1. Results from the LHC Higgs Cross Section WG
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 Sep. 2, CERN
Aug. 29, 2011
LHC Higgs Cross Section Working Group

2. LHC Higgs Cross Section Working Group
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.
Aug. 29, 2011
LHC Higgs Cross Section Working Group

3. 1. LHC Higgs Cross Section Working Group
ATL-PHYS-PUB
CMS-PAS-HIG
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, …
Aug. 29, 2011
LHC Higgs Cross Section Working Group

4. LHC Higgs Cross Section Working Group ATLAS ⊕ CMS ⊕ LHCb ⊗ Theory
SM XS TF
MC Group
LHC Higgs Cross Section Working Group
ATLAS ⊕ CMS ⊕ LHCb ⊗ Theory
Statistics Forum
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-bkg interf. 
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
Aug. 29, 2011
LHC Higgs Cross Section Working Group

6. Higgs Cross Section Issues
ggF, VBF, WH/ZH, ttH, BSM Higgs
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
Jet bin uncertainty
H+0,1,2-jets
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
Aug. 29, 2011
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)
(NNLO QCD)
VBF
VV2H (NLO QCD)
VBFNLO (NLO QCD)
HAWK (NLO QCD+EW)
(NNLO)
WH/ZH
V2HV (NLO QCD)
(NNLO)
ttH
HQQ (LO QCD)
bbH
(NNLO QCD)
+ private codes.
Higgs Decay
HDECAY (NLO)
Prophecy4f (NLO)
FeynHiggs, CPSuperH
gluon
W/Z
top/bottom
Higgs
Higgs pT
HqT (NLO+NNLL)
ResBos (NLO+NNLL)
W/Z
NLO MC
POWHEG,
SHERPA, HERWIG++
MCFM
PDF: MSTW2008, CT10, NNPDF2.1, etc.
Aug. 29, 2011
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
KNNLO/NLO
(KNLO/LO)
Scale
PDF+αs
Scale+PDF
ggF
+25% (+100%)
+12 -7%
±8% %
VBF
<1%
(+5-10%)
±1%
±4%
±5%
WH/ZH
+2-6%
(+30%)
ttH -
(+5-20%)
+4 -10% %
Note: Scale and PDF+αs uncertainties are handled separately according to LHC Higgs combination WG’ prescription.
(ATL-PHYS-PUB , CMS NOTE-2011/005)
Aug. 29, 2011
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: MH
Decay
THU PU
Total
120GeV
H→γγ
±2.9%
±2.5%
±5.4%
H→bb
±1.3%
±1.5%
±2.8%
H→ττ      
±3.6%
±6.1%
150GeV
H→WW
±0.3%
±0.6%
±0.9%
H→ZZ
Aug. 29, 2011
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
ggF
VBF WH ZH
ttH
MSSM
h/H/A H± VV
Wbb
Zbb
ttbar
HERWIG++/POWHEG ✔ -
H/Att
tH±
POWHEG ✔*
SHERPA/MENLOPS
* Zbb work in progress.
VBF dedicated MC: HAWK, VBFNLO
Aug. 29, 2011
LHC Higgs Cross Section Working Group

11. LHC Higgs Cross Section Working Group
Higgs pT Spectrum
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
Can we learn from Z(W), ttbar pT spectrum ?
NNLO
NLO
CERN Report
Aug. 29, 2011
LHC Higgs Cross Section Working Group

12. 4. Jet-bin Uncertainty in Exclusive Analysis
Exclusive analysis improves S/N, ex. H→WW→lνlν vs ttbar 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
Aug. 29, 2011
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.
δσ≥0
+12 -7%
δσ≥1
±20%
δσ≥2
±20% (NLO),
±70% (LO)
Which uncertainty
for 2-jet bin with
VBF topology ?
I. Stewart and F. Tackmann,
arXiv:
Aug. 29, 2011
LHC Higgs Cross Section Working Group

