Higgs Boson Physics, Part III

Laura Reina

TASI 2004, Boulder

Outline of Part III

• Searching for a Higgs boson: present and future.

• Higgs boson physics at the Tevatron, Run II.

−→ Main production modes.−→ Exclusion/discovery reach for a SM/MSSM Higgs boson.

• Higgs boson physics at the Large Hadron Collider (LHC).

−→ Main production modes.−→ Discovery reach for a SM/MSSM Higgs boson.−→ Measurements of the Higgs boson mass, width, spin.−→ Measurements of Higgs boson couplings.

• Higgs boson physics at a high energy Linear Collider (LC).

−→ Production reach for a SM/MSSM Higgs boson.−→ Precision measurements of most Higgs boson properties.

Some References for Part III

• Theory and Phenomenology of the Higgs boson(s):. Higgs Boson Theory and Phenomenology,

M. Carena and H.E. Haber, hep-ph/0208209

• Specific studies and reports:. CMS Collaboration, CERN/LHCC/94-38,1994. ATLAS Collaboration, CERN/LHCC/99-15,1999. Report of the Tevatron Higgs working group, hep-ph/0010338.. Proceedings of the Les Houches Workshop on Physics at TeV

Colliders, 2001.. Results of the Tevatron Higgs sensitivity study, October 2003.. Les Houches workshop on Physics at TeV Colliders: report of the

Higgs working group, hep-ph/0406152.. TESLA technical design report, Part III, hep-ph/0106315.. Linear Collider Physics Resourche Book, Part II, hep-ex/0106056.

Searching for the Higgs boson: present and future

. A light Higgs boson, in the 110-180 GeV range, could be discovered

during Run II of the Tevatron (Fermilab), with√

s=1.96 TeV.

. The Large Hadron Collider (CERN), with√

s=14 TeV, will cover

the entire Higgs boson mass range up to 1 Tev, and start measuring

mass, couplings, and width of the discovered particle.

. A high energy LC (?), with√

s ≥ 500 GeV, will unambiguously

identify the nature of any discovered new particle, via precision

measurements of its mass, spin, couplings, and width.

The basic picture of a pp̄, pp → X high energy process . . .

X

f (x )

fj(x )2

p

p,p

i 1i

j

σij

where the short and long distance part of the QCD interactions can be

factorized and the cross section for pp, pp̄ → X can be calculated as:

σ(pp, pp̄ → X) =∑

ij

∫

dx1dx2fip(x1)fj

p,p̄(x2)σ̂(ij → X)

−→ ij → quarks or gluons (partons)−→ f

pi (x), f

p,p̄i (x): Parton Distributions Functions: probability densities

(probability of finding parton i in p or p̄ with a fraction x of the original

hadron momentum)−→ σ̂(ij → X): partonic cross section

pp̄, pp colliders: SM Higgs production modes

gg → H

g

g

t , XH

qq → qqH

q

q

W,Z

W,Z

q′,q

q’,q

H

qq → WH, ZH

q

q

Z,W

Z,W

H

qq̄, gg → tt̄H, bb̄H

q

q

t,b

t,b

H

g

g

g

t,b

t,b

H

g

g

g

t,b

t,b

H

g

g

t,b

t,b

H

Searching for a SM Higgs boson at the Tevatron

σ(pp_→hSM+X) [pb]

√s = 2 TeV

Mt = 175 GeV

CTEQ4Mgg→hSM

qq→hSMqqqq

_’→hSMW

qq_→hSMZgg,qq

_→hSMtt

_

gg,qq_→hSMbb

_

bb_→hSM

Mh [GeV]SM

10-4

10-3

10-2

10-1

1

10

10 2

80 100 120 140 160 180 200

Mainly in:

• Below 130-140 GeV

qq̄ → V H, H → bb̄• Above 130-140 GeV

qq̄ → V H, H → WW

with V = Z, W

But also:

• gg → H (above 130 GeV)• qq̄ → tt̄H (H → bb̄, WW )

Too low statistics to measure Higgs

couplings.

