list of decay channels, see


Tauola home page with links to documentation

Tauola status report by T. Moulik

Pasha's tau page, including further links.

Created by Matt Reece ( Jan 31, 2002