Event Generator Event Generators Information needed Event Generator Information Event Kinematic Information Generated Event Structure – generated particles Particle Decay Particle Interaction - secondaries

Current Generators FORTRAN PYTHIA (an old version current 6.203) HERWIG investigations QQ for B-decays ARIADNE un-investigated (PDFLIB – for parton densities) OO Generators PYTHIA vsn 7 – β release HERWIG under development QQ ?? – Particle Property services Event Generator Maintenance LHCb maintenance – allows rapid response to physics, manpower overhead Central maintenance – converse of the above!

Event Generator Information -track the version and the event generator used -important to keep tab of version – authors change things! -e.g. change in min. bias charged multiplicity between version of PYTHIA -keep track of “private” LHCb changes to a generator -implementation version in LHCb OO code – keep track of the bugs we introduce! (“most reported bugs are due to the experiments interface code” – Sjöstrand)

Event Kinematic Information pp collisons different kinematics for every event x-Bjorken, Mandelstam variables QCD production mechanisms Event type study of b-production/fragmentation mechanisms generator biases at 4-vector level before full detector simulation

Event Particle Listings  Primary particle generation  B oscillations? for detector simulation trigger studies detector studies & corrections All information discussed so far can be generated independently of detector simulation  Standalone program from GEANT simulation ? Advantage: less emphasis on MC production co-ordinator getting things right Disadvantage:maintenance overhead

Particle (B-)Decay Integral part of detector simulation (particular B-decays) Need history information – where did particle come from? mother particle, decay vertices, … forced decay – well-defined code flag for decay modes version of decay package (cf event generator info.)

Particle Interactions GEANT produced secondaries history information: mother particles interaction vertex hadronic/em shower development GEANT mechanism Deal with multiple scatterings/event trigger (event overlay)