Trilogy of LHC Higgs Cross Section Working Group - toward precision Higgs physics - Reisaburo Tanaka (ATLAS, LAL) on behalf of LHC Higgs XS WG Higgs Quo Vadis, Aspen, March 14, 2013 1 Trilogy of LHC Higgs XS WG Aspen 2013 - Higgs Quo Vadis Mar. 14, 2013
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Trilogy of LHC Higgs Cross Section Working Group - toward precision Higgs physics -
Aspen 2013 - Higgs Quo Vadis. Trilogy of LHC Higgs Cross Section Working Group - toward precision Higgs physics -. Reisaburo Tanaka (ATLAS, LAL) o n behalf of LHC Higgs XS WG Higgs Quo Vadis, Aspen, March 14, 2013. Contents. LHC Higgs Cross Section Working Group Higgs C ross S ections - PowerPoint PPT Presentation
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Trilogy of LHC Higgs XS WG 1
Trilogy of LHC Higgs Cross Section Working Group
- toward precision Higgs physics -
Reisaburo Tanaka (ATLAS, LAL)
on behalf of LHC Higgs XS WG
Higgs Quo Vadis, Aspen, March 14, 2013
Aspen 2013 - Higgs Quo Vadis
Mar. 14, 2013
Trilogy of LHC Higgs XS WG 2
Contents
1. LHC Higgs Cross Section Working Group
2. Higgs Cross Sections
3. Higgs Decay Branching Ratios
4. Jet-bin and Higgs pT Uncertainties
5. Interference Effects in gg→H→VV
6. NLO Monte Carlo
7. Higgs Coupling and Spin/Parity
8. BSM Higgs
Summary
Disclaimer: Experimentalist’s overview of LHC Higgs XS WG activity,
putting emphasis on current issues (with personal bias).
Special thanks to the colleagues in LHC Higgs XS WG.Mar. 14, 2013
Trilogy of LHC Higgs XS WG 3
Higgs physics at LHC Main question today: is Higgs-like signal at MH=125 GeV the SM ?
Precision Higgs PhysicsHiggs mass, coupling and JPC.
Hadron collider machine can do precision physics !
Theory uncertainty is becoming more and more important than ever before !
Finding the hint of BSM physics is prime important issue !What is the implication of 125 GeV Higgs for xMSSM scenario ?
What could be the new benchmark process for BSM Higgs searches ?EW Singlet, 2HDM, Triplets, Dilaton, Composite, etc…
VLVL scattering and unitalization issue.
LHC Higgs XS WG: currently 11 subgroupsHiggs Productions: ggF, VBF, WH/ZH and ttH
Common Issues: BR, Jets, NLO MC and PDF
Light Mass Higgs (Higgs coupling and JPC)
MSSM
Heavy Higgs / BSM
→ Need to reinforce Light Mass Higgs and BSM subgroups in particular.
Mar. 14, 2013
After talk yesterday …
Trilogy of LHC Higgs XS WG 4
Challenges for precision Higgs physicsExperimental Challenges
Clear separation of ggF, VBF, WH/ZH and ttH.
Improve Higgs mass measurements (FSR etc.)
Other decay modes than big 5: H→μμ, Zγ, invisible, HH, etc.
How to carry out BSM Higgs search? Interpret SM Higgs as background ?
What could be the target for near future improvements ?Higher-order calculations (ex. NNNLO in ggF, scale uncertainty < 5%?)
PDF measurements with LHC data (gg parton luminosity < 5%?)
Better prediction on the differential distributions in Higgs and SM bkg.
Reduction of jet-bin uncertainty, ggF in 2-jet bin (VBF) category & fat jets.
Interference effects between Higgs and SM continuum, ex. γγ, WW, ZZ.
Which tools do experimental collaborations need ?Tools for Higgs property measurements, ex. MELA/JHUGen, MadGraph5
(N)NLO MC’s for Higgs and SM backgrounds, ex. H+jj.
Support for future LHC Higgs physics program HL-LHC (14 TeV, 3 ab-1 by ~2030) on Higgs (self-)coupling.
Statistics ForumCreation 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), CERN (May, Dec. 2012)
Task: SM and MSSM Higgs Cross Section and BRs Uncertainty estimation (scale, αs, PDF, etc.)
Monte Carlo at NLO for signal and bkg. Higgs Property Measurements
BSM Higgs Scenarios
11 Working Subgroups:ggF, VBF, WH/ZH, ttH, MSSM
Light Mass Higgs, Heavy Higgs/BSMBR, Jets, NLO MC, PDF
LHC Higgs Cross Section Working GroupATLAS ⊕ CMS ⊗ Theory
Mar. 14, 2013
Trilogy of LHC Higgs XS WG 8
1. LHC Higgs Cross Section Working Group
Mar. 14, 2013
All info from https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSectionsMailing lists [email protected] (main), [email protected] (Higgs properties)
Renormalization and factorization scale uncertainty study by M. Cacciari et al. work in progress.Higher-order calculations, ex. ggF QCD scale: ±8%@NNLO → ±5%@NNNLO in few years ?PDF+αs (PDF4LHC prescription): ±8% → <5% with improvements with LHC data ?
jets, top, prompt photons and Z pT distributions contribute gluon PDF determination.
