Higgs decays to γγ and Zγ in
models with Higgs extensions
Kei Yagyu (National Central U.)
Collaboration with
Cheng-Wei Chiang (National Central U.)
arXiv: 1207.1065 [hep-ph]
Academia Sinica, September 14th
Plan of Talk
• Introduction
- SM Higgs sector
- Current states of the Higgs search at LHC
• Extended Higgs sectors
• Higgs decays into γγ and Zγ
• Summary
Higgs, 希格斯, ヒッグス
• God particle?
- Trigger the electroweak
symmetry breaking
- The Higgs VEV: Unique mass scale
(Excepted for ΛQCD)
- Origin of Mass: Gauge bosons → Higgs mechanism
Quarks & Leptons → Yukawa interaction
The “God” really has been discovered at the LHC ??
Higgs sector in the SM
V (φ)
Higgs potential
Φ: isospin SU(2) scalar doublet
F=
f+
f0
Higgs VEV
φ0
φ+
SU(2)L×U(1)Y → U(1)EM
Physical state: Only one neutral component h
Origin of Mass
Gauge boson mass
V
V
g2
<F>
<F>
mV2 = g2v2
Fermion mass
f
y
<F>
Higgs mass
F
F
f
mf = y v
λ
<F>
<F>
mh2 = λv2
All the masses of particles are given by the Higgs VEV.
Higgs sector in the SM
V (φ)
Higgs potential
Φ: isospin SU(2) scalar doublet
F=
f+
f0
Higgs VEV
φ0
φ+
SU(2)L×U(1)Y → U(1)EM
Physical state: Only one neutral component h
Higgs Interaction
Gauge interaction
V
V
g2
F
F
∝ mV 2 / v 2
Yukawa interaction
f
y
F
Self interaction
F
F
f
∝ mf / v
λ
F
F
∝ mh2/v2
All the Higgs interactions are proportional to the mass
Higgs search at collider experiments
e+e-
X
(LEP, ILC),
pp (Tevatron),
pp (LHC),…
Beam
・
・
・
Higgs boson
Production
Decay
Detector
Depends on
Collision particle,
Center of mass energy,
…
Theory
(Model)
Theory
(Model)
Detector
performance,
…
We should know the production and decay property of the Higgs boson.
Branching fraction
f
h
f
W+, Z
h
W-, Z
γ, g
h
γ, g
‣ bb mode: Large branching ratio, but huge background
‣ γγ, ZZ(*) → 4 lepton mode: Tiny branching ratio, but small background
Higgs boson production at the LHC
Gluon Fusion ~ 10 pb
W/Z association
V. Sharma, talk at Moriond (2011)
Vector Boson Fusion ~ 1 pb
Top quark association
Current states of the Higgs search at the LHC
‣ The Higgs-like particle has been found at around 126 GeV
at the LHC with 5σ.
h → γγ
h → ZZ* → 4 lepton
Historic Milestone but only the Beginning.
R. Heuer, July 4th, CERN
Current states of the Higgs search at the LHC
Signal strength (σobs/σSM) in each mode
1207.7214 [hep-ex], CMS
1207.7235 [hep-ex], ATLAS
Current states of the Higgs search at the LHC
Signal strength (σobs/σSM) in each mode
1207.7214 [hep-ex], CMS
1207.7235 [hep-ex], ATLAS
H → ZZ and H→ WW modes are good agreement to the SM prediction.
Current states of the Higgs search at the LHC
Signal strength (σobs/σSM) in each mode
1207.7214 [hep-ex], CMS
1207.7235 [hep-ex], ATLAS
Obs. H → γγ signal seems to be large compared to the SM prediction.
Current states of the Higgs search at the LHC
Signal strength (σobs/σSM) in each mode
1207.7214 [hep-ex], CMS
1207.7235 [hep-ex], ATLAS
H → ττ and H → bb modes have large uncertainty.
At CMS, H → ττ mode did not seem to be discovered yet.
SM-like Higgs boson?
• At present, observed new resonance at 126 GeV looks like the
SM-like Higgs boson.
(-Consistent with the precision measurements at LEP,
- Observed from expected events γγ and ZZ → H is spin 0 or 2)
• Large deviation from the SM in H→γγ mode
• No observation from H→ττ mode
We need to collect more data in order to clarify the property
of the new particle w/126 GeV.
Still there are possibilities to consider non-minimal Higgs sectors!
Extended Higgs sector
Explanation by extended Higgs sectors
• Tiny neutrino masses
- The type II seesaw model
- Radiative seesaw models
(e.g. Zee model)
• Dark matter
- Higgs sector with an unbroken discrete symmetry
• Baryon asymmetry of the Universe
- Electroweak baryogenesis
Introduced extended Higgs sectors
SU(2) doublet Higgs + Singlets, Doublets and Triplets, …
Beyond the SM
Extended Higgs sectors
Determine
What is the true Higgs sector?
