• PYTHIA performs the decay of hadrons, if the ctau is within the kinematic range of the CMS detector (used in several official simulations scenarios); a note, the pythiaUESettings, already has a decay of unstable particle included, if ctau<10mm. (= 'MSTJ(22)=2 ! Decay those unstable particles', 'PARJ(71)=10 . ! for which ctau 10 mm', =)

import FWCore.ParameterSet.Config as cms
from Configuration.Generator.PythiaUESettings_cfi import *
generator = cms.EDFilter("Pythia6GeneratorFilter",
                         pythiaPylistVerbosity = cms.untracked.int32(1),
                         pythiaHepMCVerbosity = cms.untracked.bool(True),
                         comEnergy = cms.double(4000.0),
                         filterEfficiency = cms.untracked.double(1),
                         crossSection = cms.untracked.double(-1),
                         maxEventsToPrint = cms.untracked.int32(0),
                         PythiaParameters = cms.PSet(
        pythiaUESettingsBlock,
        processParameters = cms.vstring('MSEL=0           ! User defined processes', 
                                        'MSUB(11)=1       ! fifj->fkfl', 
                                        'MSUB(12)=1       ! fifjbar->fkfkbar', 
                                        'MSUB(13)=1       ! fifibar->gg', 
                                        'MSUB(15)=1       ! fifibar->gZ0', 
                                        'MSUB(16)=1       ! fifibar->gW+', 
                                        'MSUB(28)=1       ! fig->fig', 
                                        'MSUB(30)=1       ! fig->fiZ', 
                                        'MSUB(31)=1       ! fig->fiW', 
                                        'MSUB(53)=1       ! gg->fkfkbar', 
                                        'MSUB(68)=1       ! gg->gg', 
                                        'CKIN(3)=10.      ! minimum pt hat for hard interactions',
                                        'CKIN(4)=100.     ! maximum pt hat for hard interactions'
                                    *   ,'MSTJ(22)=4       ! Decay unstable particles in a cylinder', 
                                    *   'PARJ(73)=2000.   ! max. radius for MSTJ(22)=4', 
                                    *   'PARJ(74)=4000.   ! max. Z for MSTJ(22)=4', 
                                    *    'MDCY(C130,1)=1   ! decay k0-longs', 
                                    *    'MDCY(C211,1)=1   ! decay pions', 
                                    *    'MDCY(C321,1)=1   ! decay kaons'
                                        ),
        # This is a vector of ParameterSet names to be read, in this order
        parameterSets = cms.vstring('pythiaUESettings',
                                    'processParameters')
        )
                         )

• let GEANT do the decay: comment out the lines marked with =* = in the configuration file above

The way the test was done: generated 4000 events, 2000 for each case, keeping the randomNumbers the same, and looked a the number of SimTracks. The configuration file to recreate these events is this one. The files, with their location are: geantDecay and pythiaDecay.

The results are bellow.

My conclusion GEANT is doing well, the background samples used for the Detector readiness studies do contain all the possible hadrons and their decay products (with the pythia+hydjet xsections); (the difference between the 2 data sets I blame mostly on: more decays turned on in GEANT (ok, all) compared to the 3 I specifically had on, and the cut, in the 4000 x 2000 strict cut imposed in the case of the pythia decays ) -- CameliaMironov - 18-Dec-2009