Reach of the Tevatron, Run II, for a SM Higgs boson

Improved studies suggest that less luminosity is neededboth for exclusion and discovery.

Searching for an MSSM Higgs boson at the Tevatron

We expect that:

• AV V couplings are absent

• couplings can be enhanced/suppressed

. MA À MZ (−→ decoupling limit):

−→ h0 −→ HSM , while

−→ MA ' MH and g(A,H)bb̄ À gHSM bb̄ , gHV V ¿ gHSM V V .

. MA ≤ MZ and tanβ À 1:

−→ gHV V ' gHSM V V , while

−→ MA ' Mh and g(A,h)bb̄ À gHSM bb̄ , ghV V ¿ gHSM V V .

We could also have:

• Higgs bosons decaying into supersymmetric particles.

• Higgs bosons produced in the decay of supersymmetric particles.

We will consider only:

. SM-like production modes (see previous section)

. the associated production modes:

p

p,p

Z

h0,H0

A0

p

p,p

Z,γ

H+

H-

Neutral Higgs boson production cross sections at the Tevatron

σ(pp_→h/H+X) [pb]

√s = 2 TeV

Mt = 175 GeV

CTEQ4

Mh/H [GeV]

tgβ = 3

gg→H

Hbb_

Htt_

Hqq

HZ

HW

gg→h

hbb_

htt_

hZhW

hqq

h H❍ ❍10

-4

10-3

10-2

10-1

1

10

10 2

80 100 120 140 160 180 200

σ(pp_→h/H+X) [pb]

√s = 2 TeV

Mt = 175 GeV

CTEQ4

Mh/H [GeV]

tgβ = 30

gg→H

Hbb_

Htt_

HZ

HW

←Hqq

bb_→H

bb_→h

gg→h

hbb_

htt_hZ

hW

hqqh H❍ ❍

10-4

10-3

10-2

10-1

1

10

10 2

10 3

10 4

80 100 120 140 160 180 200

σ(pp_→A+X) [pb]

√s = 2 TeV

Mt = 175 GeV

CTEQ4

tgβ = 3gg→A

gg,qq_→Abb

_

MA [GeV]

10-4

10-3

10-2

10-1

1

10

80 100 120 140 160 180 200

σ(pp_→A+X) [pb]

√s = 2 TeV

Mt = 175 GeV

CTEQ4

tgβ = 30gg→A

gg,qq_→Abb

_

bb_→A

MA [GeV]

10-1

1

10

10 2

80 100 120 140 160 180 200

0 10 20 30 40 50 60

tan β

0.00

0.10

0.20

0.30

0.40

0.50

0.60 BR0(t−> H

+ b)

BRQCD

(t−> H+ b)

BRMSSM

(t−> H+ b)

H± production at the Tevatron

. MH± < mt − mb :

−→ pp̄ → tt̄ + t → bH+ (t̄ → b̄H−)

−→ pp̄ → t̄bH+, tb̄H−

. MH± > mt − mb :

−→ pp̄ → t̄bH+, tb̄H−

−→ pp̄ → W±H∓

−→ pp̄ → H+H−

Reach of the Tevatron, Run II, in the MSSM parameter space

Using:

−→ pp̄ → V φ (φ = h0, H0)

−→ pp̄ → bb̄φ (φ = h0, H0, A0)

Searching for a SM Higgs boson at the LHC

σ(pp→H+X) [pb]

√s = 14 TeV

Mt = 175 GeV

CTEQ4Mgg→H

qq→Hqqqq

_’→HW

qq_→HZ

gg,qq_→Htt

_

gg,qq_→Hbb

_

MH [GeV]

0 200 400 600 800 100010

-4

10-3

10-2

10-1

1

10

10 2

Below 130-140 GeV:

