HIGGS RATES AND NEW QUARKS Elisabetta Furlan Brookhaven National - - PowerPoint PPT Presentation

HIGGS RATES AND NEW QUARKS

Elisabetta Furlan

Brookhaven National Laboratory

Galileo Galilei Institute, June 6 2013

In collaboration with S. Dawson and I. Lewis

MOTIVATION

LHC experiments: “habemus Higgs!” “a light fundamental scalar is not natural”: the hierarchy problem many extensions of the Standard Model introduce new particles that can alter the LHC phenomenology (supersymmetry, extra dimensions, little/composite Higgs models,...)

direct production loop effects

Q

x ¯ x

W − W +

t

¯ t

t ¯ t

constraints from

➡ direct searches ➡ effects on loop mediated processes

(S, T, U parameters, )

➡ measured Higgs rates!

Z → b¯ b

MOTIVATION

e+

e− q

¯ q

σ σSM = 1.4 ± 0.3 σH→γγ σSM

H→γγ

=

(ATLAS) (CMS)

( (

x ¯ x

W − W +

t

¯ t

t ¯ t

1.7 ± 0.3 0.88 ± 0.21 0.8 ± 0.3 1.1 ± 0.3

the new particles typically

✦ couple to the Higgs boson ✦ mix with the Standard Model top quark,

modifying its coupling to the Higgs boson

➡ can significantly affect Higgs production and

decays

MOTIVATION

SM4,

SM4

σCH σSM ξ = v2/f 2

composite Higgs

gg → h gg, q¯ q → ht¯ t qq → hqq q¯ q → hW, hZ

the new particles typically

✦ couple to the Higgs boson ✦ mix with the Standard Model top quark,

modifying its coupling to the Higgs boson

➡ can significantly affect Higgs production and

decays

➡ but.. do they have to? ➡ if they do, can we use these effects to learn

something about their properties?

MOTIVATION

idea:

✦ up to dimension six, there are only two operators

that describe the effective gluon-Higgs interaction

MOTIVATION

• A. Pierce, J. Thaler, L.-T. Wang, JHEP 0705:070, 2007

✦ they are related to different mass generation

mechanisms

• renormalizable (SM)
• dimension 6
• not present in the SM

MOTIVATION

✦ they contribute differently to Higgs single and pair

production

➡ combine this two channels to gain insights on the

nature of the mass of the new heavy quarks

O1 ∝Ga

µνGa,µν

✓H v + H2 2v2 ◆ O2 ∝Ga

µνGa,µν

✓H v − H2 2v2 ◆

• A. Pierce, J. Thaler, L.-T. Wang, JHEP 0705:070, 2007

single and pair Higgs production

✦ approximate leading order results

vector singlet

✦ the model ✦ experimental bounds ✦ Higgs phenomenology

OUTLINE

chiral mirror families

✦ the model ✦ experimental bounds ✦ Higgs phenomenology

gluon-Higgs effective operators

main mechanism: gluon fusion for heavy ( ) quarks, the leading order amplitude depends on the mass and the Yukawa coupling as

➡ neglecting finite-mass effects,

SINGLE HIGGS PRODUCTION

mq

2mq >mH

In the SM

✓ ◆

yqq

Agg→H ∝ X

q

yqq mq 2 3 + 7 45 m2

H

4m2

q

+ . . .

• Agg→H

ASM

gg→H

= X

q

yqq mq

ytt = mt

Standard Model like contributions NEW at leading order, the amplitude is known with the full mass dependance

in the infinite quark mass approximation,

➡ neglecting finite-mass effects,

g g qi qi qi qi H H

t t t g g H H H

g g qi qi qi H H

g g H H fi fj fi fi

g g qi qi qi qj H H

DOUBLE HIGGS PRODUCTION

yii yij

Abox,ij

gg→HH ∝

y2

ij

mimj Atri

gg→HH ∝ − 3m2 H

s − m2

H

yii mi Abox,ii

gg→HH ∝ y2 ii

m2

i

Abox

gg→HH

Abox,SM

gg→HH

= X

i,j

y2

ij

mimj

Glover, van der Bij, NPB309:282, 1988

these approximate results are useful to understand the source of the (potential) deviations from the SM in our analysis we will use the “exact” cross section

