Results from the LHC Higgs Cross Section WG Reisaburo TANAKA (LAL-Orsay) On behalf of the LHC Higgs...

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


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


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 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


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.


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


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


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


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


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/

http://lpc.web.cern.ch/lpc/


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


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 !


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


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


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

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/SM4At7TeV


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

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/Fermiophobic


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

mailto:[email protected]

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CrossSections


Backup

Backup

Aug. 29, 2011

LHC2TSP Workshop


LHC Higgs Cross Section WG Organization

Aug. 29, 2011




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

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/BRs


Correlated Uncertainties

Aug. 29, 2011

ATL-PHYS-PUB-2011-011CMS NOTE-2011/005


Higgs Decay Width and Mass Resolution

Aug. 29, 2011

ATL-PHYS-PUB-2011-011CMS NOTE-2011/005

Results from the LHC Higgs Cross Section WG Reisaburo TANAKA (LAL-Orsay) On behalf of the LHC Higgs...

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Transcript of Results from the LHC Higgs Cross Section WG Reisaburo TANAKA (LAL-Orsay) On behalf of the LHC Higgs...