14. 5. Standard Model Backgrounds and Interferences
Process
Dominant Backgrounds
H→γγ
γγ, γ-jet
H→ττ
Z→ττ, top, EW, QCD
H→bb
Vbb, V+jets, top
H→WW→lνlν
WW, V+jets, top
H→WW→lνqq
H→ZZ→llll
ZZ, top, Zbb
H→ZZ→llνν
ZZ/WZ/WW, top, Z+jets
H→ZZ→llqq
MSSM ττ H±
top
Irreducible backgrounds: WW and ZZ in H→WW/ZZ→4f.
Aug. 29, 2011
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 ? … MA MB NA NB
Cut1
Cut2
ATLAS-CONF
Aug. 29, 2011
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 (4% for H+0j, 7% for H+1j) and
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, handle ‘single-resonant diagrams’.
(J.M. Campbell et al.,arXiv: ).
Double-resonant diagram only
With single-resonant diagram
← Double resonant →
Single resonant
+ many
grc(KEK) ZZ
Single-W saga for searches at LEP2
Zγ*
γ*γ*
pp→4f,6f era for LHC !
Aug. 29, 2011
LHC Higgs Cross Section Working Group

17. LO/NLO MC for qq/qg/gg→WW/WZ/ZZ
2011.8 MC
Process
Order
Double-resonant diagram
Single-resonant diagram
Zγ inter-ference
Spin corre-lation
tau polari-zation*
MCFM v6.01
qq+gg→VV*
NLO ✔
Pythia
qq→VV* LO -
LO ME Generator2
gg2WW/ZZ3
gg→VV*
HERWIG++
qq→VV
✔***
✔**
POWHEG5
SHERPA MENLOPS6
(✔)
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.
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, should allow us to study the interference gg→H→VV and SM bkg.
* Tau polarization implementation
is experiment dependent.
** Needs code hack.
*** Except ZZ.
Aug. 29, 2011
LHC Higgs Cross Section Working Group

18. LHC Higgs Cross Section Working Group
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 ?
gg→W+W-→e+νeμ-νμ
Higgs
W/Z
top/bottom
gluon
Higgs – spin 0
J.M. Campbell et al.,arXiv:
Aug. 29, 2011
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:
G. Passarino, talk given at BNL Higgs XS WS
Propagator scheme vs Breit-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
Aug. 29, 2011
LHC Higgs Cross Section Working Group

20. Fourth Generation Model
7. Beyond Standard Model Higgs
Fourth Generation Model
Unitarity argument puts MQ4< GeV.
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: ) and
decay (Prophecy4fv2) indicate very large corrections.
Full listings of numbers and figures at
Fourth Generation Model
Top/bottom
+ heavy quarks
Without NLO EW corrections
Aug. 29, 2011

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
Aug. 29, 2011
LHC Higgs Cross Section Working Group

22. LHC Higgs Cross Section Working Group
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
All information can be found at our TWiki page,
I speak Fortran.
Started to learn
PAW, and 14 TeV.
Luminosity?
I speak C++, Python and ROOT, and
7 TeV.
Scuola di Vaticani
Aug. 29, 2011
LHC Higgs Cross Section Working Group

23. LHC Higgs Cross Section Working Group
LHC2TSP Workshop
Backup
Backup
Aug. 29, 2011
LHC Higgs Cross Section Working Group

24. LHC Higgs Cross Section WG Organization
Aug. 29, 2011
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).
Aug. 29, 2011
LHC Higgs Cross Section Working Group

26. Correlated Uncertainties
ATL-PHYS-PUB
CMS NOTE-2011/005
Aug. 29, 2011
LHC Higgs Cross Section Working Group

27. Higgs Decay Width and Mass Resolution
ATL-PHYS-PUB
CMS NOTE-2011/005
Aug. 29, 2011
LHC Higgs Cross Section Working Group