The Higgs: a (tentative) roadmap · 1. EWSB and Higgs particles Since v is known, the only free parameter in the SM is M H (or λ). Once M H known, all properties of the Higgs are

The Higgs: a (tentative) roadmap...

Abdelhak Djouadi(U. Paris-Sud/CERN)

1. EWSB and Higgs particles

2. The Higgs at the Tevatron and the lHC

3. Implications of a Higgs discovery

4. What if the Higgs is not found (soon)?

5. Perspectives

Sacaly 02/11/2011 Higgs: a roadmap – A. Djouadi – p.1/24

1. EWSB and Higgs particles

To generate particle masses in an SU(2) ×U(1) gauge invariant way:introduce a doublet of scalar fields Φ=(Φ

+

Φ0 ) with 〈0|Φ0|0〉 6= 0

LS =DµΦ†DµΦ−µ2Φ†Φ−λ(Φ†Φ)2

v = (−µ2/λ)1/2 = 246 GeV⇒ three d.o.f. for MW± and MZ

For fermion masses, use same Φ:LYuk=−fe(e, ν)LΦeR + ...

Residual dof corresponds to spin–0 H particle.

• The scalar Higgs boson: JPC = 0++ quantum numbers.• Masses and self–couplings from V : M2

H =2λv2,gH3 = 3M2

H

v, ...

• Higgs couplings ∝ particle masses: gHff = mf

v,gHVV = 2

M2

V

v

The Higgs unitarizes the theory:

without Higgs: |A0(vv→vv)|∝E2/v2

including H with couplings as predicted:|A0|∝M2

H/v2⇒ the theory is unitary but needs MH<∼700 GeV...

V

V

V

V H


1. EWSB and Higgs particlesSince v is known, the only free parameter in the SM is MH (or λ).

Once MH known, all properties of the Higgs are fixed (modulo QCD).

Example: Higgs decays in the SM• As gHPP ∝ mP, H will decay intoheaviest particle phase-space allowed:

• MH<∼ 130 GeV, H → bb

– H → cc, τ+τ−,gg = O(few %)– H → γγ,Zγ = O(0.1%)• MH

>∼ 130 GeV, H → WW,ZZ– below threshold decays possible– above threshold: B(WW)= 2

3, B(ZZ)= 1

3

– decays into tt for heavy Higgs• Total Higgs decay width:– very small for a light Higgs– comparable to mass for heavy Higgs

HDECAY: Kalinowski, Spira, AD ⇒

Z

t�tZZWW

gg��s�s

� ��b�b

BR(H)MH [GeV℄ 1000700500300200160130100

10.1

0.010.001

0.0001

f=t,b,c,τ

f•

H

V=W,Z

V•

H

f

f

V=W,Z

V∗•H

g/γ

g/γt•

H

�(H) [GeV℄MH [GeV℄ 1000700500300200160130100

10001001010.10.010.001


1. EWSB and Higgs particlesA major problem in the SM: the hierarchy/naturalness proble m

Radiative corrections to M2H in SM with a cut–off Λ=MNP∼MPl

fH H∆M2H ≡ ∝ Λ2 ≈ (1018 GeV)2

MH prefers to be close to the high scale than to the EWSB scale...

Three main avenues for solving the hierarchy problem:Supersymmetry: a set of new/light SUSY particles cancel the divergence.– MSSM ≡ two Higgs doublet model ⇒ 5 physical states h,H,A,H±

– very predictive: only two free parameters at tree–level ( tanβ,MA)– upper bound on light Higgs Mh

<∼130 GeV and MH,H± ≈MA<∼TeV

Extra dimensions: there is a cut–off at TeV scale where gravity sets in.– in most cases: SM–like Higgs sector but properties possibl y affected– but in some cases, there might be no Higgs at all (Higgsless m odels)....Strong interactions/compositness : the Higgs is not an elementary scalar.– H is a bound state of fermions like for the pions in QCD...– H emerges as a Nambu–Goldstone of a strongly interacting se ctor..