• gg → H , H → γγ, W+W−, ZZ

• qq → qqH , H → γγ, W+W−, ZZ, τ+τ−

• qq̄, gg → tt̄H , H → bb̄, τ+τ−

BR(H)

bb_

τ+τ−

cc_

gg

WW

ZZ

tt-

γγ Zγ

MH [GeV]

50 100 200 500 100010

-3

10-2

10-1

1

Above 130-140 GeV:

• gg → H , H → W+W−, ZZ

• qq → qqH , H → γγ, W+W−, ZZ

• qq̄, gg → tt̄H , H → W+W−

Discovery reach of the LHC for a SM Higgs boson

1

10

10 2

100 120 140 160 180 200

mH (GeV)

Sig

nal s

igni

fica

nce

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

1

10

10 2

102

103

mH (GeV)

Sig

nal s

igni

fica

nce

H → γ γ + WH, ttH (H → γ γ ) ttH (H → bb) H → ZZ(*) → 4 l

H → ZZ → llνν H → WW → lνjj

H → WW(*) → lνlν

Total significance

5 σ

∫ L dt = 100 fb-1

(no K-factors)

ATLAS

Low luminosity High luminosity

Mass, Width, Spin and more

• Color and charge are given by the measurement of a given

(production+decay) channel.

• The Higgs boson mass will be measured with 0.1% accuracy in

H → ZZ∗ → 4l±, complemented by H → γγ in the low mass region.

Above MH ' 400 GeV precision deteriorates to ' 1% (lower rates).

• The Higgs boson width can be measured in H → ZZ∗ → 4l± above

MH ' 200 GeV. The best accuracy of ' 5% is reached for MH ' 400 GeV.

Below MH ' 200 GeV −→ see later.

• The Higgs boson spin could be measured through angular correlations

between fermions in H → V V → 4f , but this will be impaired by lack of

statistics.

The LHC can also measure most SM Higgs couplings at 10-30%!

gg→ HWBFttHWH

● ττ ● bb● ZZ ● WW● γγ

MH (GeV)

∆σH/σ

H (

%)

0

5

10

15

20

25

30

35

40

110 120 130 140 150 160 170 180

Consider all accessible channels:

• Below 130-140 GeV

gg → H , H → γγ, WW, ZZ

qq → qqH , H → γγ, WW, ZZ, ττ

qq̄, gg → tt̄H , H → bb̄, ττ

• Above 130-140 GeV

gg → H , H → WW, ZZ

qq → qqH , H → γγ, WW, ZZ

qq̄, gg → tt̄H , H → WW

Observing a given production+decay (p+d) channel gives a relation:

(σp(H)Br(H → dd))exp =σth

p (H)

Γthp

ΓdΓp

Γ

(in the narrow Higgs approximation).

Associate to each channel (σp(H) × Br(H → dd))

Z(p)d =

ΓpΓd

Γ

{

Γp ' g2Hpp = y2

p → production

Γd ' g2Hdd = y2

d → decay

From LHC measurements, given the current simulated accuracies:

• Determine in a model independent way ratios of couplings at the

10 − 20% level, for example:

yb

yτ

←−Γb

Γτ

=Z

(t)b

Z(t)τ

yt

yg

←−Γt

Γg

=Z

(t)τ Z

(w)γ

Z(w)τ Z

(g)γ

• Determine individual couplings at the 10-30% level

(under the assumption: Γ = Γb + Γτ + Γw + Γz + Γg + Γγ)

Accuracies on Couplings and Width of a Higgs boson withMH <140 GeV

0

10

20

30

40

50

60

0

5

10

15

20

25

30

35

40

0

10

20

30

40

50

60

110 120 130 140

- - Γtot ● Γt ● Γb ● Γτ

● ΓW,ΓZ ● Γγ ● Γg

ΓZ/ΓW=zSM, no syst

Γb

Γτ

Γtot

Γg

ΓW,Z

Γt

Γγ

expe

cted

acc

urac

y (

%)

