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NLO Vector+Jets Predictions with B lack H at & SHERPA

NLO Vector+Jets Predictions with B lack H at & SHERPA. David A. Kosower Institut de Physique Th é orique , CEA– Saclay on behalf of the BlackHat Collaboration Z. Bern, L. Dixon, Fernando Febres Cordero , Stefan Höche , Harald Ita , DAK, Daniel Maître , Kemal Ozeren

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NLO Vector+Jets Predictions with B lack H at & SHERPA

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  1. NLO Vector+Jets Predictions with BlackHat& SHERPA David A. KosowerInstitut de Physique Théorique, CEA–Saclay on behalf of the BlackHat Collaboration Z. Bern, L. Dixon, Fernando Febres Cordero, Stefan Höche, HaraldIta, DAK, Daniel Maître, Kemal Ozeren [1009.2338, 1108.2229, & work in progress] ICHEP 2012, MelbourneJuly 5, 2012

  2. Vector+Jets • Background to • Many searches of new physics • Measurements of Higgs properties • Measurements of top properties • Standard candle for checking our understanding of Standard-Model processes

  3. Next-to-Leading Order in QCD • Precision QCD requires at least NLO • QCD at LO is not quantitative: large dependence on unphysical renormalization and factorization scales • NLO: reduced dependence, first quantitative prediction • NLO importance grows with increasing number of jets • Applications to Multi-Jet Processes: • Measurements of Standard-Model distributions & cross sections • Estimating backgrounds in Searches  L. Dixon’s talk • Expect predictions reliable to 10–15% • <5% predictions will require NNLO

  4. The On-Shell Revolution • Ingredients to NLO calculations • Tree-level 2  V+n and 2 V+n+1… now with improved efficiency (Britto, Cachazo, Feng, Witten; Dixon, Henn, Plefka, Schuster) • NLO parton distributions • General framework for numerical programs (Catani & Seymour) • One-loop 2  V+n The on-shell revolution has broken the bottleneck: n=3,4,5 BlackHat Implementation • Numerical implementation of on-shell methods for one-loop amplitudes • Automated implementation  industrialization • Do algebra numerically, analysis symbolically (“analytically”) • SHERPA for real subtraction, real emission, phase-space integration • Distribute results via ROOT n-tuples

  5. Lots of revolutionaries roaming the world • BlackHat • CutTools+HELAC-NLO: Ossola, Papadopoulos, Pittau, Actis, Bevilacqua, Czakon, Draggiotis, Garzelli, van Hameren, Mastrolia, Worek & their clients • Rocket: Ellis, Giele, Kunszt, Lazopoulos, Melnikov, Zanderighi • Samurai: Mastrolia, Ossola, Reiter, & Tramontano • NGluon: Badger, Biedermann, & Uwer • MadLoop: Hirschi, Frederix, Frixione, Garzelli, Maltoni, & Pittau • Giele, Kunszt, Stavenga, Winter • Ongoing analytic work • Almeida, Britto, Feng & Mirabella

  6. W+4 Jets • Scale variation reduced substantially at NLO • Successive jet distributions fall more steeply • Shapes of 4th jet distribution unchanged at NLO — but first three are slightly steeper

  7. CMS measurements [1110.3226] — but no comparison to NLO yet

  8. Comparisons to Atlas data 36 pb−1 [1201.1276]

  9. Z+4 Jets

  10. Comparison to Data ATLAS 36 pb−1 [arXiv:1111.2690] Cross sections for Z/γ*+≥1,2,3,4 jets, anti-kT, R = 0.4 Small scale variation, good agreement with data Much more to come!

  11. W+5 Jets • Scale dependence narrows substantially at NLO

  12. Jet Ratios • Relaxation of kinematic restrictions leads to NLO corrections at large pT in V+3/V+2, otherwise stable • Ratio is not constant as a function of pT — fits to α+βn will haveα & β dependent on pTmin

  13. Summary • On-shell methods have matured into the method of choice for NLO QCD calculations for colliders • Calculations with high multiplicity are mature for experimental comparisons • Probe wide variety of kinematic regimes, establish confidence for extrapolations into search regions

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