Results from the LHC Higgs Cross Section WG

1. LHC2TSP Results from the LHC Higgs Cross Section WG Reisaburo TANAKA (LAL-Orsay) On behalf of the LHC Higgs Cross Section Working Group Implications of LHC Results for TeV-Scale Physics Workshop Aug. 29 - Sep. 2, 2011 @ CERN LHC Higgs Cross Section Working Group

2. Contents • LHC Higgs Cross Section Working Group • Higgs Cross Sections and Branching Ratios • NLO Monte Carlo and Higgs pT Distribution • Jet-bin Uncertainty in Exclusive Analysis • Standard Model Backgrounds and Interferences • Heavy Higgs Line Shape • Beyond Standard Model Higgs Summary Disclaimer: • Review by experimental physicist on current issues. • Many thanks to my colleagues in LHC Higgs XS WG for discussions. LHC Higgs Cross Section Working Group

3. 1. LHC Higgs Cross Section Working Group How the LHC Higgs Cross Section WG contributed and what will do for the future ? Higgs boson search in three directions. • Light Higgs MH < 140 GeV H→γγ,bb,ττ,WW,ZZ JPC, Yukawa, H self-coupling • Heavy Higgs MH > 500 GeV H→WW,ZZ JPC, HVV, VLVL scattering • BSM Higgs MSSM, NMSSM, Composite, Higgsless, … ATL-PHYS-PUB-2011-135 CMS-PAS-HIG-11-022 LHC Higgs Cross Section Working Group

4. SM XS TF MC Group Statistics Forum LHC Higgs Cross Section Working Group ATLAS ⊕ CMS ⊕LHCb⊗ Theory Creation announced in January 2010. Kickoff meeting on February 3, 2010. Workshops in Torino (Nov. 2009), Freiburg (April 2010), CERN (July 2010), Bari (Nov. 2010), BNL (May 2011), Paris (Nov. 2011) Task: SM and MSSM Higgs Cross Section and BRs • Compute and agree on cross sections and BRs • Use the same Standard Model input parameters • Uncertainty estimation (scale, αs, PDF, etc.) • Monte Carlo at NLO for signal and bkg. • Define pseudo-observables • Cross sections of background SM processes 16 Working Subgroups: ggF, VBF, WH/ZH, ttH, MSSM H→γγ/WW/ZZ/ττ/bb, H± PDF, BR, NLO MC, Pseudo-Observables LHC Higgs Combination WG PDF4LHC WG

5. LHC Higgs XS WG CERN Report • Contents: (work in progress) • Results on Higgs production ggF, VBF, WH/ZH, ttH • Results on Higgs decay H→γγ/WW/ZZ/ττ/bb • Recipe to assess THU+PU for distributions • Distributions with THU+PU  • BRs: THU+PU  • MSSM: general recipes and specific scenario(s) • PseudoObs: heavy Higgs MH/ΓH, signal-bkginterf.  • NLOMC: tools and error estimates for acceptance  • Specific topics: jet veto, Higgs pT, etc. CERN Report went out before the 1st Higgs results of LHC ! 64 authors 151 pages 370 references LHC Higgs Cross Section Working Group

6. Higgs Cross Section Issues ggF, VBF, WH/ZH, ttH, BSM Higgs Jet bin uncertainty H+0,1,2-jets Higgs Cross Sections (inclusive/exclusive) Differential K-factors (effect of jet-veto etc.) QCD correction NkLO + NmLL EW correction, Mixed QCD-EW Heavy Higgs Line Shape SM Backgrounds & Interferences gluon W/Z top/bottom Higgs decay Branching ratios (QCD/EW corr.) Higgs new quarks W/Z Higgs pT (soft gluon resummation) PDF+αs uncertainties Renormalization/Factorization scale dependence LHC Higgs Cross Section Working Group

