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Higgs decays to γγ and Zγ in models with Higgs extensions
Kei Yagyu (National Central U.)
Academia Sinica, September 14th
Collaboration with Cheng-Wei Chiang (National Central U.)
arXiv: 1207.1065 [hep-ph]
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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
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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 ??
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Higgs sector in the SM
All the masses of particles are given by the Higgs VEV.
V (φ)
φ0φ+
Higgs potential Φ: isospin SU(2) scalar doublet
f +
f 0 F =
Origin of MassGauge boson mass
SU(2)L×U(1)Y → U(1)EM
Higgs VEV
Fermion mass
<F>
<F>
<F>
<F>
F
F
<F>f
f
V
V
g2 y λ
Higgs mass
mV2 = g2v2 mf = y v mh
2 = λv2
Physical state: Only one neutral component h
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Higgs sector in the SM
All the Higgs interactions are proportional to the mass
V (φ)
φ0φ+
Higgs potential Φ: isospin SU(2) scalar doublet
f +
f 0 F =
Higgs InteractionGauge interaction
SU(2)L×U(1)Y → U(1)EM
Higgs VEV
Yukawa interaction Self interaction
F
F
F
F
F
F
Ff
f
V
V
g2 y λ
∝ mV2 / v2 ∝ mh
2/v2∝ mf / v
Physical state: Only one neutral component h
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Higgs search at collider experiments
Higgs boson
・・・
e+e- (LEP, ILC), pp (Tevatron),
pp (LHC),…
Production Decay
X
Depends on
Collision particle, Center of mass energy, …
Theory(Model)
Theory(Model)
Beam Detector
Detector performance, …
We should know the production and decay property of the Higgs boson.
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Branching fraction
hf
f
hW+, Z
W-, Z
hγ, g
γ, g
‣ bb mode: Large branching ratio, but huge background ‣ γγ, ZZ(*) → 4 lepton mode: Tiny branching ratio, but small background
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Higgs boson production at the LHC
Gluon Fusion ~ 10 pb
Vector Boson Fusion ~ 1 pb
W/Z association
Top quark association
V. Sharma, talk at Moriond (2011)
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‣ The Higgs-like particle has been found at around 126 GeV at the LHC with 5σ.
Historic Milestone but only the Beginning.
h → ZZ* → 4 leptonh → γγ
R. Heuer, July 4th, CERN
Current states of the Higgs search at the LHC
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Current states of the Higgs search at the LHCSignal strength (σobs/σSM) in each mode
1207.7235 [hep-ex], ATLAS1207.7214 [hep-ex], CMS
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Current states of the Higgs search at the LHCSignal strength (σobs/σSM) in each mode
H → ZZ and H→ WW modes are good agreement to the SM prediction.
1207.7235 [hep-ex], ATLAS1207.7214 [hep-ex], CMS
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Current states of the Higgs search at the LHCSignal strength (σobs/σSM) in each mode
Obs. H → γγ signal seems to be large compared to the SM prediction.
1207.7235 [hep-ex], ATLAS1207.7214 [hep-ex], CMS
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Current states of the Higgs search at the LHC
1207.7235 [hep-ex], ATLAS1207.7214 [hep-ex], CMS
Signal strength (σobs/σSM) in each mode
H → ττ and H → bb modes have large uncertainty. At CMS, H → ττ mode did not seem to be discovered yet.
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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!
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Extended Higgs sector
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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 SMExtended Higgs sectors Determine
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What is the true Higgs sector?There are hints to determine the structure of the Higgs sector.
1. Electroweak rho parameter ρexp = 1.0008
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)
-0.0007+0.0017
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
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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
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Testing an extended Higgs sector at colliders
We discuss the 2 Higgs doublet model and the Higgs triplet model as important examples.
• 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
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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) - Tiny neutrino masses can be generated via the type-II seesaw mechanism.
Cheng, Li (1980); Schechter, Valle, (1980); Magg, Wetterich, (1980);Mohapatra, Senjanovic, (1981).
