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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
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


Evtgen in combination with pythia herwig hepmc
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


Conclusions
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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