1. NLO Vector+Jets Predictions with B LACK H AT & SHERPA David A. Kosower Institut de Physique Théorique, CEA–Saclay on behalf of the B LACK H AT Collaboration Z. Bern, L. Dixon, Fernando Febres Cordero, Stefan Höche, Harald Ita, DAK, Daniel Maître, Kemal Ozeren [1009.2338, 1108.2229, & work in progress] ICHEP 2012, Melbourne July 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 B LACK H AT 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 – B LACK H AT – 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 4 th 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-k T, 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 p T — fits to α+β n will have α & β dependent on p Tmin

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