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Higgs potential in the 2HDMThe Higgs potential under the softly broken Z2 sym. (Φ1 → + Φ1, Φ2 → -Φ2)
Physical scalar states: 8-3 = 5 Tanβ = v2/v1
Mass formulae (sin(β-α) ~1 )
SM-like Higgs boson Extra Higgs bosons
Goldstone bosons
CP-even Higgs Charged Higgs CP-odd Higgs
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Barger, Hewett, Phillips PRD 41 (1990)
Grossman NPB 426 (1994)
ud
Φ 2
eΦ1u
d
Φ 2
e
ud
Φ 2
e
Φ1
Type-I Type-II (MSSM)
ud
Φ 2
eΦ1
Type-X Type-Y
Four types of the Yukawa interaction
Aoki, Kanemura, Tsumura, Yagyu, PRD 80, 2009
t sb
γW - H -
γ
b t s
Bs → sγ Imposing Z2 symmetry → Only one of the two doublet couples to each fermion.
In the Type-I and Type-X 2HDM, a light charged Higgs boson can be allowed.
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CP-odd Higgs (A) decay in the case withsin(β-α) = 1, mA = mH =150 GeV
Type II (MSSM-like) Type X
(μ+)
(μ-)
Kanemura, Tsumura, Yokoya, PRD 85 (2012)
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Higgs potential in the HTMThe Higgs potential
Physical scalar states: 10 -3 = 7
NG bosonsDoubly-charged Higgs
CP-even Higgs Singly-charged Higgs CP-odd Higgs
Mass formulae (vΔ/vφ << 1 )Triplet-like
SM-like
A, H
H+
H++A, H
H+
H++
Case I (λ5 >0) Case II (λ5<0)
Mass2 Mass2
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Branching ratio of H++
Phenomenology with the mass splitting is drastically different from that without the mass splitting
Without mass splitting With mass splitting (mH++ - mH+ = 10 GeV)
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Mass reconstructionqq’ → H++H- → (l+l+ννbb)(jjbb) qq’ → H+H → (l+νbb)(bb) qq → HA → (bb)(bb)
8.0 fb (14 TeV) 2.8 fb (7 TeV)
33 fb 12 fb
130 fb 42 fb
All the masses of the Δ-like scalar bosons may be reconstructed.
vΔ = 10-2 GeV
MT
MT
MT, Minv
mH++ mH+ mH, mA
Signal only
hH, AH+
H++
114 GeV119 GeV130 GeV
140 GeV
Aoki, Kanemura, KY, PRD85(2012)
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Higgs decays into the γγ and Zγ
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Testing an extended Higgs sector at colliders
We discuss Higgs decays into the diphoton (hγγ) andthe Z + photon (hZγ).
• 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
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Higgs to the diphoton channel
The signal strength σOBS/σSM exceeds 1 at the both experiments: 1.56± 0.43 (CMS), 1.9±0.5 (ATLAS).
CMS, ICHEP ATLAS, ICHEP
‣ 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.
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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
Cahn, Chanowitz, Fleishon, (1979); Bergstrom, Hulth, (1985)
Ellis, Gaillard, Nanopoulos, (1976) ;Ioffe, Khoze, (1978); Shifman, Vainshtein, Voloshin, Zakharov, (1979)
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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
‣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 effectsare destructive with each other.
Cahn, Chanowitz, Fleishon, (1979); Bergstrom, Hulth, (1985)
Ellis, Gaillard, Nanopoulos, (1976) ;Ioffe, Khoze, (1978); Shifman, Vainshtein, Voloshin, Zakharov, (1979)
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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)
‣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 effectsare destructive with each other.
How these predictions are changed by new physics effects?
‣Decay rate
Cahn, Chanowitz, Fleishon, (1979); Bergstrom, Hulth, (1985)
Ellis, Gaillard, Nanopoulos, (1976) ;Ioffe, Khoze, (1978); Shifman, Vainshtein, Voloshin, Zakharov, (1979)
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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.