✦ for single Higgs production, through NNLO

HIGGS PRODUCTION

ihixs Anastasiou, Bülher, Herzog, Lazopoulos

EF , JHEP 1110 (2011) 115

Graudenz, Spira, Zerwas, PRL70, 1372 (1993) Spira, Djouadi, Graudenz, Zerwas, NPB453, 17 (1995) Harlander, Kilgore, PRL88, 201801 (2002) Anastasiou, Melnikov, NPB646, 220 (2002) Ravindran, Smith, van Neerven, NPB665, 325 (2003)

these approximate results are useful to understand the source of the (potential) deviations from the SM in our analysis we will use the “exact” cross section

✦ for single Higgs production, through NNLO ✦ for double Higgs production, at LO with full mass

dependence

HIGGS PRODUCTION

Glover, van der Bij, NPB309:282, 1988

mass eigenstates of mass

VECTOR SINGLET

introduced for example in little Higgs and composite Higgs models notation the fermion mass terms are

T 2

L , T 2 R

ψL = ✓T 1

L

B1

L

◆ , T 1

R , B1 R

SM-like chiral fermions vector singlet with Y=1/ 6 t, T, b = B1

mt, MT , mb

−LS

M = λ1ψLHB1 R + λ2ψL ˜

HT 1

R + λ3ψL ˜

HT 2

R + λ4T 2 LT 1 R + λ5T 2 LT 2 R + h.c.

−LSM

M

}

VECTOR SINGLET

the fermion mass terms are the charge 2/3 mass eigenstates are an admixture of and , the term can be rotated away by a redefinition of the right handed fields  4 independent parameters

−LS

M = λ1ψLHB1 R + λ2ψL ˜

HT 1

R + λ3ψL ˜

HT 2

R + λ4T 2 LT 1 R + λ5T 2 LT 2 R + h.c.

T 1 T 2 T

2 LT 1 R

t, T

✓ti Ti ◆ = ✓ci −si si ci ◆ ✓T 1

i

T 2

i

◆

ci = cos(θi) , si = sin(θi)

(i = L, R)

(mb, mt, MT , θL)

Contribution to the Peskin-Takeuchi S, T, U parameters

CONSTRAINTS

0.0 0.1 0.2 0.3 0.4 10-6 10-5 10-4 0.001 0.01 0.1 1 DSapp DUapp DTapp DS DU DT

sL

}

mb → 0 , MT >> mt

∆Sapp = − Nc 18π s2

L

⇥ log r

• 1 − 3c2

L

• + 5c2

L

⇤ ∆Tapp = TSMs2

L

• rs2

L + 2c2 L log r − 1 − c2 L

• ∆Uapp = Nc

18π s2

L

• 3s2

L log r + 5c2 L

• r = (MT /mt)2

MT = 1 TeV

Contribution to the Peskin-Takeuchi S, T, U parameters

CONSTRAINTS

}

∆Sapp = − Nc 18π s2

L

⇥ log r

• 1 − 3c2

L

• + 5c2

L

⇤ ∆Tapp = TSMs2

L

• rs2

L + 2c2 L log r − 1 − c2 L

• ∆Uapp = Nc

18π s2

L

• 3s2

L log r + 5c2 L

• r = (MT /mt)2

600 800 1000 1200 1400 1600 10-5 10-4 0.001 0.01 0.1 DS , sL = 0.01 DU , sL = 0.01 DT , sL = 0.01 DS , sL = 0.1 DU , sL = 0.1 DT , sL = 0.1

MT

decoupling occurs for

DECOUPLING

−LS

M = λ1ψLHB1 R + λ2ψL ˜

HT 1

R + λ3ψL ˜

HT 2

R + λ4T 2 LT 1 R + λ5T 2 LT 2 R + h.c.

in this limit

MT ∼ λ5 , mt ∼ λ2v/ √ 2 , sL ∼ λ3v/MT

➡ if and is kept fixed,

and the singlet does not decouple! MT → ∞ sL λ3 → ∞

∆T ∼ TSM s2

L

• rs2

L − 2 + 2 log r

• → 0 ,

∆S ∼ − Nc 18π s2

L (5 − 2 log r) → 0 .