ΓZ/ΓW=zSM, Γb/Γτ=ySM,no syst

ΓZ/ΓW=zSM, syst

Γb

Γτ

Γtot

Γg

ΓW,Z

Γt

Γγ

ΓZ/ΓW=zSM, Γb/Γτ=ySM, syst

MH (GeV)

0

5

10

15

20

25

30

35

40

110 120 130 140

systematics:

theoretical error on

gg → H −→ 20%

qq → qqH −→ 5%

pp → tt̄H −→ 10%

Plus assumptions on ΓZ/ΓW

(and Γτ/Γb)

Toward a more model independent determination of Higgscouplings and width

[GeV]Hm110 120 130 140 150 160 170 180 190

(H,X

)2

g(H

,X)

2 g∆

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1(H,Z)2g

(H,W)2g

)τ(H,2g

(H,b)2g

(H,t)2g

HΓ

without Syst. uncertainty

2 Experiments-1

L dt=2*30 fb∫

[GeV]Hm110 120 130 140 150 160 170 180 190

(H,X

)2

g(H

,X)

2 g∆

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1(H,Z)2g

(H,W)2g

)τ(H,2g

(H,b)2g

(H,t)2g

HΓ

without Syst. uncertainty

2 Experiments-1

L dt=2*300 fb∫-1WBF: 2*100 fb

Global χ2 fit

assuming

−→ g2(H, V ) < g2(H, V, SM) + 5% (V = W, Z)

−→ new particles in loop production/decay modes

−→ unobservable decay modes

MSSM Higgs boson production cross sections at the LHC

10-3

10-2

10-1

1

10

10 2

10 3

10 4

102

gg→H (SM)

gg→HHbb

–

Htt–

Hqq

HZ HW

tan β = 3

Maximal mixing

➙ H

➙

h

mh/H (GeV)

Cro

ss-s

ectio

n (p

b)

10-3

10-2

10-1

1

10

10 2

10 3

10 4

102

gg→H (SM)

gg→AAbb

–

Att–

tan β = 3

Maximal mixing

mA (GeV)

Cro

ss-s

ectio

n (p

b)

10-3

10-2

10-1

1

10

10 2

10 3

10 4

102

gg→H (SM)

gg→H

Hbb–

Htt–

Hqq

HZ HW

tan β = 30

Maximal mixing

➙ H

➙

h

mh/H (GeV)

Cro

ss-s

ectio

n (p

b)

10-3

10-2

10-1

1

10

10 2

10 3

10 4

102

gg→H (SM)

gg→A

Abb–

Att–

tan β = 30

Maximal mixing

mA (GeV)

Cro

ss-s

ectio

n (p

b)

H± production at the LHC

(see Tevatron section for more details on production modes)

Reach of the LHC in the MSSM parameter space

Low luminosity, CMS only High luminosity, ATLAS+CMS

e+e− colliders: SM Higgs production modes

e-

e+

Z,W

Z,W

H

e-

e+

W,Z

W,Z

νe,e-

νe,e+

H

e+

e-

t,b

t,b

H

γ,Z

e+

e-

t,b

t,b

Hγ,Z

e+

e-

t,b

t,b

H

γ,Z

and additional MSSM modes

e-

e+

Z

h0,H0

A0

e-

e+

Z,γ

H+

H-

The Linear Collider: precision Higgs physics

Production cross sections for a SM Higgs boson:

�� �

� � �� � � � � � � � � � � � � � � � � � � � �

� � � � � � � � � �� � �

� � � � � � � � � � � � � � ! "

# $# %& %

σ(e+e− → tt_H) [fb]

√s = 800 GeV

√s = 500 GeV

MH [GeV]

0.5

1

2

3

4

5

100 110 120 130 140 150 160 170 180

Production cross sections for an MSSM Higgs boson:

'' (

' ( (' ( ( ' ) * ' * ( ' + * ) ( ( ) ) * ) * (

, - . / .0 1 2 3 4 5 67 8 9

: ; < = > ? @ A BC DC E

2 F 2 F2 G 2 G

4 F

4 G4 F

4 G

'' (

' ( (' ( ( ' * ( ) ( ( ) * ( H ( ( H * ( I ( (

, - . / .0 1 4 G 5 67 8 9

, - . / .0 1 4 / 4 0 5 67 8 9

: ; < J ? ? @ A B

C K

L M N O < =

L M N O < = ?