1. EWSB and Higgs particlesand along the avenues, many possible streets, paths, corner s...

Which scenario chosen by Nature? The LHC will/should tell!Sacaly 02/11/2011 Higgs: a roadmap – A. Djouadi – p.5/24

2. The Higgs at hadron collidersMain Higgs production channels

q�q V � � HVHiggs{strahlung �qq V �V � Hq

qVe tor boson fusion

�gg HQgluon{gluon fusion �gg H Q�Qin asso iated with Q �Q

Large production cross sections

with gg → H by far dominant process

1 fb−1⇒O(104) events@lHC

⇒O(103) events @Tevatron

but eg BR(H →γγ,ZZ→4ℓ)≈10−3

... a small # of events at the end...

pp→ttH

qq→Z H

qq→WH

qq→qqH

gg→H mt = 173.1 GeVMSTW2008

√s = 1.96 TeV

σ(pp → H + X) [pb]

MH [GeV]114 120 130 140 150 160 170 180 190 200

10

1

0.1

0.01

0.001

ppp→ ttH

qq→Z H

qq→WH

qq→qqH

gg→H

mt = 173.1 GeVMSTW2008

√s = 7 TeV

σ(ppp → H + X) [pb]

MH [GeV]500400300200180160140115

100

10

1

0.1

0.01


2. The Higgs at hadron colliders

⇒ an extremely challenging task!

• Huge cross sections for QCD processes• Small cross sections for EW Higgs signal

S/B >∼ 1010 ⇒ a needle in a haystack!• Need some strong selection criteria:– trigger: get rid of uninteresting events...– select clean channels: H→γγ,VV→ℓ– use specific kinematic features of Higgs• Combine # decay/production channels(and eventually several experiments...)• Have a precise knowledge of S and B rates(higher orders can be factor of 2! see later)• Gigantic experimental + theoretical efforts(more than 30 years of very hard work!)For a flavor of how it is complicated from thetheory side: a look at the gg → H case

pp/pp_ cross sections

√s¬ (GeV)

σ (f

b)

σtot

σbb_

σjet(ET

jet > √s¬/20)

σWσZσjet(E

T

jet > 100GeV)

σtt_

σjet(ET

jet > √s¬/4)

σHiggs (MH=150GeV)

σHiggs (MH=500GeV)

pp_

pp

Tev

atro

n

LH

C

10-1

1

10

10 2

10 3

10 4

10 5

10 6

10 7

10 8

10 9

10 10

10 11

10 12

10 13

10 14

10 15

103

104


2. The Higgs at hadron collidersLOa: already at one loop

QCD: exact NLO b : K ≈2 (1.7)EFT NLOc: good approx.EFT NNLOd: K ≈3 (2)EFT NNLLe: ≈ +10% (5%)EFT other HO f: a few %.

EW: EFT NLO: g: ≈ ± very smallexact NLO h: ≈ ± a few %QCD+EWi: a few %

Distributions : two programs j

aGeorgi+Glashow+Machacek+NanopoulosbSpira+Graudenz+Zerwas+AD (exact)cSpira+Zerwas+AD; Dawson (EFT)dHarlander+Kilgore, Anastasiou+MelnikovRavindran+Smith+van Neerven

eCatani+de Florian+Grazzini+NasonfMoch+Vogt; Ahrens et al.gGambino+AD; Degrassi et al.hActis+Passarino+Sturm+UcciratiiAnastasiou+Boughezal+PietriellojAnastasiou et al.; Grazzini

The σtheorygg→H long story (70s–now) ...

g

gHq

0

0.5

1

1.5

2

100 120 140 160 180 200

MH(GeV)

σ(pp → H+X) [pb]

NLO

N2LO

N3LOapprox.

+ N3LL

√s = 2 TeV

LO

MH(GeV)

σ(pp → H+X) [pb]

NLO

N2LO

N3LOapprox.

