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Revisiting NLO QCD Calculations and Parton Showers: A Potential Update

Achievements in NLO weights and parton showers are discussed, aiming to rearrange NLO calculations in the PS region to avoid negative weights, focusing on implementing improvements in DISENT software. Results using ZEUS data show potential for describing inclusive jet data and shapes in the soft region. Ideas to extend to Breit jets and challenges in implementation are explored.

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Revisiting NLO QCD Calculations and Parton Showers: A Potential 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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