Program:

One or more Higgs bosons will be observed over the entire mass spectrum.

A high energy e+e− collider will then have the unique possibility of:

• Measure σ(e+e− → ZH) at the 2% level: extract Br(H → xx) in model

independent way!

• Measure MH from the recoiling ff̄ mass in ZH → Hff̄ . Accuracies of

the order of 50-80 MeV can be obtained.

•

s (GeV)

cros

s se

ctio

n (f

b)

J=0

J=1

J=2

0

5

10

15

210 220 230 240 250

spin measured by:

. onset slope of the e+e− → ZH

. correlations in e+e− → ZH → 4f , . . .

. phase space distributions in e+e− → tt̄H

• Measure ΓH below MH ' 200 Gev combining Br(H → W+W−) (from

e+e− → ZH) and gHWW (from e+e− → Hνν̄), with a ' 6% accuracy.

Ex.: SM Higgs boson,√

s=120 GeV

Coupling: Hbb̄ Hτ+τ− Hcc̄ HWW HZZ Htt̄ HHH

(MH =120 GeV) 2.2% 3.3% 3.7% 1.2% 1.2% 25% 17%

(MH =140 GeV) 2.2% 4.8% 10% 2.0% 1.3% 23%

Theory 1.4% 2.3% 23% 2.3% 2.3% 5%

Difficult measurements:

500 600 700 800 900 1000√s (GeV)

0

1

2

3

4

σ (f

b)

e+e

- -> tth

Mh=110 GeVMh=130 GeV

Top quark Yukawa coupling:

Optimal scale√

s ' 700 − 800 GeV:

−→√

s=800 GeV: δgtth

gtth' 5.5%

−→√

s=500 GeV: δgtth

gtth' 25%

−→ Can the LHC complement it?

100 120 140 160 1800

0.2

0.1

0.3

MH[GeV]

SM Double Higgs-strahlung: e+ e- → ZHH

σ [fb]

√s = 800 GeV

√s = 500 GeV

●

●

●

Higgs boson self-coupling

−→ need to wait for CLIC?

Optimal to distinguish HSM from h0

gW/gW(SM)

gb/g

b(S

M)

MSSM prediction:200 GeV < mA < 400 GeV

400 GeV < mA < 600 GeV

600 GeV < mA < 800 GeV

800 GeV < mA < 1000 GeV

LC 95% CL (w/o fusion)

LC 1σ (w/o fusion)

LC 95% CL (with fusion)

LC 1σ (with fusion)

mH = 120 GeVc)

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

gW/gW(SM)

gb/g

b(S

M)

MSSM prediction:200 GeV < mA < 400 GeV

400 GeV < mA < 600 GeV

600 GeV < mA < 800 GeV

800 GeV < mA < 1000 GeV

LC 95% CL (w/o fusion)

LC 1σ (w/o fusion)

LC 95% CL (with fusion)

LC 1σ (with fusion)

mH = 120 GeVc)

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

gtau/gtau(SM)

gb/g

b(S

M)

mH = 120 GeV

200 GeV < mA < 400 GeV

400 GeV < mA < 600 GeV

600 GeV < mA < 800 GeV

800 GeV < mA < 1000 GeV

LC 1σLC 95% CL

MSSM prediction

d)

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2

gtau/gtau(SM)

gb/g

b(S

M)

mH = 120 GeV

200 GeV < mA < 400 GeV

400 GeV < mA < 600 GeV

600 GeV < mA < 800 GeV

800 GeV < mA < 1000 GeV

LC 1σLC 95% CL

MSSM prediction

d)

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2