Higgs phenomenology & new physics

Shinya KANEMURA(Univ. of Toyama)

KEKTH07, Dec. 13. 2007

Content of talk• Introduction

– Electroweak Symmetry Breaking– Physics of Higgs self-coupling

• Self-coupling measurement at collider experiments– LHC– ILC

• Possibility of measuring HHH at a γγ colliderγγ→ H＊→ HH

Is there any advantage in the HHH determination?Sensitivity study

• Summary

Electroweak Symmetry BreakingSM Gauge structure: SU(3)C×SU(2)I×U(1)Y

EWSB： SU(2)I×U(1)Y → U(1)EM

SM Higgs sectorA Higgs doublet

Light Higgs → Weak couplingHeavy Higgs → Strong coupling

Fields obtain masses from VEV.

Gauge interaction(Higgs mechanism)

Yukawa interaction

Mass-Coupling relation in the SM

All masses are given in proportion to the unique VEV

The SM is tested by usingthis universality

In general, this relation does not hold in extended Higgs models.

Not measured

Measure both the mass and the coupling independently!

LEP Constraint

Indirect constraint via the oblique correction

Direct search

Higgs self-coupling

• SM Higgs potential – Electroweak Symmetry Breaking

– Free parameter of the SM λ

• It is important to measure independently both the mass mh and the coupling hhh (and hhhh)– Test for the SM Higgs potential– Nature of the EWSB, – New physics determination

Hierarchy problem (Λ=1016-19GeV)

– Scenarios for NP• SUSY （boson ⇔ fermion）• Dynamical SB （Higgs = composite）• Little Higgs （Higgs=pseudo NG boson）• ….

New Physics

Radiative correction to the mass of H (spin 0)

～Λ２

Ｈ Ｈ

Strange!

But mH is O(100)GeV

It is difficult to believe that the SM holds up to very high energy.

New physics is expected to appear at TeV scales.

These models of new physics deduce a special extended Higgs sector in the low energy effective theory

New Physics effect on the HHH coupling

Effective Theory Genuine dim-6 operators

T. Han et al

Quantum Correcitons to HHH(Non-decoupling effect)

The Higgs self-coupling receives large quantum corrections

New Physics effect on the triple Higgs boson coupling

The hhh coupling is sensitive to loop effects.

New particles with similar properties also give large effects in the hhh prediction (2HDM etc)

Large deviations (several 10 % - 100%) can easily appear.

2HDM

SK, Kiyoura,Okada,Senaha,Yuan

Decoupling/Non-decoupling

Non-decoupling effect

Λ: CutoffM: Mass scale

irrelevant to VEV

New Physics Effect

MSSM

Cosmological Connections• Higgs Effective Potential• Electroweak Phase Transition

at Early Universe– SM λHHH A large δλHHH

– 2nd Order ⇔ Strong 1st Order – Electroweak Baryogenesis requires a

strong 1st Order PT (For avoiding sphaleron smearing in broken phase)

– 2HDM – Dim-6 Operator (Grogean, Sevant, Wells,)– MSSM (Nelson et al; Carena et al, …..)

SK, Okada, Senaha

⇒

Measurement of the HHH coupling

• Higgs self-coupling (HHH, HHHH)– Direct information to the Higgs potential– Effect on the New Physics– Cosmological Connection

• Measurement at collider experiments– LHC– ILC

• Alternative possibility: ILC (γγ option)• Sensitivity to anomalous deviations of λ

λ=λSM + δλ = λSM (1+ δκ)

Required accuracy

HHH measurement at LHC• Decays into gauge boson

pairs • Hopeless for a light H• Intermediate masses:

Non-vanishing of λ can be established at the LHC.

Bauer, Plehn, RainwaterPrecision measurement of the HHH coupling is

business of the ILC.

Measurement at the ILC

HH-Strahlung HH-Fusion

Two Production Mechanisms

collision

Measurement at the ILC

HH-strahlung HH-fusion

Anomalous λ dependences

Higgs potential reconstruction• Sensitivity to new physics is large in the triple Higgs

coupling (HHH). • Naively, NP effects on the quartic coupling (HHHH) is

6 times greater than those on the hhh coupling.

– Possible to measure the hhhh coupling ?– Unfortunately very challenging.

(even at a multi TeV collider)– Any idea is required.

hep-ph/0412251CLIC Physics WG

HHH measurement at the γγ collider

• We discuss a possibility to measure the Higgs tri-linear coupling via the process of

γγ→HHat the ILC photon collider option.

– Alternative or better as compared to that in the e+e-collision? Jikia, Jikia and Belusevic

– Can new physics effects on γγ→HH drastically change SM predictions?

– Valuable for a simulation study?• Study is now developing.

– The results are preliminary.