+ N3LL

√s = 14 TeV

LO

0

20

40

60

80

100 150 200 250 300

Moch+Vogt


2. The Higgs at hadron collidersDespite of that, the gg→H cross section still affected by uncertainties• Higher-order or scale uncertainties:K-factors large ⇒ HO could be importantHO estimated by varying scales of process

µ0/κ ≤ µR, µF ≤ κµ0

at lHC: µ0 = 12MH, κ=2 ⇒ ∆scale≈10%

• gluon PDF+associated αs uncertainties:gluon PDF at high–x less constrained by dataαs uncertainty (WA, DIS?) affects σ ∝ α2

s⇒ large discrepancy between NNLO PDFsPDF4LHC recommend: ∆pdf ≈10%@lHC• Uncertainty from EFT approach at NNLOmloop ≫ MH good for top if MH

<∼2mt

but not above and not b ( ≈10%), W/Z loopsEstimate from (exact) NLO: ∆EFT≈5%• Include ∆BR(H→X) of at most few %

total ∆σNNLOgg→H→X ≈ 20–25%@lHC

LHC-HxsWG; Baglio+AD ⇒

500300115

1.21.11.0

0.9

0.8

κ = 2

κ = 3

NNLO at µR = µF = 1

2MH

√s = 7 TeV

σ(gg → H) [pb]

MH [GeV]

500400300200150

10

1

500300115

1.0

0.9

0.8

HERAPDF(αS =0.1176)


JR09

ABKM

MSTW


2MH

√s = 7 TeV

σ(gg → H) [pb]

MH [GeV]

500400300200150

10

1

√s = 7 TeV

∆EFTσ(gg → H) [%]

MH [GeV]

350300250200150

8

7

6

5

4

3

2

1



Expectations for the future:At lHC:

√s=7 TeV and L≈ few fb−1

5σ discovery for MH≈130–200 GeV95%CL sensitivity for MH

<∼600 GeVgg→H→γγ (MH

<∼ 130 GeV)gg→H→WW→ℓνℓν + 0,1 jetsgg→H→ZZ→4ℓ,2ℓ2ν,2ℓ2bHelp from VBF/VH; gg→H→ττ?

Tevatron: some data still to be analyzednow surpassed by lHC in all channels.Still HV →bbℓX@MH

<∼130 GeV!Full LHC: same as lHC plus some others– VBF: qqH → ττ, γγ,ZZ∗,WW∗

– VH→Vbb with jet substructure tech.– ttH: H→γγ bonus, H →bb hopeless?

]2 [GeV/cH

Higgs mass, m200 300 400 500 600

) σ S

igni

fican

ce o

f Obs

erva

tion

(

0

2

4

6

8

10

12

14

16CMS Preliminary: Oct 2010

Projected Significance of Observation

@ 7 TeV -15 fb Combinedγγ

V(bb)-boosted)ττVBF(

lvlvjj (SS)→W(WW) (ll)(lv)(jj)→Z(WW)

WW(2l2v)+0j WW(2l2v)+1j

2l2v→VBF(WW) 4l→ZZ 2l2v→ZZ 2l2b→ZZ

1

10

10 2

100 120 140 160 180 200

mH (GeV/c2)

Sig

nal s

igni

fican

ce H → γ γ ttH (H → bb) H → ZZ(*) → 4 l H → WW(*) → lνlν qqH → qq WW(*)

qqH → qq ττ

Total significance

∫ L dt = 30 fb-1

(no K-factors)

ATLAS


2. The Higgs at hadron collidersHiggs production in the MSSM What is different from the SM

q�q V � � HVHiggs{strahlung

�qq V �V � HqqVe tor boson fusion

�gg HQgluon{gluon fusion �gg H Q�Qin asso iated with Q �Q

t�t�Z�W�qq�b�b�gg!�pp! H+�tb

AHh

tan� = 30ps = 14 TeV�(pp! �+X) [pb℄M� [GeV℄ 1000100

1000100

101

0.10.01

(assuming heavy sparticles)• All work for CP–even h,H bosons.– rates suppressed except for HSM

– CP: no AV and qqA processes– additional mechanism: qq → A+h/H• For Φ=h/H,A dominant processes:– gg→Φ with contribution of b–quarks– gg→Φbb or equivalent bb→Φ

(both enhanced by a power tan 2β)• For charged Higgs boson:– MH

<∼ mt: pp → tt with t→H+b– MH

>∼ mt: continuum pp → tbH−

Now@lHC for high tan β values :– h/H as in SM with Mh =115–130 GeV– H/h and A in gg,bb→Φ → τ+τ−

– H± in t→H+b with H+→τ+νSacaly 02/11/2011 Higgs: a roadmap – A. Djouadi – p.11/24


