1. Introduction 2. Model 3. Analysis 4. Summary 1. Introduction - - PowerPoint PPT Presentation
DM from om chir hiral al U( U(1) 1) X dar dark k sect ector or And nd diphot diphoton on exces cess Takaaki Nomura (KIAS) Based on: P.Ko, T.N. arXiv:1601.02490 (to be published in PLB) and work in progress 2016-05-07 17 th New Higgs
DM from
hiral al U( U(1) 1)X dar dark k sect ector
And nd diphot diphoton
cess Takaaki Nomura (KIAS)
Based on: P.Ko, T.N. arXiv:1601.02490 (to be published in PLB) and work in progress
2016-05-07 17th New Higgs Working Group @ Toyama
Diphoton excess at 750 GeV
Both ATLAS and CMS observed bump
(Local significance)
3.6 σ : ATLAS 2.6 σ : CMS
ATLAS-CONF-2015-081, CMS-PAS-EXO-15-004
Diphoton excess at 750 GeV
Both ATLAS and CMS observed bump
(Local significance)
3.6 σ : ATLAS 2.6 σ : CMS
ATLAS-CONF-2015-081, CMS-PAS-EXO-15-004
Updated results are presented at the Moriond 2016 3.9 (2.0) σ : ATLAS 3.4 (1.6) σ : CMS Local (Global Significance)
CMS added 0.6 fb-1 13 TeV data and combined with 8 TeV result
Diphoton excess at 750 GeV (ATLAS)
Spin 0 Spin 2 ATLAS Collaboration, ATLAS-CONF-2016-018.
Diphoton excess at 750 GeV (ATLAS)
Spin 0 Spin 2
Ø mX~750 GeV Ø Width can be narrow or wide Ø Local significance 3.9 (3.6)σ for spin 0(2) Ø Global significance 2.0(1.8)σ for spin 0(2)
ATLAS Collaboration, ATLAS-CONF-2016-018.
Diphoton excess at 750 GeV (ATLAS)
Consistency between 8 TeV and 13 TeV result Ø Spin 0 : 1.2 (2.1)σ for gg(qq) prodcution Ø Spin 2 : 2.7 (3.3)σ for gg(qq) prodcution Deviation between 8 TeV and 13 TeV result
Diphoton excess at 750 GeV (CMS)
CMS collaboration CMS-PAS-EXO-16-018
Spin 0 Spin 2
Ø Evaluated through likelihood scan vs equivalent 13TeV cross-section at mX = 750GeV under both spin (narrow-width) hypotheses
Combined with 8 TeV data
Diphoton excess at 750 GeV (CMS)
CMS collaboration CMS-PAS-EXO-16-018
Spin 0 Spin 0 Spin 2 Spin 2
Diphoton excess at 750 GeV (CMS)
Ø mX~750 GeV Ø Narrow width is preferred Ø Local significance 3.4σ (maximum) Ø Global significance 1.6σ
Spin 0 Spin 2
1.introduction
v Constraints from other modes arXiv:1604.06446 (Franceschini et. al.)
How we can interpret the diphoton excess?
Ø Cross section to produce a new particle φ
σ (pp →ϕ)BR(ϕ →γγ) ≈ 3−10 fb
Ø Width of φ Best fit value by ATLAS : Γ~45 GeV (not so significant) CMS : Narrow width is preferred (<< 10 GeV) Ø It could be new particle : spin 0 or 2
1.introduction
Narrow width? Or wide width?
Spin 0 is preferred but spin 2 is not excluded
Width can be 0-100 GeV Ø No significant associated events (other jets, leptons etc.)