There are hints to determine the structure of the Higgs sector.
1. Electroweak rho parameter
+0.0017
ρexp = 1.0008 -0.0007
Additional Doublets or Singlets
Additional Triplets or Higher isospin reps.
→ ρtree = 1
→ In general, ρtree ≠ 1
Small triplet VEV or Custodial sym.
(Georgi-Machacek model)
2. Flavor Changing Neutral Current (FCNC)
Tree level FCNC process should be suppressed.
Extension of Multi-doublets → In general, there appears the FCNC at the tree level.
A discrete Z2 symmetry is often imposed to avoid the tree level FCNC.
Glashow, Weinberg
Testing an extended Higgs sector at colliders
• Direct way：Discovery of extra Higgs bosons
Ex. Charged Higgs boson, CP-odd Higgs boson, …
• Indirect way:
Precise measurement for the Higgs couplings
Ex. hhh, hff, hVV
Testing an extended Higgs sector at colliders
• Direct way：Discovery of extra Higgs bosons
Ex. Charged Higgs boson, CP-odd Higgs boson, …
• Indirect way:
Precise measurement for the Higgs couplings
Ex. hhh, hff, hVV
We discuss the 2 Higgs doublet model and
the Higgs triplet model as important examples.
Two Important examples
• 2 Higgs Doublet Model (2HDM)
- Many new physics models deduce the 2HDM.
ex. MSSM, Dynamical Sym. breaking models,
Radiative seesaw models, and so on.
- Source of the CP-violation
• Higgs Triplet Model (HTM)
Cheng, Li (1980);
Schechter, Valle, (1980);
Magg, Wetterich, (1980);
Mohapatra, Senjanovic, (1981).
- Tiny neutrino masses can be generated via
the type-II seesaw mechanism.
Higgs potential in the 2HDM
The Higgs potential under the softly broken Z2 sym. (Φ1 → + Φ1, Φ2 → -Φ2)
Physical scalar states: 8-3 = 5
CP-even Higgs
Goldstone bosons
Charged Higgs
Mass formulae (sin(β-α) ~1 )
SM-like Higgs boson
Extra Higgs bosons
Tanβ = v2/v1
CP-odd Higgs
Four types of the Yukawa interaction
Imposing Z2 symmetry → Only one of the two doublet couples to each fermion.
Barger, Hewett, Phillips PRD 41 (1990)
W－
Grossman NPB 426 (1994)
Type-I
Φ２
u
d
e
Type-X
Φ２ Φ１
u
e
d
Type-II (MSSM)
b
Φ２ Φ１
u
d
e
t
Bs → sγ
H－
γ
s
γ
b
t
s
Aoki, Kanemura, Tsumura, Yagyu, PRD 80, 2009
Type-Y
Φ２
u
e
d Φ１
In the Type-I and Type-X 2HDM, a light charged Higgs boson can be allowed.
CP-odd Higgs (A) decay in the case with
sin(β-α) = 1, mA = mH =150 GeV
Type II (MSSM-like)
Type X
(μ+)
(μ-)
Kanemura, Tsumura, Yokoya, PRD 85 (2012)
Higgs potential in the HTM
The Higgs potential
Physical scalar states: 10 -3 = 7
Doubly-charged Higgs
CP-even Higgs
Mass formulae (vΔ/vφ << 1 )
Triplet-like
SM-like
NG bosons
Singly-charged Higgs
CP-odd Higgs
Case I (λ5 >0)
Mass2
Case II (λ5<0)
Mass2
A, H
H++
H+
H+
H++
A, H
Branching ratio of H++
Without mass splitting
With mass splitting
(mH++ - mH+ = 10 GeV)
Phenomenology with the mass splitting is drastically different from that
without the mass splitting
Mass reconstruction
140 GeV
H+
130 GeV
119 GeV
114 GeV
H, A
h
Aoki, Kanemura, KY, PRD85(2012)
qq’ → H++H- → (l+l+ννbb)(jjbb)
H++
qq’ → H+H → (l+νbb)(bb)
vΔ = 10-2 GeV
qq → HA → (bb)(bb)
MT, Minv
MT
MT
Signal only
mH++
130 fb
42 fb
33 fb
12 fb
8.0 fb (14 TeV)
2.8 fb (7 TeV)
mH+
mH, mA
All the masses of the Δ-like scalar bosons may be reconstructed.