(but paradoxically, ggF is the best measure to determine gg parton luminosity around MH=125GeV!)
Subdivide nuisance parameters until they become uncorrelated.
Take Gaissian/Log-normal for pdf. Practically Gaussian as κ 1.0 for scale.≃
New method by M. Cacciari and N. Houdeau. JHEP 09 (2011) 039
Preserves both characteristics of log-normal (tail) and flat-top.
Treats renormalization scale only, factorization scale is work in progress.
Questions are flat-top width and tail length.
Mar. 14, 2013
Gaussian/log-normal
log-Cacciari-Houdeau
log-double-Fermi-Diracto smoothen the edges(used in ATLAS-CONF-2013-034 )
Trilogy of LHC Higgs XS WG 14
PDF+αs uncertaintyCurrently assume separate gg-initiated ±8% and qq-initiated ±4%.
Assumes NO PDF+αs correlation between (ggF, ttH, tt, …) and (VBF, VH, VV, …).
Full correlation study in CERN Report 2 (https://cds.cern.ch/record/1416519)ggF – VBF ρ=-0.6 … due to sum rule of Σ(gg+qq+qqbar)=1.ggF – WH ρ=-0.2 … due to small correlation between gg vs qqbar.ggF – ttH ρ=-0.2 … it's the different Bijorken-x.
All these issues should be discussed in LHC Higgs Combination WG.Mar. 14, 2013
Proposal for theory uncertainty statistical treatment
Long debate on QCD scale + PDF+αs uncertainty handling.
We suggest to separate either 1) theory uncertainty (THU) or 2) parametric uncertainty (PU).
Statistical nature of THU behavior is unknown while PU is believed to behave as Gaussian (or log-normal) due to central limit theorem after many measurements. Such example is PDF+αs uncertainty.
Mar. 14, 2013
Source of theory uncertainties
QCD scale ±8% for ggF, ±1% for VBF/VH, +4-9% for ttH flat-prior
PDF+αs ±8% for gg-initiated and ±4% for qq-initiated Gaussian
BR uncertainty ±2-4% for THU±2-3% for PU
flat-prior for THU Gaussian for PU
Higgs pT mixture of missing higher-order correction (ex. NLO EW), QCD scale, PDF+αs, UE, etc.
flat-prior to be conservative
jet-bin uncertainty inclusive 0,1,2-jet bin uncertainty is σ≥0 (±10%), σ≥1 (±20%), σ≥2 (±20-30%, NLO)
flat-prior
underlying event ±10% for ggF+2j and ±3% for VBF flat-prior
shape uncertainty in bkg. estimation
ex. Z+jets bkg., WW/ZZ bkg. etc. flat-prior
Trilogy of LHC Higgs XS WG 16
HL-LHC & HE-LHC
Higgs cross sections for HE-LHC (33TeV) for ggF, VBF, WH/ZH and ttH.QCD scale uncertainty does not change compared to 7/8 TeV.
PDF+αs uncertainty also does not change much compared to 7/8 TeV.
Cross section is predictable via parton luminosity ratio.Ex. ggF is at the same MX in gg ratio, VBF MX+few hundred GeV in qq ratio.
Cross sections for Higgs self-coupling … core of future Higgs physics at LHC !
3. Higgs Decay Branching RatiosUse HDECAY and Prophecy4f for best estimate.
What are the theory (THU) + parametric (PU) uncertainties ?
Relatively large uncertainties for H→ττ, μμ, γγ, Zγ/WW/ZZ at low MH.
Smaller uncertainties relative to scale and PDF+αs uncertainties in Higgs production.
Mar. 14, 2013
MH Decay THU PU Total
120GeV H→bb ±1.3% ±1.5% ±2.8%
H→ττ
±3.6% ±2.5% ±6.1%
H→μμ ±3.9% ±2.5% ±6.4%
H→γγ ±2.9% ±2.5% ±5.4%
H→Zγ ±6.9% ±2.5% ±9.4%
H→ZZ ±2.2% ±2.5% ±4.8%
H→WW ±2.2% ±2.5% ±4.8%
A. Denner et al., Eur. Phys. J. C (2011) 71
Updated numbers in CERN Report 2.https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CERNYellowReportPageBR2Major change was BR(H→ss) due to quark mass definition.
Separation of BR THU and PU are in progress.Stick to THU+PU ±5-10% conservative uncertainty.
σ(ggF+VBF+VH+ttH) -2%/GeV (slower change in VBF than ggF)
Br(H→bb, ττ) -3%/GeV
Br(H→γγ) ±0%/GeV
Br(H→WW,ZZ) +10%/GeV
μ=(σ×BR)obs /(σ×BR)SM
ΔMH=2GeV
Large MH dependence in σ×BRin H→WW, ZZ as BR is changing rapidly.
