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POWHEG Adaptation of the Baur Zγ Generator

POWHEG Adaptation of the Baur Zγ Generator. Lindsey Gray University of Wisconsin at Madison Weekly Meeting 10 June, 2009. Action Items. Show plots of pythia based CMSSW analysis, scaled by appropriate factors. First results of multivariate analysis

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POWHEG Adaptation of the Baur Zγ Generator

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  1. POWHEG Adaptation of the Baur Zγ Generator Lindsey Gray University of Wisconsin at Madison Weekly Meeting 10 June, 2009

  2. Action Items • Show plots of pythia based CMSSW analysis, scaled by appropriate factors. • First results of multivariate analysis • Resurrect and show plots from RCT Calibration Routines • Status of POWHEG adaptation of Baur’s MC Generator • Draft for Multi-boson group talk in 1 week • Kolmogorov test between POWHEG and Baur plots • Comparing POWHEG LO to Tevatron result Lindsey Gray, UW Madison

  3. Draft of Multi-boson talk 1 week from now

  4. Outline • Overview of POWHEG • Motivation & Definition • Current Results of Adapting Baur’s MC • Development Strategy & Status • Born Level Results & Comparison to Baur’s MC • Including Anomalous Couplings • Preliminary Leading Log Results • Conclusions & Next Steps Lindsey Gray, UW Madison

  5. Current Status of Development • All necessary portions of Baur’s NLO calculation have been extracted in POWHEG framework • Charged leptons only for now • Testing is in progress: • Born matrix element result is fully tested • 2.5% normalization difference relative to Baur LO • Shapes match • Results to be shown • Collinear & Virtual corrections implemented • Numerically stable Leading Log result • Plots to be Shown • Real matrix element result is implemented • Currently debugging & testing Lindsey Gray, UW Madison

  6. Shape Comparison: Diboson Mass & Lepton PT • All plots are area normalized. • 2.5% normalization difference • Known effect since Baur’s code uses narrow width approx. and POWHEG code has finite Z width. • Using narrow width approx. in POWHEG code makes 2.5% normalization difference < 1% • All Born level shapes agree! • Kolmogorov test yielded > .99 match probability for each differential cross section Baur POWHEG Lindsey Gray, UW Madison

  7. Shape Comparison:Photon PT, Lepton η & Photon η Baur POWHEG Lindsey Gray, UW Madison

  8. Shape Comparison:Photon PT + Anomalous Coupling • ACs are automatically included in the routines from Baur’s code. • Scaling is the same between Baur MC and POWHEG. Lindsey Gray, UW Madison

  9. Preliminary Leading Log Results • Includes virtual and collinear contributions to the cross section • Large cancellations between born, virtual, collinear terms • 2.27pb for SM Zγ • ~.5% uncertainty in cross section with 250k events • Close to ~.2% expected error • Resulting distributions look OK Lindsey Gray, UW Madison

  10. Preliminary Leading Log Results Lindsey Gray, UW Madison

  11. Conclusions and Next Steps • Determine source of normalization difference at leading order. • All of the necessary components for NLO Zγ cross section calculation are in place in POWHEG • What remains now is extensive testing, debugging and comparison to Baur’s NLO code • Once NLO calculation is fully ported and tested • Test event generation • Compare unweighted event kinematics distributions to NLO differential cross sections • Run trials interfacing POWHEG lhe-event file to Pythia, Herwig, et al. and cross check results. Lindsey Gray, UW Madison

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