[GeV]Am

100 150 200 250 300 350 400 450

βta

n

0

10

20

30

40

50

60All channels

-1 Ldt = 1.06 fb∫ = 7 TeV, s

>0µ, maxhm

ATLAS Preliminary

Observed CLsExpected CLs

σ 1±σ 2±

LEP observed-1ATLAS 36 pb expected-1ATLAS 36 pb

Expected limit (3 fb−1)

Expected limit (1 fb−1)

Expected limit (0.5 fb−1)

Observed limit (√

s = 1.96 TeV)

Observed limit (36 pb−1)

√s = 7 TeV

σ(pp → Φ → τ+τ−)

MA [GeV]

tan

β

300250200150100

60

50

40

30

20

10

Baglio+AD



Let us assume for some time that a Higgs particle has been obse rvedby the ATLAS and CMS collaborations (un sympa. cadeau de Noel ?)...

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

CMS–HIG–11–666 CERN-PH–EP–2011–0422011/08/22

We finally got the damn Higgs particle in CMS!

..... and it weights 145 GeV...

The CMS collaboration

Abstract

A measurement of W+W− production in pp collisions at√

s = 7 TeV anda search for the Higgs boson by the CMS collaboration are reported. TheW+W− candidates are selected in events with two leptons, either electrons or

muons. The measurement is performed using LHC data recorded with theCMS detector, corresponding to an integrated luminosity of 5 fb−1. The pp →W+W− cross section is measured to be 41.1±5.3 (stat)±.8 (syst)±2.5 (lumi) pb.Something looks fishy there and it looks like there is a 5σ excess above the

standard model prediction. Some of us therefore think that we have finallyfound the Higgs boso with a 145 GeV mass (why 145? why not? it looks like agood number..) and, before the signal disappears, we are drinking champagne.

More information will be given after we finish with the hang–over...

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

ATLAS–HIG–11–111 CERN-PH–EP–2011–0432011/08/22

And the verdict is: YES, the Higgs indeed exists!

..... and it came across our detector...

The ATLAS collaboration

Abstract

A measurement of pp → ZZ production in pp collisions at√

s = 7 TeV

and a search for the Higgs boson by the ATLAS collaboration are reported.The ZZ candidates are selected in events with four leptons, either electronsor muons. The measurement is performed using LHC data recorded with the

ATLAS detector, corresponding to an integrated luminosity of 5 fb−1. Manysignal peaks show up in the 4ℓ mass range between 120 and 150 GeV and,

despite of the fact that we do not understand all backgrounds, we concludethat the siginificant excess of events can be attributed to the unfamous Higgs

particle (that half of the collaboration does not believe in...). As in the caseof our CMS collegues, we are heavily celebrating and not yet in a state to give

you more information. So please ”stay tuned”...

What would be the implications for high–energy particle phy sics?For illustration, take the examples of a mass MH≈115−145 GeV(with cross section/decay rates compatible with SM, say up t o ≈ 30%)



A triumph for the SM and high-energy physics!

Indirect constraints from high–precisionelectroweak data a ⇒ update summer 2011H contributes to RC to W/Z masses:

HW/Z W/Z

∝ απ

log MH

MW

+· · ·

Fit the EW precision measurements,one obtains MH = 92+34

−26 GeV, or

MH<∼ 161 GeV at 95% CL

compared with “observed” MH =145 GeVA very non–trivial check of SM consistency!In 1995: top discovery with mt≈175 GeVwhile best-fit in the SM is for same value:it was considered as a great achievement....

a Still some problems with AbFB (LEP),At

FB (TeV) and g−2...