One scenario: gluon fusion + diphoton decay via loop
Production: gluon fusion Diphoton decay channel
g g γ γ
Colored particle Charged particle
One scenario: gluon fusion + diphoton decay via loop
Production: gluon fusion Diphoton decay channel
g g γ γ
Colored particle Charged particle
It is not easy to get σ(gg→ΦNew)BR(ΦNew→γγ)~5 fb
Ex) Two Higgs doublet Model (Type-II)
σ(gg→H)~850 fb × cot2β
BR(H→γγ)~O(10-5)
σ(gg→A)~850 fb × 2cot2β
BR(A→γγ)~O(10-5)
We need exotic colored and/or charged particles
Let us discuss simple case of (SM) singlet scalar boson + exotic particles
(Angelescu, Djouadi, Moreau arxiv:1512.0492)
Simple way: vector-like fermion + singlet scalar
Yukawa coupling and masses of VLF are arbitrary
v Lets consider F to be chiral under dark gauge symmetry v F is massless before dark gauge symmetry breaking v These Yukawa coupling and mass are related
Simple way: vector-like fermion + singlet scalar
Yukawa coupling and masses of VLF are arbitrary
v Lets consider F to be chiral under dark gauge symmetry v F is massless before dark gauge symmetry breaking v These Yukawa coupling and mass are related
Let us discuss diphoton excess via Dark sector
Dark sector : charged under dark (extra) gauge symmetry
SM+U(1)X + New fermions and scalars with U(1)X charge v New fermions are VL under SM but chiral under U(1)X v Relevant couplings are related to new gauge coupling gX v 750 GeV scalar can decay into new massive gauge boson (Z’) v DM candidate is contained in a model
New fermions get masses after U(1)X breaking
Model : local U(1)X model with exotic particles
Contents in dark sector（anomaly free） X,N : DM candidate
(3 generations of fermions)
Model : local U(1)X model with exotic particles
Contents in dark sector（anomaly free） New Lagrangian
L
Y = yEELERΦ+ yNNLNRΦ* + yUULURΦ* + yDDLDRΦ
+yEeELeRX + yUuULuRX* + yDdDLdRX + h.c. V = µ 2 H
2 + λ H 4 +µΦ 2 Φ 2 +µX 2 X 2
+λΦ Φ
4 + λX X 4 + λHΦ H 2 Φ 2 + λHX H 2 X 2 + λXΦ X 2 Φ 2
X,N : DM candidate
(3 generations of fermions)
Contents in dark sector（anomaly free） New Lagrangian
L
Y = yEELERΦ+ yNNLNRΦ* + yUULURΦ* + yDDLDRΦ
+yEeELeRX + yUuULuRX* + yDdDLdRX + h.c. V = µ 2 H
2 + λ H 4 +µΦ 2 Φ 2 +µX 2 X 2
+λΦ Φ
4 + λX X 4 + λHΦ H 2 Φ 2 + λHX H 2 X 2 + λXΦ X 2 Φ 2
Giving mass for new fermions + gg fusion and γγ decay of Φ
X,N : DM candidate
Model : local U(1)X model with exotic particles
(3 generations of fermions)
Contents in dark sector（anomaly free） New Lagrangian
L
Y = yEELERΦ+ yNNLNRΦ* + yUULURΦ* + yDDLDRΦ
+yEeELeRX + yUuULuRX* + yDdDLdRX + h.c. V = µ 2 H
2 + λ H 4 +µΦ 2 Φ 2 +µX 2 X 2
+λΦ Φ
4 + λX X 4 + λHΦ H 2 Φ 2 + λHX H 2 X 2 + λXΦ X 2 Φ 2
Decay of new fermions F F → X fSM Giving mass for new fermions + gg fusion and γγ decay of Φ
X,N : DM candidate
Model : local U(1)X model with exotic particles
(3 generations of fermions)
Gauge Symmetry breaking and Z’
v VEVs of scalar fields
H = 1 2 v, Φ = 1 2 vφ v ≈ −µ 2 λ , vφ ≈ −µΦ
2
λΦ λHΦ <<1
( )
v Masses of Z’ and new fermions
mZ '
2 ≈ (a + b)2gX 2vφ 2,
mF = yF 2 vφ yF = 2(a + b)gXmF mZ ' λΦ = 2mφ
2gX 2
m
Z '
2
