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EvtGen in ATHENA

EvtGen in ATHENA. EvtGen Source code: copy of Babar code + LHCb Pythia6 instead of Jetset + incoherent oscillations + CDF Bs & B-baryons (this is already inside BaBar version) Grid production: a source EvtGen code from

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EvtGen in ATHENA

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  1. EvtGen in ATHENA • EvtGen Source code: • copy of Babar code + LHCb Pythia6 instead of Jetset + incoherent oscillations + CDF Bs & B-baryons (this is already inside BaBar version) • Grid production: a source EvtGen code from atlas/offline/external/EvtGen/source code …libEvtGen.a was distributed in grid production sites. • Users applications were implemented in ATLAS source code, never went beyond ATLAS. • ATHENA interface to EvtGen: • Generators/EvtGen_i/…/EvtDecay • EvtGen is combined with ATHENA Generator that delivers event to HepMC: Pythia, HERWIG, SingleParticleGun. M.Smizanska, LCG Generators meeting, CERN

  2. EvtGen in combination with Pythia, Herwig, HepMC • Spin before EvtGen: • Pythia, Herwig production models no spin degrees. • EvtGen assignes spin, polarization aposteriori – no relation to previous history of the event, no correlation between different objects in the same event. • Where to decay Excited states: • Ideally strong and elmg decays should be done in EvtGen – spin considerations • Problem: Pythia (Herwig) hadronization models correlated with decays of excited states and tuned to get correct b-jet multiplicities. If strong, elmg decays moved to EvtGen – need to check tuning againg. • Interference effects: • EvtGen technically allows interference effects. Strictly speaking should allow also interference between resonant – non-resonant final states or between different resonances. • In Bs we added also interference between DB=2 (mixing) and DB=1 decay amplitudes needed scope with CP violation. • Store polarization information in HepMC? • HepMC allows store complex spinor with each particle. We have never used this, no sence for geant, that is spin-blind. We have no applications require this. M.Smizanska, LCG Generators meeting, CERN

  3. Conclusions • ATLAS production use EvtGen for selected exclusive weak decays. • Never used for inclusive production. • Soon ATLAS is going to have a person with 30% just on EvtGen. • We will improve collaboration with LCG, but must solve many technical problems, in particular differences between LHCb and ATLAS EvtGen interfaces. • Common LHC tunings should be done. • Clarify about spins in HEPMC, but currently no requests for this. What about LHCb? M.Smizanska, LCG Generators meeting, CERN

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