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Introduccion a la Fisica del Higgs(2do Sermon)
J. Lorenzo Diaz-CruzFCFM-BUAP (Mexico)EFF- UA Sinaloa, 2014
August 8, 2014
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 1 / 41
1 Motivation- Particle Physics
2 THE Standard Model - Higgs sector
3 SM Higgs Properties and its detection at LHC
4 The Higgs mass and Physics Beyond the SM
5 The Higgs and the Roots of Physics
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 2 / 41
The Standard Model (SM)
Matter is made of quarks and leptons,
Forces are associated with gauge symmetries,
Masses arise from spontaneous symmetry breaking (SSB),
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 3 / 41
In the SM a Higgs doublet can work (Minimal)
Around the minimum: φ0 = 1√2(v + h+ iχ)
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 4 / 41
SM Higgs interactions
SM lagrangian for a Higgs doublet Φ = (φ+, φ0) includes:
Gauge ints. → Gauge boson masses,
i.e. LHV = (DµΦ)†(DµΦ)
Yukawa sector → fermion masses,
i.e. LY = YuQLΦuR, etc.
Higgs potential V (Φ) → SSB and Higgs mass,
i.e. V (Φ) = λ(|Φ|2 − v2)2,
One unknown parameter λ,- it determines Higgs mass: m2
h = 212λv
2
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 5 / 41
Higgs couplings
(hV V ) :2m2
Vv , (hff) :
mf
v
(hhh) : 32λv, (hhhh) : 3
2λ
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 6 / 41
Busqueda de efectos directos del Higgs
Busqueda en LEP2: e+e− → Z + h → mh > 115GeV
Busqueda en Tevatron: excluyo 160 < mh < 170 GeV
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 7 / 41
Efectos indirectos del boson de Higgs
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 8 / 41
Radiative Constraints on mh:
→ light Higgs, i.e. with a mass of order of EW scale, ( mφSM' v).
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 9 / 41
SM Higgs Phenomenology- Decays
First, one need to study decay modes for a light Higgs:
h→ bb,
h→ cc, ss,
h→ τ+τ−, µ+µ−,
h→ γγ (top and W loops) (Ellis, Gaillard, Nanopoulos),
h→ gg (top loop) (Georgi, Glashow, Machacek, Nanopoulos)
h→WW ∗, ZZ∗ (Keung, Marciano)
h→ tt
B.R.(h→ XX) =Γ(h→ XX)
Γtotal(1)
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 10 / 41
How does a particle decays?
Schroedinger equation: H|ψ >= i ddt |ψ >The Hamiltonian for an unstable particle at rest: H = M − iΓ
2 ,
ψ(t) = ψ(0)e−iHt = ψ(0)e−iMte−Γt/2
|ψ|2 = |ψ(0)|2 e−Γt
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 11 / 41
SM Higgs decay into fermion pairs
For the decay: h(p)→ f(p1)f(p2)
M(h→ ff) =−igmf
2mWu(p1)(1)v(p2), (2)
Kinematics:
Energy-momentum conservation: p = p1 + p2,
In rest frame of Higgs: p = (mh, 0),
p2 = m2h, p2
1 = m2f = p2
2,
p.p1 = mhE1, p.p2 = mhE2, 2p1.p2 = m2h − 2m2
f ,
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 12 / 41
SM Higgs decay into fermion pairs
dΓ(h→ ff) =1
8π2mh|M(h→ ff)|2d2(PS) (3)
|M |2 =m2f
v2Tr(γµp1µ +mf )(γνp2ν +mf ) =
m2f
v24p1.p2 (4)
Then,
Γ(h→ ff) = Ncg2mh
32π
m2f
m2W
[1− 4m2f
m2h
]3/2 (5)
where:
Nc = 3 (1) for quarks (leptons),
The exponent 3/2 signals that the Higgs is an SCALAR (would be1/2 if it were a pseudoscalar),
mf = mf (Q2) (RGE), ex. mb(MZ) ' 3.5 GeV,
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 13 / 41
Higgs Decay widths
Γ(h→ ff) = Ncg2mh
32π
m2f
m2W
[1− 4m2f
m2h
]3/2 (6)
Γ(h→ gg) =α2sg
2m3h
128π3m2W
|Ig(rx)|2 (7)
Γ(h→ γγ) =α2g2m3
h
1024π3m2W
|Iγ(rx)|2 (8)
Γ(h→WW ∗) =3g4mh
512π3F3b(mW /mh) (9)
where rx = 4m2x/m
2h, and analogous expression can be written for:
Γ(h→ γZ) and Γ(h→ ZZ∗)
Tarea: 3) Estimar BR(h→ ττ), BR(h→ µµ),
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 14 / 41
Higgs B.R.’s
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 15 / 41
Higgs production at pp/pp colliders (LHC/Tevatron)
σhad =∑ij
∫fi(x1, Q
2) fi(x2, Q2) dx1dx2 σparton (10)
σgg =
∫fg(x1, Q
2) fg(x2, Q2) dy
π2Γ(h→ gg)
8m2h
(11)
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 16 / 41
Higgs cross sections
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Higgs cross sections → No. ef events
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Higgs cross sections → No. ef events
Total Production cross sectionσ ∗Br = σ(pp→ h+X)×BR(h→ Y Y )
Need to look for interesting modes,
No. of events= σ ∗Br ∗ I.L.Integrated Luminosity= No. of colisions per unit area,
ex. With IL(LHC) = 13 fb−1 = 13× 103pb−1 andσ(pp→ h→ γγ) = 4× 10−2 pb for mh =' 125 GeV→ 520 Events!
Signal vs Background: only a fraction of those 500’s events will bedetected,
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Higgs cross sections
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Higgs search- LHC
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Higgs search- LHC
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Higgs search- LHC
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Higgs search- LHC
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 24 / 41
The Higgs-dependence day
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The Higgs-dependence day
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Higgs search- LHC
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 27 / 41
Higgs search- CMS -ZZ Channel
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Higgs search- LHC
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 29 / 41
Higgs search- LHC
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Mexican hat and BEH mechanism
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Then what?
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Higgs identity: ghXX = cX gsmhXX
In the SM: cX = 1,
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SM Higgs identity: gsmhXX = MX
v
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 34 / 41
Higgs Couplings in 3+1 HDM (JLDC)
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 35 / 41
The Universal Higgs fit - P. Giardino et al.,arXiv:1303.3570 [hep-ph]
Under the small deviations approximation:
cX = (1 + εX) (12)
From a fit to all observables (signal strengths), and assuming no newparticles contribute to the loop decays hgg and hγγ, they get:
hZZ (hWW ): εZ = −0.01± 0.13 (εW = −0.15± 0.14),
hbb: εb = −0.19± 0.3,
hττ : ετ = 0± 0.18
htt (from hgg): εt = −0.21± 0.23
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Higgs parity: hff or hfγ5f?
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 37 / 41
Higgs and Flavor ViolationOnly hff or also possible hfifj?, ex. h→ τµ (Diaz-Cruz and collab.),
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4. The Higgs mass and Physics Beyond the SM
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 39 / 41
5. The Higgs and the Roots of Physics
(BUAP) Introduccion a la Fisica del Higgs (2do Sermon)August 8, 2014 40 / 41