v Z’ decays through small Z-Z’ mixing U(1)X is broken by <Φ>
We assume H-Φ mixing is negligible
Massive Z’
Φ = (vφ +φ +iGX ) / 2
BRs of Z’ in model
q q e e Μ Μ Ν Ν Τ Τ
150 200 250 300 350 0.05 0.10 0.20 0.50 1.00
mZ'GeV BR
v Z’ decays into SM fermions via kinetic mixing of U(1)Y and U(1)X
fSM fSM Z’ Z
BRs of Z’ in model
q q e e Μ Μ Ν Ν Τ Τ
150 200 250 300 350 0.05 0.10 0.20 0.50 1.00
mZ'GeV BR
v Z’ decays into SM fermions via kinetic mixing of U(1)Y and U(1)X v Yukawa interaction XFf may change the BRs (we ignore in this talk)
fSM fSM Z’ Z fSM fSM Z’ X F F
Stability of Dark Matter candidate
v Accidental Z2 symmetry after U(1)X breaking FL, FR, X : Z2 odd Others : Z2 even Neutral Z2 odd particle can be DM candidate : X, N
Note:
There can be a term : ΦnX (Φn X*) a/(a+b)=n for gauge invariance : suitable choice of a, b can make a/(a+b) non-integer (absolutely stable), or make n very large (long-lived X). We choose a~b~1 for simplicity
Relic density of the Dark Matter X, N
XX → Z’Z’ NN → Z’Z’
We focus on the annihilation processes
N N N N X X X X Z’ Z’ Z’ Z’ Z’ Z’ Z’ Z’
Relevant gauge interactions
Search for the parameter region satisfying observed relic density
0.1159 ≤ ΩDh2 ≤ 0.1215
P.A.R. Ade et al [Planck Collaboration] (2013)
Planck data (90% C.L.) ΩD is Calculated with MicrOMEGAs
( G. Belanger, F. Boudjema, A. Pukhov and A. Semenov)
Relic density of the Dark Matter X
v For non-zero λXΦ s-channel and t(u)-channel interfere v The resonant effect around mX ~ mΦ/2 for non-zero λXΦ v gx = 0.2 ~ 0.5 can provide with relic density (mX = 120~500 GeV)
ΛX 0 MN 600 GeV
500 200 300 150 0.50 0.20 0.30 0.15 0.70
mXGeV gX
MN 600 GeV gx 0.1 gx 0.3
500 200 300 150 0.02 0.05 0.10 0.20 0.50 1.00 2.00
mXGeV ΛX
Relic density of the Dark Matter N
v s-channel and t(u)-channel always interfere v The resonant effect around mX ~ mΦ/2 v gx < 0.5 can provide with relic density (mX = 120~500 GeV)
mX 600 GeV
500 200 300 150 0.50 0.20 0.30 0.15 0.70
mNGeV gX
Direct detection constraint of DM
Possible DM-nucleon scattering processes
v Z’ exchanging suppressed by small Z-Z’ mixing v The SM Higgs exchanging suppressed by small λXH v φ exchanging non-trivial if λXΦ is not zero
XXGG effective interaction X-nucleon scattering cross section fTG is the numerical value
Ø In current case σDN < 10-48 cm2
(F. Giacchino, A. Ibarra, L. L. Honorez, M. H. G. Tytgat and S. Wild, JCAP 1602, no. 02, 002 (2016) [arXiv:1511.04452 [hep-ph]] )
Our scenario to explain diphoton excess
l Production of spin-0 particle φ Gluon fusion via new colored fermion loop l Decay of φ Ø Z’Z’ mode is dominant Width is wide Ø gg mode is dominant (mZ’>mφ/2) Width is narrow We then discuss some constraints
Gluon fusion and diphoton decay of φ via new fermion loop Decay widths
gg → φ Gluon fusion and decay modes of φ
Lφgg = αs 8π (a + b) 2gX mZ '
F=U,D
A
1/2(τ F)
⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟φGaµνGµν
a
Γ(φ →γγ) = α 2mφ
3
256π 3 Nc
F (a + b)gXQF 2
mZ ' A
1/2(τ F) F
2
Γ(φ → Z 'Z ') = (a + b)2gX
2mφ 3
32πmφ 1− 4mZ '
2
mφ
2
× mφ
4 − 4mφ 2mZ ' 2 +12mZ ' 4
mZ '
4
. . .