Higgs decays into the γγ and Zγ
Testing an extended Higgs sector at colliders
• Direct way：Discovery of extra Higgs bosons
Ex. Charged Higgs boson, CP-odd Higgs boson, …
• Indirect way:
Precise measurement for the Higgs couplings
Ex. hhh, hff, hVV
We discuss Higgs decays into the diphoton (hγγ) and
the Z + photon (hZγ).
Higgs to the diphoton channel
CMS, ICHEP
ATLAS, ICHEP
The signal strength σOBS/σSM exceeds 1 at the both experiments:
1.56± 0.43 (CMS), 1.9±0.5 (ATLAS).
‣ If this excess is really established,
it must be explained by effects of new physics beyond the SM!
We focus on new physics effects to the H → γγ and H → Zγ modes.
h → γγ and h → Zγ decays in the SM
‣The hγγ and hγZ verteces are induced at the 1-loop level.
Top quark loop contribution
(Z)
‣Decay rate
W boson loop contribution
(Z)
Ellis, Gaillard, Nanopoulos, (1976) ;
Ioffe, Khoze, (1978);
Shifman, Vainshtein, Voloshin, Zakharov, (1979)
Cahn, Chanowitz, Fleishon, (1979);
Bergstrom, Hulth, (1985)
h → γγ and h → Zγ decays in the SM
‣The hγγ and hγZ verteces are induced at the 1-loop level.
Top quark loop contribution
W boson loop contribution
(Z)
(Z)
‣Decay rate
Ellis, Gaillard, Nanopoulos, (1976) ;
Ioffe, Khoze, (1978);
Shifman, Vainshtein, Voloshin, Zakharov, (1979)
Cahn, Chanowitz, Fleishon, (1979);
Bergstrom, Hulth, (1985)
‣Input parameters: mh = 126 GeV, mt = 173 GeV
Mode
Top-loop
W-loop
Decay rate Branching
h → γγ
-1.84
8.38
10.7 keV
0.28 %
h → Zγ
-0.643
12.1
7.12 keV
0.18 %
W and top loop effects
are destructive
with each other.
h → γγ and h → Zγ decays in the SM
‣The hγγ and hγZ verteces are induced at the 1-loop level.
Top quark loop contribution
W boson loop contribution
(Z)
(Z)
‣Decay rate
Ellis, Gaillard, Nanopoulos, (1976) ;
Ioffe, Khoze, (1978);
Shifman, Vainshtein, Voloshin, Zakharov, (1979)
Cahn, Chanowitz, Fleishon, (1979);
Bergstrom, Hulth, (1985)
‣Input parameters: mh = 126 GeV, mt = 173 GeV
Mode
Top-loop
W-loop
Decay rate Branching
h → γγ
-1.84
8.38
10.7 keV
0.28 %
h → Zγ
-0.643
12.1
7.12 keV
0.18 %
W and top loop effects
are destructive
with each other.
How these predictions are changed by new physics effects?
New physics effects to h→γγ(Z)
‣ Any charged new particle which couples to the Higgs boson
can contribute to the h→ γγ and h → Zγ processes.
(Z)
Spin 0
Ex. Charged Higgs boson,
Squark, Slepton…
(Z)
Spin 1/2
Ex. 4th generation fermion,
Chargino…
(Z)
Spin 1
Ex. W’ boson…
In this talk, we focus on modes with extended Higgs sector,
where new charged scalar bosons are introduced to the SM.
Previous works and our work
There are several papers where the
h→γγ mode is studied in an extended Higgs sector.
・ 2 Higgs doublet model
Posch 2011;
Arhrib, Benbrik, Gaur 2012;
Ferreira, Santos, Sher, Silva 2012
・ Higgs triplet model
Arhrib, Benbrik, Chabab, Moultakae, Rahilib 2012;
Kanemura, Yagyu 2012;
Akeroyd, Moretti 2012
・ Zee model (2HDM + charged singlet)
Kanemura, Kasai, Lin, Okada, Tseng, Yuan 2000
We study the h→γγ(Z) more comprehensive way in various extended Higgs sectors.
Classes of extended Higgs sectors
‣ 3 classes of extended Higgs sectors.
Class I : Models with one singly-charged scalar boson
SM
H±
Ex. 2HDM
Class II : Models with one singly-charged and
one doubly-charged scalar boson
SM
H±
Ex. Higgs triplet model,
Zee-Babu model
H±±
Class III : Models with two singly-charged scalar bosons
SM
H1±
H2±
Ex.: Radiative seesaw models
(Zee model,
Kauss-Nasri-Trodden model,
Aoki-Kanemura-Seto model)
List of models
‣ We consider Higgs sectors with additional
SU(2)L singlets (S), doubles (D) and triplets (T).