λ5 λ4

and

λ4, λ5 λ2v p 2 , λ3v p 2

➡ in the decoupling limit ( constant)

λ3

r = (MT /mt)2

In the singlet model, the strongest constraints come from the oblique parameters

CONSTRAINTS

mixing with the singlet reduces the coupling of the top-like quark to the Higgs and yields a coupling to the Higgs also for the heavy top partner the Higgs production cross section is suppressed with respect to the Standard Model

HIGGS PRODUCTION

Ytt = c2

L

mt v , YT T = s2

L

MT v YT t = sLcL mt v , YtT = sLcL MT v

σ(s)

gg→H

σSM

gg→H

≈ 1 − 7 15 m2

H

4m2

t

s2

L

✓ 1 − m2

t

M 2

T

◆ 1

decoupling

potentially large effect, but electroweak observables require a small mixing angle  at most some few % effect

HIGGS PRODUCTION

potentially large effect, but electroweak observables require a small mixing angle  at most some few % effect

HIGGS PRODUCTION

300 400 500 600 700 800 900 1000

MHH (GeV)

0.005 0.01 0.015 0.02

dσ/dMHH (fb/GeV)

SM, Exact SM, LET Singlet Top Partner, Exact Singlet Top Partner, LET

pp→HH, √S=8 TeV

mH=125 GeV, MT=1 TeV, cL=0.987

the top partner also affects loop mediated decays

• nly small mixing allowed  below-% effects

HIGGS DECAYS

H γ γ

assume no mixing with the Standard Model quarks, four additional heavy quarks, (charge 2/3), (charge -1/3), in the SU(2)L representations

MIRROR QUARKS

T 1,2 B1,2

as Standard Model families left  right

} }

ψ1

L =

✓ T 1

L

B1

L

◆ , T 1

R , B1 R ;

ψ2

R =

✓ T 2

R

B2

R

◆ , T 2

L , B2 L .

t, b

+λEψ

1 Lψ2 R + λF T 1 RT 2 L + λGB 1 RB2 L + h.c.

−LM = λAψ

1 LΦB1 R + λBψ 1 L ˜

ΦT 1

R + λCψ 2 RΦB2 L + λDψ 2 R ˜

ΦT 2

L

mass terms:

MIRROR QUARKS

MU = λB v

√ 2

λE λF λD v

√ 2

! MD = λA v

√ 2

λE λG λC v

√ 2

!

T

1 L

T

2 L

B

2 L

B

1 L

T 2

R

T 1

R

B1

R

B2

R

the mass eigenstates are obtained though unitary rotations  need four rotation angles for simplicity assume

T1, T2; B1, B2

MT1 = MB1 = M , MT2 = MB2 = M(1 + δ)

➡ six parameters, ➡ one condition,

MU,12 = MD,12 M, δ, θt

±, θb ± (θq L = θq L ± θq R) .

are large deviations from the Standard Model double Higgs rate compatible with

✦ electroweak bounds ✦ the measured single Higgs production cross section

?

HIGGS PRODUCTION

e.g., can we have a 15% or larger enhancement in the double Higgs amplitude (from the box contributions) while keeping single Higgs within 10% from the Standard Model?