7. Tools for Higgs Physics ggF, VBF, WH/ZH, ttH, MSSM Higgs Cross Section ggF HIGLU(NNLO QCD+NLO EW) iHixs(NNLO QCD+NLO EW) FeHiPro(NNLO QCD+NLO EW) HNNLO(NNLO QCD) ggh@NNLO(NNLO QCD) VBF VV2H (NLO QCD) VBFNLO(NLO QCD) HAWK (NLO QCD+EW) VBF@NNLO (NNLO) WH/ZH V2HV (NLO QCD) VH@NNLO (NNLO) ttH HQQ(LO QCD) bbH bbH@NNLO(NNLO QCD) + private codes. Higgs Decay HDECAY (NLO) Prophecy4f(NLO) FeynHiggs, CPSuperH gluon W/Z top/bottom Higgs W/Z Higgs pT HqT(NLO+NNLL) ResBos(NLO+NNLL) NLO MC aMC@NLO, POWHEG, SHERPA, HERWIG++ MCFM PDF: MSTW2008, CT10, NNPDF2.1, etc. LHC Higgs Cross Section Working Group

8. 2. Higgs Cross Sections and Branching Ratios • NNLO(+NNLL) QCD calculations for ggF, VBF, WH/ZH and NLO for ttH. • NLO electroweak radiative corrections (O~5-10%) assume factorization QCD vs EW corr. • PDF uncertainty defined with envelope of MSTW, CTEQ and NNPDF (PDF4LHC recipe). K-factor, QCD scale and PDF uncertainties at 7TeV Note: Scale and PDF+αs uncertainties are handled separately according to LHC Higgs combination WG’ prescription. (ATL-PHYS-PUB-2011-011,CMS NOTE-2011/005) LHC Higgs Cross Section Working Group

9. Higgs Decay Branching Ratios What are the theory (THU) + parametric (PU) uncertainties for branching ratios ? Use HDECAY and Prophecy4f for best estimate. Small uncertainties relative to scale and PDF uncertainties in Higgs production. Relatively large uncertainties for H→γγ, ττ at low MH. A. Denner et al., arXiv:1107.5909 LHC Higgs Cross Section Working Group

10. 3. NLO Monte Carlo and Higgs pT Distribution • NLO MCs became the de facto for physics analysis at LHC ! • Exist for ALL Higgs (but gg→ϕ, bbϕ) signals and major SM backgrounds. • Critical for exclusive H+1-jet analysis. • NLO MC for H+2(3)-jet for VBF channel also exist, including qqV, qqVV. 2011.8 • * Zbb work in progress. VBF dedicated MC: HAWK, VBFNLO LHC Higgs Cross Section Working Group

11. Higgs pTSpectrum • Higgs pT can be discriminant variable against bkg. • MC event reweighting via Higgs (pT,Y). • Due to its intrinsic harder Higgs pT spectrum, POWHEG gives ~15% lower efficiency than HqT in H→WW. (POWHEG MC is reweighted to HqT of NLO+NNLL). No reweighting for MC@NLO. • Can we learn from Z(W), ttbarpT spectrum ? NNLO NLO CERN Report 2011-002 LHC Higgs Cross Section Working Group

12. 4. Jet-bin Uncertainty in Exclusive Analysis • Exclusive analysis improves S/N, ex. H→WW→lνlνvsttbar background. • What are the uncertainties for the H+0,1,2-jet bins ? • Should they be taken from fixed-order NNLO, or from elsewhere ? • Given a set of uncertainties how do we treat correlations between the jet-bins ? • Fixed-order expansion shows evidence of large logarithms. The reduction in scale variation for small pT is artificial because of cancellations between large K-factors and large logarithms. C. Anastasiou et al., JHEP 0709 (2007) 018 ATLAS-CONF-2011-134 LHC Higgs Cross Section Working Group

13. Perturbative Uncertainties in Jet-bins • The fixed-order perturbative series for σtotal, σ≥1, σ≥2 can be uncorrelated in perturbative uncertainties: • The covariance matrix for the exclusive jet cross sections: Logarithms of ln(mH/pTcut) appear in σ≥1,2 cross section, but not the total; assume these terms dominate error. Which uncertainty for 2-jet bin with VBF topology ? I. Stewart and F. Tackmann, arXiv:1107.2117 LHC Higgs Cross Section Working Group

14. 5. Standard Model Backgrounds and Interferences Irreducible backgrounds: WW and ZZ in H→WW/ZZ→4f. http://lpc.web.cern.ch/lpc/ LHC Higgs Cross Section Working Group