Asakawa, Harada, SK, Okada, Tsumura

Study HHH at a photon collider

Difference from ZHH and HHνν production at ILC– Loop induced process

• Theoretical interests• Direct new physics loop

contribution to the γγH (loop induced) couplings• Different δλ dependences from the e+e- collision

⇒ different sensitivity property

– Two body final state• There is kinematical advantage, even though a loop

suppression and also even though Lγγ ~ Le+e-/3

– Helicity amplitude

Process

SM diagrams

Helicity amplitudes

G.V.Jikia

Sub-Process

Sub-Process

−1 −0.5 0 0.5 1cosΘ

2.5

3.5

4.5

5.5

6.5

σ(γγ

→H

H)

(fb

)

++ Root(s)=1.5 TeVmH=730GeV

δκ=−1

−0.3

0

+0.3

+1

−1 −0.5 0 0.5 1cosΘ

0

0.04

0.08

0.12

0.16

0.2

0.24

0.28

0.32

σ(γγ

→H

H)

(fb

)

+− Root(s)=1.5TeV

mH=500GeV

450

400

Anomalous coupling parameter δκδκ does change cross sections, but does not affect angular distribution

Full Cross Section Photon structure function

Ginzburg, et. al

Full cross sections (δκ dependences)

Anomalous coupling parameter δκ

In some cases, sensitivity to δκ looks large

Full Cross Section 2

Estimation of HHH sensitivity

Estimation of HHH sensitivity• At the ILC, energies of

initial electron and laser can be changed.

• After H is found, mH is known. Then we can examine the HHH coupling by selecting the best Eee.

The best Eee for each mH

mH=160 GeV

Full Cross Section becomes large for Eee=450-500 GeV

0 0.2 0.4 0.6 0.8 1z=Wγγ/2E

0

1

2

3

dLγγ/dz

k2Lee

x=4.8

(−1,−1)

(0.−1)

(0,0)

(0,−1)

(2λ1Pc1,2λ2Pc2)

↑Eee

Photon Structure Funciton

The best Eee for each mH

mH=200GeV

Full Cross Section becomes large for Eee=550-600 GeV

0 0.2 0.4 0.6 0.8 1z=Wγγ/2E

0

1

2

3

dLγγ/dz

k2Lee

x=4.8

(−1,−1)

(0.−1)

(0,0)

(0,−1)

(2λ1Pc1,2λ2Pc2)

Photon Structure Funciton

↑Eee

New Physics effects on

– New physics loop effect can be large, because the SM contributions are also loop-induced.

– New Physics contribution changes not only the size of the cross section but also (delicate) balance between the pole and the box diagrams.

HHH sensitivity could greatly depend on the model

in new physics models

Extended Higgs models: 2HDM – additional charged scalar loop effect– non-decoupling features

Pure Dim-6 operator effects – Two operators of pure HHH dim6-coupling– Momentum dependences of the effective HHH coupling

Other models: SUSY, …– charged new particle effects

Simulation study

Complementarity with ZHH, ννHH study

Summary• Higgs self-coupling (HHH, HHHH)

– Nature of SSB (Higgs potential)– Probe of new physics

• HHH measurements– LHC: Difficult – ILC studies for ZHH, ννHH

• Possibility of measuring HHH at a γγ collider– Consistent with previous works in the SM Jikia, Belusevic– Sensitivity study for the anomalous λ coupling (Preliminary)– For mH > 150 GeV, can be useful with better sensitivity

than that at the 500 GeV e+e- collider– Backgrounds

mH=120GeV WW O(10-100) pbmH=200GeV WWWW O(10-100) fb

Reduction by invariant mass kinematic cuts and …

Backup Slide 1

Backup Slide 2• Sensitivity

HHH, HHHH Measurement at the LHC

Sub-Process 1

50 100 150 200 250mH (GeV)

10−2

10−1

100

σ(γ

γ→H

H)

(fb

)

++ Root(s)=500Ge

W−loop

mt=150GeV

top−loop

50 150 250 350 450mH (GeV)

10−2

10−1

100

σ(γ

γ→H

H)

(f

b)

W−loop

top−loop

both

++ root(s)=1000GeV

0 200 400 600 800 1000mH (GeV)

10−2

10−1

100

101

σ(γ

γ→H

H)

(f

b)

++ Root(s)=2000GeV

mt=150GeV

top−loop

W−loopboth

50 100 150 200 250mH (GeV)

10−3

10−2

10−1

100

σ(γ

γ→H

H)

(f

b)

+− Root(s)=500GeVmt=150GeV

both

top−loop

W−loop

50 150 250 350 450mH (GeV)

10−3

10−2

10−1

100

σ(γ

γ→H

H)

(f

b)

+− Root(s)=1000GeV

combined

top loop

W loop

mt=150GeV

50 250 450 650 850mH (GeV)

10−3

10−2

10−1

100

σ(γ

γ→H

H)

(f

b)

+− Root(s)=2TeV

mt=150GeV

combined

top loop

W loop

Full Cross Sections (mH, Eee dependences)