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