Class I
Singlet
Class II
Class III
(Y = 1)
(Y = 2)
Doublet (Y = 1/2)
Triplet
(Y = 0)
(Y = 1)
There are 13 models depending on the # of scalar fields.
SM-like Higgs boson
‣ We assume the SM-like Higgs boson (h):
-The Yukawa coupling (hff) and the gauge coupling (hVV)
is the same as those in the SM.
X
・
・
・
h
Production
Same as the SM
Decay
Only h→γγ and h→Zγ decay modes can be modified
significantly. The other decay rates are almost
the same as the SM.
Modified decay rate directly affects to the number of events.
Modified decay rates
‣ Decay rates are modified by new contributions from charged scalar bosons:
‣ The Higgs couplings with charged scalars (λSSh) and the
Z boson (gSSZ) can be defined as
Points
1. Decay rate of h→γγ is
enhanced when λSSh is negative.
suppressed when λSSh is positive.
2. Decay rate of h→ Zγ depends on the isospin (I3) of the scalar boson.
Measuring both h→γγ and h→Zγ would be a useful tool to determine the true Higgs sector.
Relevant terms in Class I and II
⊃
Φ : SM doublet
1, 2
⊃
: Extra scalar field
Relevant terms in Class III
⊃
=
M1 = M2 = M3
=M
≠
M1 = M2 = M3
=M
Mixing angle:
Results (Class I and Class II)
mH+ = mH++ = 200 GeV
ΔB (h → X) =
[Br(h → X)NP - Br(h → X)SM]/ Br(h → X)SM
Class I
Not allowed by the
vacuum stability bound.
Class II
Results (Class I and Class II)
mH+ = mH++ = 200 GeV
Class I
R = Br(h → Zγ)NP/ Br(h → γγ)NP
Not allowed by the
vacuum stability bound.
Class II
Results (Class III)
mH1+ = 200 GeV, mH2+ = 300 GeV,
M = 308 GeV
ΔB (h → X) =
[Br(h → X)NP - Br(h → X)SM]/ Br(h → X)SM
Results (Class III)
mH1+ = 200 GeV, mH2+ = 300 GeV,
M = 308 GeV
R = Br(h → Zγ)NP/ Br(h → γγ)NP
Summary
• To know the true Higgs sector → To determine physics beyond the SM.
1.
2.
Direct way : Discovery extra Higgs bosons
Decay of the extra Higgs is important to discriminate each Higgs sector.
-Type-II 2HDM: qq → HA → 4b, Type-X 2HDM: qq → HA → 4τ, 2τ + 2μ
- Decay of H++ in HTM: H++ → l+l+ (Small vΔ), H++ → W+W+ (Large vΔ),
H++ → H+W+ (Large mass splitting).
Indirect way: Precise test of the Higgs couplings (hγγ and hZγ)
h → γγ and h → Zγ decay modes are sensitive to the new physics models.
→ Measuring both modes may be useful.
We focused on effects of charged scalar boson which are introduced
from various extended Higgs sectors.
Class I: H±, Class II: H± + H±±, Class III: H1± + H2±
When a charged scalar mass is taken to be around 200 GeV, h → γγ
can be enhanced ~ 15 % , ~ 80 % and ~ 30 % in Class I, II and III, respectively
compared with the SM prediction.
Scalar loop function
Potential in models Class III
In models w/ φSM + S1+ + S2+, φSM + D1 + D2, φSM + T10 + T20 , μ is absent.
In models w/ φSM + D + S, φSM + D + T0, M3 and λ3 are absent.
Heavy case (mS = 400 GeV )
Class I
Class II
Dubinin, Schreiber, Vologdin, Eur. Phys. J. C30 (2003)
Measurement hZγ coupling at linear colliders
h → Zγ decay process has been analyzed via the vector boson fusion process
at the future linear collider.
mh = 120 GeV, root(s) = 500 GeV, integrated L = 1 ab-1
Accuracy of ΔBR (h → Zγ) is expected to be 48 %
By using polarized beam, this would be improved to be 29 %.
Branching ratios of H+, H and A
★ The H+ → f0 W+ mode can be dominant
in the case of Δm ≠ 0.
★ The f0 → bb mode can be dominant
when vΔ > MeV.
CP-even Higgs decay in the case with
sin(β-α) = 1, mA = mH =150 GeV
Type II (MSSM-like)
Type X
Type-X 2HDM simulation
Kanemura, Tsumura, Yokoya, PRD 85
b→sγ
W－
H－
γ
b
Type-II, Y
Type-I, X
t
γ
s
b
t
s
Barger, Hewett, Phillips PRD 41 (1990)