results from the lhc higgs cross section wg reisaburo tanaka (lal-orsay) on behalf of the lhc higgs...
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LHC Higgs Cross Section Working Group 1
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
Aug. 29, 2011
LHC2TSP
LHC Higgs Cross Section Working Group 2
Contents
1. LHC Higgs Cross Section Working Group
2. Higgs Cross Sections and Branching Ratios
3. NLO Monte Carlo and Higgs pT Distribution
4. Jet-bin Uncertainty in Exclusive Analysis
5. Standard Model Backgrounds and Interferences
6. Heavy Higgs Line Shape
7. 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
Aug. 29, 2011
CMS-PAS-HIG-11-022
How the LHC Higgs Cross Section WG contributed and what will do for the future ?
Higgs boson search in three directions.1) Light Higgs MH < 140 GeV H→γγ,bb,ττ,WW,ZZ JPC, Yukawa, H self-
coupling2) Heavy Higgs MH > 500 GeV H→WW,ZZ JPC, HVV, VLVL
scattering3) BSM Higgs MSSM, NMSSM, Composite, Higgsless, …
ATL-PHYS-PUB-2011-135
4
PDF4LHCWG
LHC Higgs Combination
WG
SM XS TFMC Group
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)
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 Cross Section Working GroupATLAS ⊕ CMS ⊕ LHCb ⊗ Theory
LHC Higgs Cross Section Working Group 5
LHC Higgs XS WG CERN Report
Aug. 29, 2011
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 authors151 pages370 references
LHC Higgs Cross Section Working Group
Higgs pT
(soft gluon resummation)
Higgs Cross Section Issues
Higgs Cross Sections(inclusive/exclusive)
Differential K-factors(effect of jet-veto etc.)
QCD correction NkLO + NmLLEW correction, Mixed QCD-EW
Heavy Higgs Line ShapeSM Backgrounds & Interferences
6
PDF+αs uncertaintiesRenormalization/Factorization scale dependence
Higgs decayBranching ratios(QCD/EW corr.)
gluon
top/bottom
Higgs
W/Z
W/Z
Jet bin uncertaintyH+0,1,2-jets
new quarks
ggF, VBF, WH/ZH, ttH, BSM Higgs
Aug. 29, 2011
LHC Higgs Cross Section Working Group
Tools for Higgs Physics
Higgs
W/Ztop/bottom
W/Z
7
PDF: MSTW2008, CT10, NNPDF2.1, etc.
Higgs DecayHDECAY (NLO)Prophecy4f (NLO)FeynHiggs, CPSuperH
Higgs pT
HqT (NLO+NNLL)ResBos (NLO+NNLL)
NLO MCaMC@NLO, POWHEG,SHERPA, HERWIG++MCFM
ggF, VBF, WH/ZH, ttH, MSSM Higgs
gluon
Aug. 29, 2011
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)
VBFVV2H (NLO QCD)VBFNLO (NLO QCD)HAWK (NLO QCD+EW)VBF@NNLO (NNLO)
WH/ZHV2HV (NLO QCD)VH@NNLO (NNLO)
ttHHQQ (LO QCD)
bbHbbH@NNLO (NNLO QCD)
+ private codes.
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).
KNNLO/NLO
(KNLO/LO)Scale PDF+αs
Scale+PDF
ggF +25% (+100%)
+12 -7% ±8% +20 -15%
VBF <1%(+5-10%)
±1% ±4% ±5%
WH/ZH +2-6%(+30%)
±1% ±4% ±5%
ttH -(+5-20%)
+4 -10% ±8% +12 -18%
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)
Aug. 29, 2011
K-factor, QCD scale and PDF uncertainties at 7TeV
LHC Higgs Cross Section Working Group 9
Higgs Decay Branching Ratios
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% ±2.5% ±6.1%
150GeV H→WW ±0.3% ±0.6% ±0.9%
H→ZZ ±0.3% ±0.6% ±0.9%
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.
Aug. 29, 2011
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.
Aug. 29, 2011
ggF VBF WHZH
ttH MSSMh/H/A
MSSMH±
VV WbbZbb
ttbar
HERWIG++/POWHEG ✔ ✔ ✔ - - - ✔ - -
(a)MC@NLO✔ - ✔ ✔ H/Att tH±
✔ ✔ ✔
POWHEG✔ ✔ - ✔ - - ✔ ✔* ✔
SHERPA/MENLOPS ✔ - ✔ - - - ✔ - -
VBF dedicated MC: HAWK, VBFNLO* Zbb work in progress.
2011.8
11
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 MC@NLO.
Can we learn from Z(W), ttbar pT spectrum ?
CERN Report 2011-002
NNLO
NLO
Aug. 29, 2011 LHC Higgs Cross Section Working Group
LHC Higgs Cross Section Working Group 12
4. Jet-bin Uncertainty in Exclusive AnalysisExclusive 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.
Aug. 29, 2011
C. Anastasiou et al., JHEP 0709 (2007) 018 ATLAS-CONF-2011-134
The reduction in scale variation for small pT is artificial because of cancellations between large K-factors and large logarithms.