HIGGS PRODUCTION

Fix mass splitting between the two quark mirror families fractional difference from the Standard Model single Higgs amplitude

δ

∆ Agg→H ≡ ASM

gg→H (1 + ∆)

➡ ➡

(2 + δ) sin θt

− + δ sin θt + = (2 + δ) sin θb − + δ sin θb +

sin θb

− =

1 2 + δ ⇢ (4 − ∆)(1 + δ) (2 + δ) sin θt

− − δ sin θb +

− δ sin θb

+

HIGGS PRODUCTION

• 1
• 0.5

0.5 1 θ+

b/π

• 0.6
• 0.4
• 0.2

0.2 0.4 0.6 θ-

t/π

| Δ | < 0.1 Δbox > 0.15

MT1 = MB1 = M, MT2 = MB2 = M(1+δ), 0 < δ < 1

➡ Fix θt

− = π

2

HIGGS PRODUCTION

Text

• 1
• 0.5

0.5 1 θ+

b/π

0.9 0.95 1 1.05 1.1 1.15 1+Δbox

δ = 1 δ = 0.75 δ = 0.5 δ = 0.25

Δ = +0.1 Δ = -0.1

• 1
• 0.5

0.5 1 θ+

b/π

1 1.05 1.1 1+Δbox

δ = 0.25 δ = 0.5 δ = 0.75 δ = 1

Δ = 0

∆box ' ∆ ⇥ 1 δ2 cos2 θb

+ + O(δ3)

⇤ + δ4 cos4 θb

+

1 2 δ(1 sin θb

+)

the mirror quarks also contribute to the self energies

• f the electroweak gauge bosons  bounds from the

S, T, U parameters

FORGOT ANYTHING?

• 1
• 0.5

0.5 1

sin θ+

b

1 2

δ

• 1
• 0.5

0.5 1

sin θ+

b

1 2

δ

• 1
• 0.5

sin θ+

• 0.4
• 0.2

δ

95% CL regions allowed from S,T,U fit

electroweak and single Higgs constraints do not allow for significant changes in double Higgs production

✦ the largest enhancement is below 20% (for ) ✦ small effects on the differential distributions

DOUBLE HIGGS PRODUCTION

the bounds from electroweak observables allow for large suppressions (up to -90%) or enhancements (up to +10%) in ! but.. for a single Higgs rate within 10% the Standard Model value these deviations are reduced to 10% !

HIGGS DECAYS

effective Lagrangian for gluon-Higgs interactions (up to dim. 6 operators)

GLUON-HIGGS OPERATORS

✦ renormalizable ✦ dimension 6 ✦ not present in the SM

➡

GLUON-HIGGS OPERATORS

contribute differently to Higgs single and pair production,

O1 ∝Ga

µνGa,µν

✓H v + H2 2v2 ◆ O2 ∝Ga

µνGa,µν

✓H v − H2 2v2 ◆

➡ cH ≡ c1 + c2 , cHH ≡ c1 − c2

in the singlet model  as Standard Model

c1 = 0

in the mirror fermion model

GLUON-HIGGS OPERATORS

βt,b = 0

require single Higgs close to Standard Model

cH → cSM

H (1 + ∆) = 1 + ∆



cHH → 2c1 − (1 + ∆) ct

2 = 1 +

2 (1 − βt)2 cb

2 =

2 (1 − βb)2

➡ need large   either massless or

infinitely heavy quarks! βq ' 1

c1

ct,b

1

= −2βt,b (1 − βt,b)2 cSM

1

= 0

Dirac couplings Yukawa couplings

mass entirely from EWSB

βq ∼

vector singlet its mixing with the top quark strongly constrained by S, T, U  forced almost to decouple decoupling: would yield reduced Higgs production rates electroweak bounds allow only for a few % effect in single Higgs production, and at most a 15% effect in double Higgs enhancement in the branching ratio below % level

➡ same phenomenology as the Standard Model

CONCLUSIONS

H → γγ

MT → ∞, sL ∼ vM −1

T

mirror fermions electroweak bounds allow for large enhancement/ suppression in Higgs rates require single Higgs rate to be close to the measured one

➡ double Higgs cross section and distributions also

become close (within 20%) to the Standard Model ones

➡ the Higgs branching ratio into photons is within

10% the Standard Model prediction

CONCLUSIONS

connection to the effective gluon-Higgs operators singlet model: only the Standard Model like operator is induced mirror fermion model

➡ large deviations in Higgs pair production require

large

➡ only possible for massless or infinitely heavy

quarks!

CONCLUSIONS

O2 c1