Trilogy of LHC Higgs XS WG 19
Huge cancellation in fixed-order calculation between K-factor (σtot) and large Sudakov log (σ≥1jet).
So far we have been following the Stewart&Tackmann prescription.Conservative approach by assuming the n-jet inclusive cross section σ≥n-jet
uncertainties are uncorrelated in perturbation theory.
Recent proposal by G. Salam et al.Use jet-veto efficiency (indep. from σtot)
K-factor cancels in ε=σ0-jet/σtot
NNLO+NNLL for 0-jet bin uncertainty
is ±15%→±9% ! (code JetVHeto)
Work in progress for 1-jet bin.
Works by R. Boughezal et al. arXiv:1302.6216
4. Jet-bin Uncertainty
Mar. 14, 2013
A. Banfi et al., PRL 109 (2012) 202001
Focal points: 1. reduction in jet-bin uncertainty for 1-jet exclusive in particular,2. ggF+2-jets contamination in VBF category, how to reduce contamination and asso. uncert.,3. developments for other categorization methods rather than jet-binning, how to avoid soft-gluon.
Trilogy of LHC Higgs XS WG 20
Higgs pT UncertaintyHiggs pT in ggF is an important discriminant variable against VBF and SM backgrounds.
Theory uncertainty in Higgs pT
Acceptance uncertainties (Higgs pT), event migration between different categories.
Non-perturbative effects (Hadroniztion, UE).
POWHEG ggF has finite quark-mass effect plus Higgs pT tuned to HqT2 (hfact=MH/1.2). Thus NO MC reweighting has been necessary.
Recent discussions on Higg pT uncertainty due to finite quark-mass effect with t/b.
Assign ±10% uncertainty on Higgs pT in ggF due to finite quark-mass effect ?
We should consider Higgs Higgs pT uncertainty in other channels as well in VBF, WH/ZH and ttH, due to missing HO corrections (ex. NLO EW), QCD scale, PDF+αs, etc.
Mar. 14, 2013
Trilogy of LHC Higgs XS WG 21
5. Interference Effects in gg→H→VVInterference between gg→H→γγ, WW, ZZ and SM background continuum
gg→H→γγ: few % effect for light Higgs after experimental cuts (L. Dixon)
gg→H→WW: -10% negative interference for light Higgs and large positive for heavy Higgs. (MCFM by K. Ellis et al., gg2WW by N. Kauer).
For light Higgs, the interference can be suppressed via transverse mass cut MT<MH.
gg→H→ZZ: similar situation as H→WW but smaller interference.Now prescription exists for heavy Higgs analysis !
Higgs mass shift +150MeV in H→γγ ? S. Martin, PRD 86 (2012) 073016
Now under investigation by L. Dixon, D. de Florian for H→γγ and N. Kauer for H→ZZ*.
cf. (ATLAS-CONF-2013-014)
Mar. 14, 2013
G. PassarinoN. Kauer, G. Passarino, JHEP 1208 (2012) 116
Higgs discovery by theorist !
Trilogy of LHC Higgs XS WG 22
Interference Effects in Higgs DecayInterference in Higgs decay (→ use Prophecy4f !)
H→ZZ→e+e-e+e- or μ+μ-μ+μ- (+11%@MH=120GeV) … corrected in the analysis.
H→WW/ZZ→e+νe-ν, μ+νμ-ν (-5.4%@MH=120GeV) … not corrected as no H→4f MC!
Interference in SM bkg. qq/gg→ZZ→e+e-e+e- or μ+μ-μ+μ- also exists.Mar. 14, 2013
Ratio between approximation with PDG Br(V→ff) and Prophecy4f (with interference)
Trilogy of LHC Higgs XS WG 23
6. NLO Monte CarloMany progresses in (N)NLO Monte Carlos
Higgs signalPOWHEG MINLO
Proposal: Replace current POWHEG H+PYTHIA with new MINLO HJ to achieve NLO in both H inclusive and H+J distributions. NNLO accuracy can be achieved via weighting.
Use new MINLO HJJ when 2-jets are strictly required (i.e. VBF analysis).
Note: neither finite-quark mass nor HqT tune is done in MINLO HJ currently.
Higgs decay with Prophecy4f (can be embedded in Higgs NLO MC with NWA)Important step towards precision Higgs physics with NLO QCD+EW corrections, FSR effect, interference effect, off-shell gauge boson effect, etc. H→4f physics at LHC !
SM backgroundsγγ: 2γNNLO
V+jets: ALPGEN, BlackHat for V+4-jets (V+5+jets in progress)
SHERPA, POWHEG(MINLO) for V+0,1,2-jets
VV+jets: POWHEG-BOX WWjj(EW), how about ZZjj?
Vbb: POWHEG-BOX Wbb, how about Zbb?
BSM HiggsAim MadGraph5 as platform for BSM Higgs MC (aside Higgs JPC study)
Higgs pT in MSSM Higgs (finite quark mass effect, t/b+interference)
Mar. 14, 2013
K. Hamilton et al., JHEP 10 (2012) 155 (arXiv:1206.3572), arXiv:1212.4504