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:
Aug. 29, 2011
I. Stewart and F. Tackmann, arXiv:1107.2117
LHC Higgs Cross Section Working Group
δσ≥0 +12 -7%
δσ≥1 ±20%
δσ≥2 ±20% (NLO), ±70% (LO)
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 withVBF topology ?
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 WW, V+jets, top
H→ZZ→llll ZZ, top, Zbb
H→ZZ→llνν ZZ/WZ/WW, top, Z+jets
H→ZZ→llqq ZZ/WZ/WW, top, Z+jets
MSSM ττ Z→ττ, top, EW, QCD
H± top
Aug. 29, 2011 LHC Higgs Cross Section Working Group
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 EstimationKeyword = ‘Data driven background estimation’
ABCD methodAssume 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 ?
…Aug. 29, 2011
MA MB
NA NB
Cut1
Cut
2
ATLAS-CONF-2011-134
LHC Higgs Cross Section Working Group 16
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’.
Double-resonant diagram only
With single-resonant diagram
Effect of Single-Resonant Diagrams
← Double resonant → Single resonant+ many grc(KEK)
Aug. 29, 2011
Zγ*ZZ
γ*γ*
(J.M. Campbell et al.,arXiv:1107.5569).
Single-W saga for searches at LEP2
pp→4f,6f era for LHC !
LHC Higgs Cross Section Working Group 17
LO/NLO MC for qq/qg/gg→WW/WZ/ZZ
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 qq→VV* LO ✔ ✔ ✔ ✔ -
gg2WW/ZZ3 gg→VV* LO ✔ - ✔ ✔
HERWIG++ qq→VV NLO ✔ - - ✔ ✔
MC@NLOv4 qq→VV NLO ✔ - - ✔*** ✔**
aMC@NLO4 qq+gg→VV* NLO ✔ ✔ ✔ ✔ ✔**
POWHEG5 qq→VV* NLO ✔ ✔ ✔ ✔ ✔**
SHERPA MENLOPS6 qq→VV* NLO ✔ ( )✔ ( )✔ ✔
1. MCFM: v6.1 will contain the gg→WW with a massive top in the loop.2. LO ME MC like CompHEP/Grace/MadGraph/Phantom/Sherpa/WHIZARD/etc. are also useful.3. gg2WW/ZZ: The gg→H→VV and continuum interference is now in gg2WW and will be in gg2ZZ.4. aMC@NLO: Now available for qq→WW/WZ/ZZ at NLO and also gg→WW/ZZ (still private).5. POWHEG: WW/WZ/ZZ exist. Does not include gg→VV*, thus one needs to use gg2WW/ZZ or others.6. 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.
Aug. 29, 2011
Current ‘champs de bataille’ !
2011.8
LHC Higgs Cross Section Working Group
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 ?
6. Heavy Higgs Line Shape
18
Higgs
W/Z
top/bottom
gluon
W/ZHiggs – spin 0
Aug. 29, 2011
J.M. Campbell et al.,arXiv:1107.5569
gg→W+W-→e+νeμ-νμ
19
Heavy Higgs Cross Section and Line Shape
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.
Aug. 29, 2011
C. Anastasiou et al., arXiv:1107.0683
Seymour Defalut
LHC Higgs Cross Section Working Group
Large distortion in Higgs invariant mass spectrum for heavy Higgs.
MH=600GeV MH=800GeV
Top/bottom+ heavy quarks
Without NLO EW corrections
Fourth Generation Model
Aug. 29, 2011
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
7. Beyond Standard Model Higgs
LHC Higgs Cross Section Working Group 21
Fermiophobic Higgs ModelAssume 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%.
Aug. 29, 2011
Excess over SM for MH<120GeV
Full listings of numbers and figures at https://twiki.cern.ch/twiki/bin/view/LHCPhysics/Fermiophobic
HDECAY version 4.00
LHC Higgs Cross Section Working Group 22
SummaryLHC 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.
FutureComplete 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 [email protected].
All information can be found at our TWiki page,
https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections.
Aug. 29, 2011
I speak Fortran.Started to learn PAW, and 14 TeV.
Luminosity?I speak C++, Python and ROOT, and 7 TeV.
Scuola di Atene@Musei Vaticani
LHC Higgs Cross Section Working Group 23
Backup
Backup
Aug. 29, 2011
LHC2TSP Workshop
LHC Higgs Cross Section Working Group 24
LHC Higgs Cross Section WG Organization
Aug. 29, 2011
https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections
LHC Higgs Cross Section Working Group 25
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).
Interference in H→WW/ZZ→4f Decay
Aug. 29, 2011
https://twiki.cern.ch/twiki/bin/view/LHCPhysics/BRs
LHC Higgs Cross Section Working Group 26
Correlated Uncertainties
Aug. 29, 2011
ATL-PHYS-PUB-2011-011CMS NOTE-2011/005
LHC Higgs Cross Section Working Group 27
Higgs Decay Width and Mass Resolution
Aug. 29, 2011
ATL-PHYS-PUB-2011-011CMS NOTE-2011/005