Trilogy of LHC Higgs Cross Section Working Group - toward precision Higgs physics -

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


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


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 …


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.

Further study for HE-LHC (33 TeV or above?).

Mar. 14, 2013

Trilogy of LHC Higgs XS WG

Higgs pT

(soft gluon resummation)

Higgs Physics Theoretical 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

Higgs Mass, Coupling and JPC

5

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 particles

ggF, VBF, WH/ZH, ttH, BSM Higgs

Mar. 14, 2013

Trilogy of LHC Higgs XS WG

Tools for Higgs Physics

Higgs

W/Ztop/bottom

W/Z

6

PDF: MSTW2008, CT10, NNPDF2.1, etc.

Higgs DecayHDECAY (NLO)Prophecy4f (NLO)

Higgs pT

HqT (NLO+NNLL)ResBos (NLO+NNLL)

NLO MCaMC@NLO, POWHEG,SHERPA, HERWIG++MCFM

ggF, VBF, WH/ZH, ttH, BSM Higgs

gluon

Mar. 14, 2013

Cross Section

ggF HIGLU (NNLO QCD+NLO EW)iHixs (NNLO QCD+NLO EW)FeHiPro (NNLO QCD+NLO EW)HNNLO, HRes (NNLO+NNLL 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.

Higgs PropertiesMELA/JHU, MEKDMadGraph5

Jet-vetoJetVHeto

MSSMFeynHiggs, SusHi2HDMC, CPSuperH


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), 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


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)

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

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

mailto:[email protected]




Trilogy of LHC Higgs XS WG’s CERN Report

Mar. 14, 2013

CERN Report 1 went out before the 1st Higgs results of LHC !(facilitated the comparison and combination, appreciated by the collaborations)

64 authors151 pages370 references

120 authors275 pages456 references


Trilogy of LHC Higgs XS WG’s CERN Report

Mar. 14, 2013

CERN Report 3 to be completed by late spring 2013 !


2. Higgs Cross SectionsOfficial numbers for Higgs cross sections at 7 and 8 TeV and spread sheet at

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CERNYellowReportPageAt7TeV


Now ggF and VBF cross sections with complex-pole-scheme (CPS) for entire mass range both at 7 and 8 TeV. WH/ZH and ttH in ZWA.

Always compared with two independent calculations, ex. dFG vs ABPS for ggF.

Assume factorization between QCD and EW radiative corrections.

QCD scale uncertainties, ex. ggF 1/2MH < μR,μF < 2MH (1//2 < μR/μF < 2)

7&8 TeV scan points in CERN Report 3

Mar. 14, 2013






Higgs cross section theory uncertainties

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!)

K-factor, QCD scale and PDF uncertainties

7 TeV 8 TeVKNNLO/NLO

(KNLO/LO) Scale PDF+αs

Scale+PDF Scale PDF+αs

Scale+PDF

ggF +25% (+100%) +7-8% ±8% ±15% +7-8% ±8% ±15%

VBF <1%(+5-10%) ±1% ±4% ±5% ±1% ±4% ±5%

WH/ZH

+2-6%(+30%) ±1% ±4% ±5% ±1% ±4% ±5%

ttH -(+5-20%) +3 -9% ±8%

+12 -18%

+4 -9% ±8%+12 -17%

MH=125 GeV

Mar. 14, 2013


QCD scale uncertaintyLHC Higgs combination WG’s prescription (ATL-PHYS-PUB-2011-011, CMS Note-2011/005)

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 )


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

Table 10

https://cds.cern.ch/record/1416519


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


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 !

gg → HH (HHH), qq → qqHH, WHH/ZHH

Mar. 14, 2013

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/HiggsEuropeanStrategy2012




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.

https://twiki.cern.ch/twiki/bin/view/LHCPhysics/CERNYellowReportPageBR2


Frequently asked question: which MH for μ ?

Mar. 14, 2013

ATLAS-CONF-2013-014Update → Aaron’s talk

Process [email protected]

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.


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.


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


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 !


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)


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

http://arxiv.org/abs/arXiv:1206.3572

http://arxiv.org/abs/arXiv:1212.4504


7. Higgs Coupling and Spin/ParityHiggs coupling measurement → talk by G. Weiglein

How to go beyond LO coupling definition with EFT ? (post interim, arXiv:1209.0040)

Higgs tensor structure JPC → talk by M. Grazzini

Consistent framework in JHU, HAWK/VBFNLO and MadGraph5 on 0±, 1±, 2±.MadGraph5 as versatile tool for Higgs (NLO MC, ggF/VBF/WH/ZH/ttH, spin corr.).

Current LHC data already disfavor 0-, 1±, 2±.

The next step would be CP-mixture and CP-violation in 0±.1. For CP mixture with interference, which benchmark model with which coupling ?

2. Which MC tools are available, JHU@CMS, MadGraph5, MEKD@CMS, etc. ?

3. What mixing observables we should measure as sensible variables, ex ΔΦZZ ?

Mar. 14, 2013

MadGraph5


8. BSM HiggsATLAS and CMS need the good benchmark scenario for BSM Higgs searches on top of SM-like Higgs signal at Mh=125 GeV.

Currently discussed are MSSM, 2HDM, EW singlet models.

MSSMNew proposed scenarios:

mhmod+, mh

mod-, light stop.

2HDMNew ATLAS results in H→WW in Type-I,II. (ATLAS-CONF-2013-027)

Used SusHi by reweighting SM Higgs XS with (α,β,MH) parametrization.

Needs to come to agreement on baseline models in Type-I,II,III,IV …

Mar. 14, 2013

M. Carena et al. arXiv:1302.7033


Summary

Two prominent pillars for Higgs physics at LHC for Higgs Quo Vadis.1. Precision measurements on Higgs properties of couplings and spin/parity.

2. Direct searches for the signature of BSM Higgs on top of 125 GeV signal.

Theory uncertainties are already becoming non-negligible !Experimental accuracy Δμ(σ/σSM)=±15% (roughly ±10% for both stat.&syst.).

Theory uncertainty is O(±10-15%) dominated by QCD scale and PDF+αs in ggF.

Future improvements in NNNLO prediction in ggF, PDF, Higgs pT, etc.

Important jet issues: reduction of uncertainty in 1-jet bin, ggF+2-jets vs VBF.

Clean separation of ggF, VBF, WH/ZH and ttH is the essential.

Many challenging issues for both EXP and TH for Higgs physics at LHC !

Mar. 14, 2013

Documents

Trilogy of LHC Higgs Cross Section Working Group - toward precision Higgs physics -