Spin 0 Spin 1/2 Spin 1
Ex. Charged Higgs boson, Squark, Slepton…
Ex. 4th generation fermion, Chargino… Ex. W’ boson…
(Z)
In this talk, we focus on modes with extended Higgs sector, where new charged scalar bosons are introduced to the SM.
(Z) (Z)
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Previous works and our workThere are several papers where the h→γγ mode is studied in an extended Higgs sector.
・ 2 Higgs doublet model
・ Higgs triplet model
・ Zee model (2HDM + charged singlet)
Posch 2011;Arhrib, Benbrik, Gaur 2012;Ferreira, Santos, Sher, Silva 2012
Arhrib, Benbrik, Chabab, Moultakae, Rahilib 2012;Kanemura, Yagyu 2012; Akeroyd, Moretti 2012
Kanemura, Kasai, Lin, Okada, Tseng, Yuan 2000
We study the h→γγ(Z) more comprehensive way in various extended Higgs sectors.
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Classes of extended Higgs sectors ‣ 3 classes of extended Higgs sectors.
Class I : Models with one singly-charged scalar boson
Class II : Models with one singly-charged and one doubly-charged scalar boson
Class III : Models with two singly-charged scalar bosons
Ex. 2HDM
Ex. Higgs triplet model, Zee-Babu model
Ex.: Radiative seesaw models (Zee model, Kauss-Nasri-Trodden model, Aoki-Kanemura-Seto model)
SM H±
SM H± H±±
SM H1± H2
±
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List of models
‣ We consider Higgs sectors with additional SU(2)L singlets (S), doubles (D) and triplets (T).
Class I Class II Class III
Singlet
Doublet
Triplet
There are 13 models depending on the # of scalar fields.
(Y = 1)
(Y = 2)
(Y = 1/2)
(Y = 0)
(Y = 1)
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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.
Same as the SMOnly h→γγ and h→Zγ decay modes can be modified significantly. The other decay rates are almost the same as the SM.
h
・・・Production Decay
X
Modified decay rate directly affects to the number of events.
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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.
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Relevant terms in Class I and II
⊃
⊃
Φ : SM doublet
: Extra scalar field1, 2
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Relevant terms in Class III
M1 = M2 = M3
= M
M1 = M2 = M3
= M
Mixing angle:⊃=
≠
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Results (Class I and Class II)
Class I
Class II
ΔB (h → X) = [Br(h → X)NP - Br(h → X)SM]/ Br(h → X)SM
mH+ = mH++ = 200 GeV
Not allowed by the vacuum stability bound.
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Results (Class I and Class II)
Class I
Class II
R = Br(h → Zγ)NP/ Br(h → γγ)NP
mH+ = mH++ = 200 GeV
Not allowed by the vacuum stability bound.
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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
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Results (Class III)mH1+ = 200 GeV, mH2+ = 300 GeV, M = 308 GeV
R = Br(h → Zγ)NP/ Br(h → γγ)NP
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Summary• To know the true Higgs sector → To determine physics beyond the SM.1. 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). 2. 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.
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Scalar loop function
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Potential in models Class III
In models w/ φSM + S1+ + S2
+, φSM + D1 + D2, φSM + T10 + T2
0 , μ is absent.
In models w/ φSM + D + S, φSM + D + T0, M3 and λ3 are absent.
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Heavy case (mS = 400 GeV )
Class I
Class II
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Measurement hZγ coupling at linear colliders
Dubinin, Schreiber, Vologdin, Eur. Phys. J. C30 (2003)
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 %.
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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.
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CP-even Higgs decay in the case withsin(β-α) = 1, mA = mH =150 GeV
Type II (MSSM-like) Type X
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Kanemura, Tsumura, Yokoya, PRD 85
Type-X 2HDM simulation
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b→sγ
Type-I, X
Type-II, Y
t sb
γW -
H -
γ
b t s
Barger, Hewett, Phillips PRD 41 (1990)