Vector-like quarks t and partners

Vector-like quarks
t′ and partners
Luca Panizzi
University of Southampton, UK
Outline
1
Motivations and Current Status
2
Couplings and constraints
3
Signatures at LHC
Outline
1
Motivations and Current Status
2
Couplings and constraints
3
Signatures at LHC
What are vector-like fermions?
and where do they appear?
The left-handed and right-handed chiralities of a vector-like fermion ψ
transform in the same way under the SM gauge groups SU (3)c × SU (2)L × U (1)Y
What are vector-like fermions?
and where do they appear?
The left-handed and right-handed chiralities of a vector-like fermion ψ
transform in the same way under the SM gauge groups SU (3)c × SU (2)L × U (1)Y
Why are they called “vector-like”?
What are vector-like fermions?
and where do they appear?
The left-handed and right-handed chiralities of a vector-like fermion ψ
transform in the same way under the SM gauge groups SU (3)c × SU (2)L × U (1)Y
Why are they called “vector-like”?
g LW = √ J µ+ Wµ+ + J µ− Wµ−
2
Charged current Lagrangian
What are vector-like fermions?
and where do they appear?
The left-handed and right-handed chiralities of a vector-like fermion ψ
transform in the same way under the SM gauge groups SU (3)c × SU (2)L × U (1)Y
Why are they called “vector-like”?
g LW = √ J µ+ Wµ+ + J µ− Wµ−
2
Charged current Lagrangian
SM chiral quarks: ONLY left-handed charged currents
(
µ+
JL = ūL γ µ dL = ūγ µ (1 − γ5 )d = V − A
µ+
µ+
J µ+ = JL + JR
with
µ+
JR = 0
What are vector-like fermions?
and where do they appear?
The left-handed and right-handed chiralities of a vector-like fermion ψ
transform in the same way under the SM gauge groups SU (3)c × SU (2)L × U (1)Y
Why are they called “vector-like”?
g LW = √ J µ+ Wµ+ + J µ− Wµ−
2
Charged current Lagrangian
SM chiral quarks: ONLY left-handed charged currents
(
µ+
JL = ūL γ µ dL = ūγ µ (1 − γ5 )d = V − A
µ+
µ+
J µ+ = JL + JR
with
µ+
JR = 0
vector-like quarks: BOTH left-handed and right-handed charged currents
µ+
µ+
J µ+ = JL + JR = ūL γ µ dL + ūR γ µ dR = ūγ µ d = V
What are vector-like fermions?
and where do they appear?
The left-handed and right-handed chiralities of a vector-like fermion ψ
transform in the same way under the SM gauge groups SU (3)c × SU (2)L × U (1)Y
Vector-like quarks in many models of New Physics
Warped or universal extra-dimensions
KK excitations of bulk fields
Composite Higgs models
VLQ appear as excited resonances of the bounded states which form SM particles
Little Higgs models
partners of SM fermions in larger group representations which ensure the cancellation of
divergent loops
Gauged flavour group with low scale gauge flavour bosons
required to cancel anomalies in the gauged flavour symmetry
Non-minimal SUSY extensions
VLQs increase corrections to Higgs mass without affecting EWPT
SM and a vector-like quark
LM = −Mψ̄ψ
Gauge invariant mass term without the Higgs
SM and a vector-like quark
LM = −Mψ̄ψ
Gauge invariant mass term without the Higgs
Charged currents both in the left and right sector
ψL
ψR
W
ψL′
W
ψR′
SM and a vector-like quark
LM = −Mψ̄ψ
Gauge invariant mass term without the Higgs
Charged currents both in the left and right sector
ψL
ψR
W
ψL′
W
ψR′
They can mix with SM quarks
t′
×
ui
b′
×
di
Dangerous FCNCs −→ strong bounds on mixing parameters
BUT
Many open channels for production and decay of heavy fermions
Rich phenomenology to explore at LHC
Searches at the LHC
ATLAS (t′ )
1
800
0.8
750
0.6
0
0
700
0.4
650
0.2
600
1
BR(tZ)
0
1
BR(tH)
Observed T Quark Mass Limit [GeV]
CMS preliminary s = 8 TeV 19.6 fb-1
BR(bW)
BR(T → Ht)
CMS (t′ )
1
1
rb
en
mT = 400 GeV
Fo
rb
0.8
idd
0.6
en
mT = 450 GeV
Fo
rb
0.8
idd
0.6
0.4
ATLAS Preliminary
1
mT = 350 GeV
Fo
0.8
Status: Lepton-Photon 2013
idd
∫ L dt = 14.3 fb
-1
s = 8 TeV,
en
0.6
0.4
95% CL exp. excl.
95% CL obs. excl.
Ht+X
0.4
[ATLAS-CONF-2013-018 ]
Same-Sign [ ATLAS-CONF-2013-051]
0.2
0
0.2
0
0.2
0.4
0.6
0.8
1
1
0
0.2
0
0.2
0.4
0.6
0.8
1
1
rb
0.8
en
0.6
rb
en
0.6
0.4
0.2
0.2
0
0
0
0.4
0.6
0.8
1
1
Fo
0.2
0.4
Fo
en
0.6
0.8
1
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
0
[ATLAS-CONF-2013-056 ]
[ATLAS-CONF-2013-060 ]
SU(2) singlet
mT = 650 GeV
Fo
rb
idd
en
0.6
0.4
0.2
0
0.2
0.4
0.6
0.8
1
0
0
0.2
0.4
0.6
0.8
1
1
Fo
mT = 800 GeV
rb
Fo
en
mT = 850 GeV
rb
0.8
idd
idd
en
0.6
0.4
0.2
0
Zb/t+X
Wb+X
SU(2) (T,B) doub.
0.8
idd
0.4
0.2
0
1
en
0.6
0.4
0.2
rb
0.8
idd
en
0.6
0.4
0.8
1
mT = 750 GeV
rb
0.8
idd
0.6
mT = 600 GeV
1
mT = 700 GeV
rb
0.6
0
0
1
0.8
0.4
0.6
0.4
0.2
0.2
0.2
Fo
0.8
idd
0.4
0
0
mT = 550 GeV
Fo
0.8
idd
0
1
mT = 500 GeV
Fo
0.2
0
0.2
0.4
0.6
0.8
1
0
0
0.2
0.4
0.6
BR(T → Wb)
Bounds from pair production between 600 GeV and 800 GeV
depending on the decay channel
Common assumption: mixing with third generation only
0.8
1
Example: b′ pair production
P
b′
b
t
W−
W+
P
b̄′
t̄
W+
Common assumption
CC: b′ → tW
W−
Searches in the
same-sign dilepton channel
(possibly with b-tagging)
b̄
Example: b′ pair production
P
b
t
b′
W−
W+
P
b̄′
t̄
W+
Common assumption
CC: b′ → tW
W−
Searches in the
same-sign dilepton channel
(possibly with b-tagging)
b̄
If the b′ decays both into Wt and Wq
P
P
b′
b
t
W−
W+
b̄′
jet
W+
P
P
b′
jet
W−
W+
b̄′
jet
There can be less events in the same-sign dilepton channel!
Representations and lagrangian terms
Assumption: vector-like quarks couple with SM quarks through Yukawa interactions
Representations and lagrangian terms
Assumption: vector-like quarks couple with SM quarks through Yukawa interactions
SM
uc t d
s
b
SU(2)L
2 and 1
U (1)Y
qL = 1/6
uR = 2/3
dR = −1/3
LY
−yiu q̄iL Hc uiR
i,j
j
−yid q̄iL VCKM HdR
Singlets
(U)
(D)
Doublets
X
U U
D D
Y
1
2/3
2
-1/3
− λiu q̄iL Hc UR
− λid q̄iL HDR
7/6
1/6
Triplets
 