Measurement Fit |Omeas−Ofit|/σmeas

0 1 2 3

0 1 2 3

∆αhad(mZ)∆α(5) 0.02750 ± 0.00033 0.02759

mZ [GeV]mZ [GeV] 91.1875 ± 0.0021 91.1874

ΓZ [GeV]ΓZ [GeV] 2.4952 ± 0.0023 2.4959

σhad [nb]σ0 41.540 ± 0.037 41.478

RlRl 20.767 ± 0.025 20.742

AfbA0,l 0.01714 ± 0.00095 0.01646

Al(Pτ)Al(Pτ) 0.1465 ± 0.0032 0.1482

RbRb 0.21629 ± 0.00066 0.21579

RcRc 0.1721 ± 0.0030 0.1722

AfbA0,b 0.0992 ± 0.0016 0.1039

AfbA0,c 0.0707 ± 0.0035 0.0743

AbAb 0.923 ± 0.020 0.935

AcAc 0.670 ± 0.027 0.668

Al(SLD)Al(SLD) 0.1513 ± 0.0021 0.1482

sin2θeffsin2θlept(Qfb) 0.2324 ± 0.0012 0.2314

mW [GeV]mW [GeV] 80.399 ± 0.023 80.378

ΓW [GeV]ΓW [GeV] 2.085 ± 0.042 2.092

mt [GeV]mt [GeV] 173.20 ± 0.90 173.27

July 2011

0

1

2

3

4

5

6

10030 300

mH [GeV]∆χ

2

Excluded

∆αhad =∆α(5)

0.02750±0.00033

0.02749±0.00010

incl. low Q2 data

Theory uncertaintyJuly 2011 mLimit = 161 GeV



The SM particle spectrum is now complete....

Not only we observed the last missing piece,we made sure that there is no 4th generationfermions which get masses through H field a:completion of LEP/SLC job with light νs...

If MH>∼130GeV, SM extrapolable to MGUT

Triviality/stability bounds on λ=M2

h

2v2 :λ≫1 coupling blows up (Landau pole)λ≪1 potential unstable (no EWSB...)Λ∼1 TeV : 70 <∼ MH

<∼ 700 GeVΛ∼MGUT : 130<∼MH

<∼180 GeVwith MH≈ 145 GeV SM OK up to MGUT

b

Ellis et al. ⇒a Constraint to be updated as EW corrections found to be large: Passarino et al...b Still some efforts for ν masses, gauge coupling unification, dark matter,...

0

1

2

3

4

120 140 160 180 200 220 240 260 280 3000

1

2

3

4

mH (GeV)

σ(gg

→H

)×B

r(H

→W

W)

(pb)

Tevatron Run II PreliminaryL ≤ 8.2 fb-1

Exp. 95% C.L. Limit

Obs. 95% C.L. Limit

±1 s.d. Exp. Limit

±2 s.d. Exp. Limit

4G (Low Mass)

4G (High Mass)

GeV) / Λ(10

log4 6 8 10 12 14 16 18

[GeV

]H

M

100

150

200

250

300

350

LEP exclusionat >95% CL

Tevatron exclusion at >95% CL

Perturbativity bound Stability bound Finite-T metastability bound Zero-T metastability bound

error bands, w/o theoretical errorsσShown are 1

π = 2λπ = λ

GeV) / Λ(10

log4 6 8 10 12 14 16 18

[GeV

]H

M

100

150

200

250

300

350



Simple models for low–energy supersymmetry dead or alive.. .• Constrained SUSY models:CMSSM : Mh

<∼ 120 GeVNUHMSSM: Mh

<∼ 130 GeVout if the Higgs is too heavy....

Buchmuller et al. ⇒• Phenomenological MSSM OK?if all parameters are (very) tunedmaximum-maximorum Mh≈140GeVright in the allowed mass range..

Allanach et al. ⇒• Extensions of the MSSM?ex. NMSSM: one extra singlet Higgsmaximum mass Mmax

h ≈142 GeVEllwanger et al. ⇒

Note: check that observed state is h!

[GeV]hM90 100 110 120 130 140

2χ

∆

0

0.5

1

1.5

2

2.5

3

3.5

4

excludedLEP

inaccessible

Theoretically

[GeV]hM90 100 110 120 130 140

2χ

∆

0

0.5

1

1.5

2

2.5

3

3.5

4

[GeV]hM90 100 110 120 130 140

2χ

∆

0

0.5

1

1.5

2

2.5

3

3.5

4

excludedLEP

inaccessible

Theoretically

[GeV]hM90 100 110 120 130 140

2χ

∆

0

0.5

1

1.5

2

2.5

3

3.5

4

1 2 5 10 20 50 tanβ

100

110

120

130

140

150

160

Mhm

ax (

GeV

)

Mt = 173.7 GeV

Mt = 178.0 GeV

Mt = 182.3 GeV

conservative bound

1 2 3 4 5 6 7 8 9 10tan β

114

116

118

120

122

124

126

128

130

132

134

136

138

140

142

mmax

[GeV]



... strong constraints if the scale of SUSY breaking is very h igh...