15. Standard Model Background Estimation Keyword = ‘Data driven background estimation’ • ABCD method • Assume Cut1&2 are not correlated. • Then estimated signal is . • α method • When extrapolation cannot be done with data, use MC, • Backgrounds are estimated in multi-dimensional phase space (WW, top, W/Z+jets rich). Ex. H→WW*→lνlν … Higgs signal … small !! But extrapolation from control to signal region is delicate issue. Not necessarily guaranteed for different phase space. • Shape uncertainty ? • Spin correlation in signal and backgrounds ? • Signal and background interference effect ? • Missing Feynman diagram ? • Uncounted effect ? • … Cut2 MA MB NA NB Cut1 ATLAS-CONF-2011-134 LHC Higgs Cross Section Working Group

16. Effect of Single-Resonant Diagrams • qq/gg→WW/ZZ are important irreducible backgrounds for H→WW/ZZ→4f. • gg/qq 3-5%@7TeV (4% for H+0j, 7% for H+1j) and 10-30%@14TeV. • Non-negligible effects for light Higgs from ‘single-resonant diagrams’. • Large increase in NLO cross section by +55% for qq→ZZ* (MCFM v6.0) ! • Negative interference effect between gg→H→WW→lνlν and gg→WW. • -10% effect for MH<140GeV if MT<MH cut is not applied. • Now NLO MCs (POWHEG, aMC@NLO) handle ‘single-resonant diagrams’. (J.M. Campbell et al.,arXiv:1107.5569). With single-resonant diagram ← Double resonant → Single resonant + many grc(KEK) ZZ Single-W saga for searches at LEP2 Zγ* γ*γ* Double-resonant diagram only pp→4f,6f era for LHC ! LHC Higgs Cross Section Working Group

17. LO/NLO MC for qq/qg/gg→WW/WZ/ZZ 2011.8 Current ‘champs de bataille’ ! • MCFM: v6.1 will contain the gg→WW with a massive top in the loop. • LO ME MC like CompHEP/Grace/MadGraph/Phantom/Sherpa/WHIZARD/etc. are also useful. • gg2WW/ZZ: The gg→H→VV and continuum interference is now in gg2WW and will be in gg2ZZ. • aMC@NLO: Now available for qq→WW/WZ/ZZ at NLO and also gg→WW/ZZ (still private). • POWHEG: WW/WZ/ZZ exist. Does not include gg→VV*, thus one needs to use gg2WW/ZZ or others. • SHERPA: Work in progress for MCFM implementation for full NLO interface. • MCFM, gg2WW/ZZ, aMC@NLO should allow us to study the interference gg→H→VV and SM bkg. • * Tau polarization implementation • is experiment dependent. • ** Needs code hack. • *** Except ZZ. LHC Higgs Cross Section Working Group

18. 6. Heavy Higgs Line Shape • Now LHC searches for heavy Higgs up to 600 GeV. We are studying the heavy Higgs searches in gg→H→WW→lνqq, gg→H→ZZ→llll,llνν,llqq etc. • What is the limitation of narrow Higgs-width approximation to decouple Higgs production and decay, then adopting ad-hoc Breit-Wigner for Higgs decay in MC ? • The effect of interference between Higgs and SM bkg. due to large Higgs width ? • What is the best strategy to go beyond MH=600 GeV ? • Higgs boson tames the bad high-energy behaviour of WW scattering. • Revisit longitudinal VLVL scattering modes ? • 2D scan in (MH, ΓH) for spin-0 particle search ? gluon W/Z top/bottom gg→W+W-→e+νeμ-νμ Higgs Higgs – spin 0 W/Z J.M. Campbell et al.,arXiv:1107.5569 LHC Higgs Cross Section Working Group

19. Heavy Higgs Cross Section and Line Shape Large distortion in Higgs invariant mass spectrum for heavy Higgs. C. Anastasiou et al., arXiv:1107.0683 G. Passarino, talk given at BNL Higgs XS WS • Propagator scheme vsBreit-Wigner • 20-30% difference in normalization and line shape. • Default option in iHixs program • Seymour option in iHixs program • Resummation of VV→VV scattering. • Improved s-ch approximation Seymour scheme tries to simulate the effects of signal-background interference off the resonant peak. Default scheme for purely Higgs signal cross-section. Deviations wrt zero-width approximation are +30% ~ -20% difference in XS for MH<600GeV. MH=600GeV MH=800GeV Seymour Defalut LHC Higgs Cross Section Working Group

