H   Final State 3rd LHC Higgs Cross section Workshop Bari, Nov. 4-5 2010

1. H Final State 3rd LHC Higgs Cross section Workshop Bari, Nov. 4-5 2010 Susan GASCON-SHOTKIN (IPN Lyon/UCB Lyon 1), Marumi KADO (LAL) Planned activities and topics to be studied, status List of LO/NLO Monte Carlos used Wish List for theorists Status of the common selection cuts among ATLAS and CMS

2. Planned activities and topics to be studied • Differential K-factors : Detailed studies in progress for both signal and gg backgrounds. The principal topic as regards the Higgs signal. • Compute the interference between signal and background : Existing work by L. Dixon et al on destructive resonance-continuum interference (hep-ph/0302233) • Background determination methods (data-driven, non-data-driven): • Non-data-driven: Reweight LO(+)/NLO hadronised backgrounds with NLO/NNLO • partonic-level generators using differential k-factors (above). • Data-driven: Measure background from sidebands. Measurements to be validated by • direct photon cross-section measurements. Definition of sidebands: A potential topic • for an ATLAS-CMS agreement • Pseudo-isolation : A criterion which affects background measurements : A potential topic for an • ATLAS-CMS agreement • Joint discussion on systematic error calculations, for signal (differential k-factors) and • Background (sideband definition) • Determine theoretical precisions that we need to have in the control regions and in the signal region

3. List of LO/NLO Monte Carlos used so far or shortly to be used LO (+) : Signal and Background: PYTHIA (Sjostrand et al), MadGraph (Stelzer, Maltoni et al) [no box diag.], ALPGEN (Mangano et al), [ “ ] SHERPA (Gleisberg, Hoche, Krauss et al.) [“ ] >LO: NLO: Signal: Generators: MC@NLO (Frixione, Webber et al) [gluon fusion only], POWHEG (Nason et al) Backgrounds: gg + X: Calulators: DIPHOX (Binoth, Guillet, Pilon et al ) (Fixed-Order) gamma2MC (Bern, Dixon, Schmidt) (Fixed-Order) ResBos (Balazs, Nadolsky, Yuan) (Resummation) g + X: Calculators: JETPHOX (Aurenche, Fontannaz,Guillet et al) (Fixed-Order) NNLO: Signal: Calculators: HNNLO (Catani, Grazzini) [gluon fusion only] FEHIP (Anastasiou, Melnikov, Petriello) [gluon fusion only] Backgrounds: gamma2MC(Bern,Dixon,Schmidt) [gg box] ResBos (Balazs, Nadolsky, Yuan) [gg box]

4. Generators/calculators of SM +X processes BOX BORN ONE FRAG TWO FRAG DIRECT FRAGMENTATION Currently DIPHOX contains the most complete treatment of fragmentation

5. Generators/calculators of SM +X processes gamma2MC, NLO Bern, Dixon, Schmidt, hep-ph/0211216, 2002 RESBOS Balazs, Berger, Mrenna, Yuan, hep-ph/9712471, 1997 DIPHOX Binoth, Guillet, Pilon, Werlen, hep-ph/9911340, 2000 FIXED ORDER : NLO NLO with NNLL Resummation FIXED ORDER : NLO BORN + FRAG (and NLO corrections)‏ BOX (and NLO corrections)‏ Resbos only 1-frag : - LO, effectively in Resbos - NLO in Diphox 2-frag : DIPHOX only (NLO)‏

6. SHERPA Version 1.2.2 now includes matching between Matrix Element and Parton shower photons, to be validated by direct photon measurements (Gleisberg, Hoche, Krauss, Schonherr, Schumann, Siegert , Winter, JHEP 02 (2009) 007 , Phys.Rev.D81:034026,2010) Diphoton production at Tevatron Recently published by D Phys.Lett.B690:108-117,2010 Isolated hard photons with: E1> 21 GeV E2> 20 GeV |eta |< 0.9 Isolation: Et(R = 0.4) –E < 2.5 GeV Here: Azimuthal angle between the diphoton pair ME/PS simulation using Sherpa 1.2.2 with QCD+QED interleaved shower and merging

7. Pseudo-isolation What are the particle- and partonic-level isolations corresponding to reconstructed-level isolation? Stability of k-factors as a function of pseudo-isolation Compatibility of theoretical pseudo-isolation and experimental isolation constraints from a theoretical point of view. New DIPHOX version has discretized version of isolation cone proposed by S. Frixione to avoid problem of Large Logs when Rexp 0 and ET max  0

8. Diphoton cross-sections at different luminosities Diphox [J.P. Guillet, E. Pilon, T. Binoth] Gamma2MC [Z. Bern, L. Dixon, and C. Schmidt] - For all the cross sections, pt_gamma > 5 GeV is required - Born, one frag and two frag contributions at LO and NLO are calculated with DIPHOX - Box contributions are calculated with GAMMA2MC at LO and NLO, except at Ecom = 900 GeV, where it is calculated with Diphox (only at LO, because Diphox does not compute Box contribution at NLO

9. Doubly-differential Reweighting of gg + x and gg  H gg Inspired by Dissertori et al, JHEP0607:037,2006. Done for Hgg signal and gg SM backgrounds (for the first time) in CMS: See mini-talk by N. Chanon qT Mgg qT Reweighting of MC@NLO gg H γγ with K(qT ,Ygg) to HNNLO Simultaneous reweighting of Madgraph Born and PYTHIA Box gg H γγ with K(qT , Mgg) to DIPHOX and gamma2MC

10. Signal-Background interference L. Dixon and S. Siu, hep-ph/0302233 Destructive interference between resonance ggHgg and continuum gggg processes Effect estimated to be ~5% over the pertinent mH range

11. Wish List for theorists • 1.- A robust procedure for the estimation of systematic errors on differential • cross-section predictions (in particular on qT) • 2.- A procedure for the estimation of error on fragmentation • 3.- Is an NLO version of SHERPA on the horizon? Can we use SHERPA as it is • with a simple k-factor? • 4.- Definition of parton-level pseudo-isolation cuts and the best scales to use

12. Status of the common selection cuts between ATLAS and CMS For the moment we have established common base acceptance cuts without isolation: |hg| <2.5 Etg > 20 GeV We may add isolation later. Less relevant for signal than for background

13. Acknowledgements N. Chanon, Z. Bern, L. Dixon, C. Schmidt, J-Ph. Guillet, E. Pilon, M. Grazzini, F. Krauss, F. Siegert, G. Dissertori, F. Stoeckli, C. Mariotti, A. Korytov, V. Sharma, M. Gataullin, M. Pieri, J. Branson, S. Ganjour The organizers (N. DeFillippis, C. Mariotti and local organisers) and convenors (C. Mariotti, R. Tanaka, S. Dittmaier, G. Passarino, M. Felcini, J. Yu)