• Split SUSY: allow fine–tuningscalars (including H2) at high scalegauginos–higgsinos at weak scale(unification+DM solutions still OK)MH ∝ log(m/MW) >∼ 145 GeV

Bernal, Slavich, ADGiudice, Feldman, ... ⇒

• SUSY broken at the GUT scale...give up fine-tuning and everything elsestill, λ∝M2

H related to gauge cplgs

λ(m)=g21(m)+g2

2(m)

8(1 + δm)

... leading to MH =141 ± 2 GeV ...Hall+Nomura ⇒

tanβ = 50� δλ = 0

tanβ = 1� δλ = 0

m ��pole) = 173 .2 � 0 .9 GeV

m GeV

hig

gs

mass

M�

GeV

�plit �U�Y

104

106

108

1010

1012

1014

1016

110

120

130

140

150

160

170

1010

1011

1012

1013

1014

1015

1016

136

138

140

142

144

146

m�

@GeVD

MH@GeVD

A scenario that might be good for string theory, but probably not for HEP...


3. Implications of a Higgs discoveryWhat about alternative New Physics scenarios?

A few examples:• In ED scenarios:– Higgsless models ruled out...– some properties could be altered(KK or new states might contribute..)

Moreau, AD; Casagrande et al. ⇒• Composite Higgs: rates alteredMCHM4: gHpp → gHpp

√1 − ξ

EWPT prefer low ξ= fv

close to SMeasy to check unless ξ ≈ 0 (SM)...

Espinosa, Grojean, Muhlleitner ⇒•Many other scenarios can be checked:fermiophobic: pp→Hqq→γγqqgauge–phobic: gg→H →τ+τ−

4th generation with pp→H→NNDittmaier et al. LHC-HxsWG ⇒

s � 10 TeV

LHCgg � h

qq�� qq��h

MKK � 2 TeV

200 300 400 500 6000.01

0.1

1

10

100

mh �GeV�

��pb�

[GeV]HM

100 150 200 250

BR

[pb]

× σ

-310

-210

-110

1

10

210

LHC

HIGG

S XS

WG

2011

Fermiophobic = 7TeVs

γγ

(SM)γγ

γZ (SM)γZ

WW

WW (SM)

ZZ

ZZ (SM)


4. What if the Higgs is not found?

In the SM at the early stage lHC: get back to the theory predict on?

We might have been too optimistic with the cross section pred iction

total ∆σNNLOgg→H→X ≈ 20–25%@lHC

and we should maybe be more conservative about the uncertain ty?

Scale uncertainty, κ=4 leads to a ≈ 20% error...

PDFs: using another set, σ might be lower by ≈ 20%

Also a slightly larger EFT uncertainty, say ≈ 10%

⇒ a total uncertainty of 50% on the cross section

≡ a possible reduction of expected rate by factor 2

(maybe do the same excercice on the backgrounds!!)

Might save the day until next year (end of lHC run?)...

But not more: at some point H should be observed!

500300115

1.21.11.0

0.9

0.8

κ = 2

κ = 3


2MH

√s = 7 TeV

σ(gg → H) [pb]

MH [GeV]

500400300200150

10

1

500300115

1.0

0.9

0.8



JR09

ABKM

MSTW


2MH

√s = 7 TeV

σ(gg → H) [pb]

MH [GeV]

500400300200150

10

1


4. What if the Higgs is not found?In SUSY theories, there are several possibilites for early n on–observation• We are not yet in the decoupling limit:– suppressd VV couplings for both h and H– for tan β>∼1, BR(VV/bb) suppressed/enhanced⇒ discovery needs larger luminosity/energy

• We have large invisible Higgs decays:– in MSSM, h→χχ decays still possible(in non–universal scenarios in particular)– in RpV models, Higgs → JJ decays largebut new (SUSY) states might be observable...

• We have new/complicated Higgs decays:– in CPV scenarios, very light Higgs H1

– in the NMSSM, a very light CP–odd A1

⇒ dominant H →H1H1,A1A1→4b decaysbut instead other Higgses could be detected ...