20. Fourth Generation Model 7. Beyond Standard Model Higgs Fourth Generation Model • Unitarity argument puts MQ4<500-600GeV. MD4=ML4=600GeV (Down type quark and charged/neutral leptons) MU4- MD4= [ 1 + 1/5*ln(MH/115) ] * 50 GeV for EW precision measurement. Production and Decay • Expect x9 enhancement in EFT with additional quark doublet. • H→γγ - Cancellation in ggF production enhancement (x9) and decay suppression (x1/8). • H→WW/ZZ - Factor 4~9 enhancement over SM. • Recent calculations on NLO EW radiative corrections in the fourth generation mode for Higgs production (arXiv:1108.2025) and decay (Prophecy4fv2) indicate very large corrections. Full listings of numbers and figures at https://twiki.cern.ch/twiki/bin/view/LHCPhysics/SM4At7TeV Top/bottom + heavy quarks Without NLO EW corrections

21. Fermiophobic Higgs Model • Assume Yukawa coupling off and SM like HVV coupling. • For Higgs production cross sections, NNLO VBF, WH/ZH numbers can be used. • EW radiative corrections are unknown in fermiophobic scenario, assign ±5%. HDECAY version 4.00 Excess over SM for MH<120GeV Full listings of numbers and figures at https://twiki.cern.ch/twiki/bin/view/LHCPhysics/Fermiophobic LHC Higgs Cross Section Working Group

22. Summary • LHC Higgs Cross Section WG is open forum for experimentalists and theorists. • ATLAS and CMS are using the common inputs since the very beginning of LHC data ! • LHC Higgs Cross Section WG is working on many issues. • Common Standard Model input parameters. • Higgs XS and BR for Standard Model and BSM Higgs. • PDF, NLO Monte Carlo, Pseudo-Observables. • Recommendations on theory uncertainties. • New issues are rising up. • Interferences between Higgs and SM backgrounds. • Heavy Higgs line shape. • QCD and EW radiative corrections for BSM Higgs physics. • Future • Complete calculations of MSSM Higgs as SM Higgs. • NNNLO calculations, true NNLO Monte Carlo ? • LHC Higgs Cross Section WG is open for everyone. • Subscribe to mailing list lhc-higgs@cern.ch. • All information can be found at our TWiki page, https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections. Luminosity? I speak C++, Python and ROOT, and 7 TeV. I speak Fortran. Started to learn PAW, and 14 TeV. ScuoladiAtene@MuseiVaticani LHC Higgs Cross Section Working Group

23. LHC2TSP Workshop Backup Backup LHC Higgs Cross Section Working Group

24. LHC Higgs Cross Section WG Organization https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections LHC Higgs Cross Section Working Group

25. Interference in H→WW/ZZ→4f Decay • Quite often Higgs production rate is calculated using PDG Br(H→ff) values. • Inaccurate due to interference in H→4f decay ! 1) H→ZZ→eeee,μμμμ: large enhancement on BR (+11% at MH=120GeV) due to interference in ZZ. 2) H→WW/ZZ→eνeν,μνμν: an interference effect (-5.4% at MH=120GeV) below WW/ZZ thresholds. 3) H→WW→lνqq ,H→ZZ→llqq, ννqq less than 1%, except H→WW/ZZ→qqqq at low Higgs mass. • Current LHC analyses adopt corrections for H→ZZ→eeee,μμμμ only. (H→4f NLO MC does not exist.) • Recent Prophecy4f v.2 enables weight=1 generation of H→4f decay. • Needs to investigate new MC with NLO QCD (Higgs production) + NLO QCD+EW H→4f (Higgs decay). https://twiki.cern.ch/twiki/bin/view/LHCPhysics/BRs LHC Higgs Cross Section Working Group

26. Correlated Uncertainties ATL-PHYS-PUB-2011-011 CMS NOTE-2011/005 LHC Higgs Cross Section Working Group

27. Higgs Decay Width and Mass Resolution ATL-PHYS-PUB-2011-011 CMS NOTE-2011/005 LHC Higgs Cross Section Working Group