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Monte Carlo quarkonium simulations at A TLAS Darren Price , LANCASTER UNIVERSITY PowerPoint Presentation
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Monte Carlo quarkonium simulations at A TLAS Darren Price , LANCASTER UNIVERSITY International Workshop on Heavy Quarkonium 2007. Based on hep-ph/0003142. Monte Carlo onia samples at ATLAS.

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Monte Carlo quarkonium simulations at ATLAS


International Workshop on Heavy Quarkonium 2007


Based on hep-ph/0003142

Monte Carlo onia samples at ATLAS

  • Official high statistics production samples at ATLAS currently use NRQCD octet processes only. Originally written by S. Wolf, now incorporated into Pythia.
  • Colour octet NRQCD matrix elements describe non-perturbative onia evolution
    • Matrix elements set to values derived from Tevatron data
  • Much interest at ATLAS in producing samples of 2S and 3S states.
    • In Pythia, requires separate production runs so this has not been done yet
    • Currently ME’s for these higher states have not been added into ATLAS Pythia tuning but should be possible based on hep-ph/0003142
  • Are updated ME values available?

Extending processes available in Pythia

  • Only LO order NRQCD processes are implemented in Pythia (as of 6.413)
  • Desirable to extend range of processes we are able to study at ATLAS
    • Pythia can handle showering/hadronisation if provided with short distance cross-section
    • NNLO calculations should be added, MadOnia interfaced, kt factorisation approach?
  • Theoretical cross-sections and distributions for various processes need to be run through detector simulation and reconstruction software to see if we can really see what we hope to see!
  • Can investigate feasibility of excluding or proving various production models at the LHC if we have these processes simulated sooner rather than later
    • After discussions with Lansberg, considering associated charm/beauty production
    • Will be able to look for J/y produced with U, but need processes in Pythia!
  • Would like to be able to compare different MC generators, such as Herwig++

Polarisation and octet evolution in Pythia

  • As standard Pythia does not contain information about octet state spin-alignment so this cannot be determined in the final analysis
    • Would be useful to be able to include and keep track of this polarisation information throughout the evolution
    • Would allow us to run normal simulations through the detector and see effect of detector acceptance with pT, h etc.
    • Reducing dependence on MC templates important, can reduce any unknown systematics and correlations that may be otherwise present
  • Octet states in Pythia currently very simplistic -- states have correct quantum numbers but are assumed to all evolve as either: J/y(8)->g+J/y(1) or U(8)->g+U(1)with the emitted gluon taking away colour having 4 MeV phase space!
  • By changing the mass of the octet quarkonia, can give this gluon a better chance of doing something (anything!) Would like to know if there are any predictions for what values would be sensible, or upper limits?
  • This effects how likely we are to see associated hadronic activity
    • If gluon has ~O(MeV) phase space, have no chance of differentiating octet/singlet evolution based on associated hadronic activity near onia direction after reconstruction