BRs and gluon fusion are function of gX and mZ’
Gluon fusion and diphoton decay of φ via new fermion loop Branching fraction of φ
gg → φ Gluon fusion and decay modes of φ
Lφgg = αs 8π (a + b) 2gX mZ '
F=U,D
A
1/2(τ F)
⎛ ⎝ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟φGaµνGµν
a
mX 350 GeV gg Z ' Z ' XX ΓΓ ZΓ
0.2 0.4 0.6 0.8 1.0 104 0.001 0.01 0.1 1
gX BR
gg ΓΓ ZΓ
0.2 0.4 0.6 0.8 1.0 104 0.001 0.01 0.1 1
gX BR
mZ ' = 300GeV, mX = 350GeV mZ ' = 400GeV, mX = 450GeV
yU,D 4 Π Λ 4 Π 10 7 5 3
150 200 250 300 350 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
mZ'GeV gX
yU,D 4 Π Λ 4 Π 50 40 30 20 10 5 1
150 200 250 300 350 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
mZ'GeV gX
Cross section and widht of φ (mZ’ < mφ/2)
σ (gg →φ)BR(φ →γγ) Γφ
v ~5 fb cross section with gX=0.3~0.5 and mZ’=120~360 GeV v Decay width is relatively large: O(10~50) GeV
[fb] [GeV]
(a~b~1) {MU,D, ME,N,MX,λXΦ} = {800 GeV, 400 GeV, 350 GeV, 0.075}
Discussion: Cross section of φ production (mZ’ < mφ/2)
yU,D 4 Π Λ 4 Π Kgg 2.0 40 30 20 10 5 1
150 200 250 300 350 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
mZ'GeV gX
l Large cross section of O(10) pb l ~1/5 for 8 TeV case l No direct constraints for pp→φ→Z’Z’→4fSM l Z’ width is very narrow
[pb] Γ/M<10-6 due to small Z-Z’ mixing
(a~b~1)
13 TeV
{MU,D, ME,N,MX,λXΦ} = {800 GeV, 400 GeV, 350 GeV, 0.075}
2 jets 2 leptons 4 jets 4 leptons
150 200 250 300 350 1 5 10 50 100 500 1000
mZ'GeV BR2ΣggΦ
2 jets 2 leptons 4 jets 4 leptons
150 200 250 300 350 1 5 10 50 100 500 1000
mZ'GeV BR2ΣggΦfb
Discussion: Cross section of φ production (mZ’ < mφ/2)
Combined with Z’ decay branching fractions
13 TeV 10 pb 8 TeV 2 pb
Leptonic modes provide strongconstraint
2 jets 2 leptons 4 jets 4 leptons
150 200 250 300 350 1 5 10 50 100 500 1000
mZ'GeV BR2ΣggΦ
2 jets 2 leptons 4 jets 4 leptons
150 200 250 300 350 1 5 10 50 100 500 1000
mZ'GeV BR2ΣggΦfb
Discussion: Cross section of φ production (mZ’ < mφ/2)
Combined with Z’ decay branching fractions
13 TeV 10 pb 8 TeV 2 pb
Leptonic modes provide strongconstraint It could be avoid by changing BRs
fSM fSM Z’ X F F
0.1 0.2 0.3 0.4 0.5 0.6 1 2 5 10 20 50 100
gX
ΣggΦBRΦΓΓfb
0.2 0.4 0.6 0.8 1.0 0.02 0.05 0.10 0.20 0.50 1.00 2.00
gX
ΦGeV
(a~b~1) {MU,D, ME,N,MX,MZ’,λXΦ,} = {800 GeV, 400 GeV, 450 GeV,400 GeV, 0.075} v ~5 fb cross section with gX=0.1~0.2 for mZ’=400 GeV v Decay width is very narrow
Discussion: Cross section of φ production (mZ’ > mφ/2)
0.1 0.2 0.3 0.4 0.5 0.6 200 500 1000 2000 5000
gX
ΣggΦfb
l O(1) pb for excess l ~1/5 for 8 TeV case l ~almost decay into gg l Constraint is not strong
Summary and Discussions
² SM+U(1)X charged dark sector: new fermions are chiral under U(1)X ² 750 GeV scalar boson(φ) from U(1)X breaking scalar ² Diphoton excess: Production and decay from new fermion loop ² Wide width of φ: O(10~50) GeV by φ→Z’Z’ ² Narrow width for mZ’ < mφ/2 ² Signature: We need detailed analysis for φ→Z’Z’ (Z’→SM fermions) ² DM relic density can be explained
Loop functions in the partial decay widths A
1/2(τ ) = 2τ[1+(1−τ )(sin−1(1/
τ ))2] (τ ≥1) AF = α 2πsWcW −4yFQF mF (TF
3 − sW 2 QF)[I1(τ,λ)− I2(τ,λ)]
τ i = 4m
Fi
2
mS
2 ,
λi = 4m
Fi
2
mZ
2
Φ partial widths (1)
Φ partial widths (2)
Stability of potential
yF 1.2
10.0 5.0 2.0 3.0 1.5 15.0 7.0 1 2 3 4 5 Μ TeV Λ
RG flow of λΦ