But at some point, at least one Higgs or a sparticle should be o bserved!

ATLAS

LEP 2000

ATLAS

mA (GeV)

tan

β

1

2

3

4

56789

10

20

30

40

50

50 100 150 200 250 300 350 400 450 500

0h

0H A

0 +-H

0h

0H A

0 +-H

0h

0H A

00

h H+-

0h H

+-

0h only

0 0Hh

ATLAS - 300 fbmaximal mixing

-1

LEP excluded

1

2

3

4

5

6789

10

20

30

40

100 200 300 400 500 600 700 800 900 1000

MH+- (GeV)

tanβ

CPX scenario

excluded by OPAL

theoretically inaccessible

H1 → γγVBF: H1 → WWVBF: H1 → ττbbh: H1 → µµtth: H1 → bbH1 → ZZ → 4 lep.



Couplings strongly suppressed in alternative New Physics s cenarios?

A few examples where this could occur:• In ED scenarios:– HVV couplings suppressed– production rates could be altered(KK or new states might contribute..)

Moreau, AD; Casagrande et al. ⇒• Composite Higgs: rates alteredMCHM4: gHpp → gHpp

√1 − ξ

EWPT prefer low ξ= fv

close to SMbut possibility of large ξ not out...

Espinosa, Grojean, Muhlleitner ⇒• Many other scenarios are possible:fermiophobic: pp→Hqq→γγqqgauge–phobic: gg→H →τ+τ−

4th generation with pp→H→NNDittmaier et al. LHC-HxsWG ⇒

s � 10 TeV

LHCgg � h

qq�� qq��h

MKK � 2 TeV

200 300 400 500 6000.01

0.1

1

10

100

mh �GeV�

��pb�

[GeV]HM

100 150 200 250

BR

[pb]

× σ

-310

-210

-110

1

10

210

LHC

HIGG

S XS

WG

2011

Fermiophobic = 7TeVs

γγ

(SM)γγ

γZ (SM)γZ

WW

WW (SM)

ZZ

ZZ (SM)



If there is no Higgs boson at all: strongly interacting Higgs sectorWW/ZZ scattering to check it. Largest energy/luminosity ne eded !

q

q

γ, ZW+

W−

XH

S0 10 20 30 40 50 60 70

PDF

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

no higgs=200 GeVHm

SILH95% e.l.SM

±l±PDF 2jl

BallestreroFranzosiMaina


5. PerspectivesVery soon we will find the Higgs: would particle physics be “cl osed”?No! Need to check that H is indeed responsible of sEWSB (and SM -like?)

Measure its fundamental properties in the most precise way:• its mass and total decay width,• its spin–parity quantum numbers and check JPC = 0++,• its couplings to fermions and gauge bosons and check that the y areindeed proportional to the particle masses (fundamental pr ediction!),• its self–couplings to reconstruct the potential VH that makes EWSB.Possible for MH≈ 115–145 GeV as all production/decay channels useful!

ttHZH

WH

Hqq

gg→H√

s = 14 TeVσ(pp → H + X) [pb]

MH [GeV]500400300230180145120100

100

10

1

0.1Zγ

γγ

tt

ZZWW

gg

µµ

ss

cc

ττ

bb

BR(H)

MH [GeV]500400300250200145120100

1

0.1

0.01

0.001

0.0001


5. PerspectivesTechnically a challenging program (even more difficult than discovery?)

(and more difficult and necessary in some SM extensions...)• needs the highest possible energy and luminosity at the LHC• might even need to move to SLHC (in particular for H self–coup ling)• even then we will be limited by theoretical/systematical un certainties• maybe an e+e− machine such as ILC or CLIC will be necessary?Zeppenfeld et al TESLA TDR

τ τ-

-+

+

(GeV)

10

10

1

-3

-2

10-1

SM

Hig

gs

Bra

nch

ing

Ra

tio

bb

ggcc

γγ

MH

W W

100 110 120 130 140 150 160

There is still some work to do and some way to go!


Documents

The Higgs: a (tentative) roadmap · 1. EWSB and Higgs particles Since v is known, the only free parameter in the SM is M H (or λ). Once M H known, all properties of the Higgs are