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MATCHING NLO QCD CALCULATIONS AND PARTON SHOWERS – A POSSIBLE UPDATE

MATCHING NLO QCD CALCULATIONS AND PARTON SHOWERS – A POSSIBLE UPDATE. Thomas Sch örner-Sadenius Hamburg University HERA-LHC Workshop 26/27 M arch 2004. ACHIEVEMENTS NLO weights + PS. Rearrange NLO calculation in PS region such that negative weights are avoided

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MATCHING NLO QCD CALCULATIONS AND PARTON SHOWERS – A POSSIBLE UPDATE

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  1. MATCHING NLO QCD CALCULATIONSAND PARTON SHOWERS – A POSSIBLE UPDATE Thomas Schörner-Sadenius Hamburg University HERA-LHC Workshop 26/27 March 2004

  2. ACHIEVEMENTSNLO weights + PS • Rearrange NLO calculation inPS region such that • negative weights are avoided • the total weight is given by the real correction to the Born level • For this purpose a cut-off  that isolates the analytic/singular partof the cross-section. • (B. Pötter, Phys. Rev. D 63 (2001) 114017) TSS: NLO+PS

  3. GRAPHICALLYNLO weights + PS • Implementation in DISENT • Split PS and hard region with technical parameter Rtech ~ 1 • in hard region use BGF/QCDC matrix elements • in PS region use QPM configuration with NLO weight (last page) • avoid double-counting • (B. Pötter, T. Schörner, Phys. Lett. B 517 (2001) 86:“… the QCD-improved parton model …” ) TSS: NLO+PS

  4. RESULTSusing ZEUS inclusive jet data in lab Can describe at the same time inclusive cross-sections (normalization)and jet shapes (soft region). TSS: NLO+PS

  5. IDEAextend to jets in Breit (‘one order higher’) • Derive smin function for the dijet/Breit case (many parts can be taken from PSS program JetViP). DONE • Implement in DISENT. DONE • Test  Problems • many events deliver logs with negative arguments (log(-(u+t)/s) etc.) • Mistake in adapting JetViP parton array convention to DISENT? • Principal problem? TSS: NLO+PS

  6. SO WHAT?have to re-think, re-calculate, • Any help from theorists or experimentalists with better insight into the technicalities highly welcome. • … although probably practical use limited: • only FSPS • theoretical criticisms • … TSS: NLO+PS

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