X
 
U
U
D 
D
Y
3
-5/6
− λiu ψL H (c) uiR
− λid ψL H (c) diR
2/3
-1/3
− λi q̄iL τ a H (c) ψRa
Representations and lagrangian terms
Assumption: vector-like quarks couple with SM quarks through Yukawa interactions
SM
uc t d
s
b
SU(2)L
2 and 1
U (1)Y
qL = 1/6
uR = 2/3
dR = −1/3
LY
yi v
2
i,j
j
yi v
− √d d̄iL VCKM dR
2
− √u ūiL uiR
Singlets
(t′ )
(b′ )
Doublets
X
t′ t′ b′ b′ Y
1
2/3
2
-1/3
i
− λ√u v ūiL UR
2
λi v
− √d d̄iL DR
2
7/6
1/6
 Triplets

X
 ′
 t′ 
t
 b′ 
b′
Y
3
-5/6
i
− λ√u v UL uiR
2
λi v
− √d DL diR
2
2/3
-1/3
λi v i
−√
ūL UR
2
− λi vd̄iL DR
Representations and lagrangian terms
Assumption: vector-like quarks couple with SM quarks through Yukawa interactions
SM
uc t d
s
b
SU(2)L
2 and 1
U (1)Y
qL = 1/6
uR = 2/3
dR = −1/3
LY
Lm
Free
parameters
yi v
2
i,j
j
yi v
− √d d̄iL VCKM dR
2
− √u ūiL uiR
Singlets
(t′ )
(b′ )
Doublets
X
t′ t′ b′ b′ Y
1
2/3
2
-1/3
i
− λ√u v ūiL UR
2
λi v
− √d d̄iL DR
2
7/6
1/6
 Triplets

X
 ′
 t′ 
t
 b′ 
b′
Y
3
-5/6
i
− λ√u v UL uiR
2
λi v
− √d DL diR
2
2/3
-1/3
λi v i
−√
ūL UR
2
− λi vd̄iL DR
−Mψ̄ψ (gauge invariant since vector-like)
4
M + 3 × λi
4 or 7
M + 3λiu + 3λid
4
M + 3 × λi
Outline
1
Motivations and Current Status
2
Couplings and constraints
3
Signatures at LHC
Couplings
Major consequences
Flavour changing neutral currents in the SM
Z
u
= u
t′
c
×
H
= uR
t′
×
c
H
uR
×
×
Z
cL
and flavour conserving neutral currents receive a contribution
cL
Couplings
Major consequences
Flavour changing neutral currents in the SM
Z
u
H
= u
t′
uR
×
×
Z
c
= uR
t′
×
c
×
H
cL
and flavour conserving neutral currents receive a contribution
Charged currents between right-handed SM quarks
W
uR
t′
× R bR′
W
= uR
×
dR
dR
and charged currents between left-handed SM quarks receive a contribution
cL
Couplings
Major consequences
Flavour changing neutral currents in the SM
Z
u
H
= u
t′
uR
×
×
Z
c
= uR
t′
×
c
×
H
cL
and flavour conserving neutral currents receive a contribution
Charged currents between right-handed SM quarks
W
uR
t′
× R bR′
W
= uR
×
dR
dR
and charged currents between left-handed SM quarks receive a contribution
All proportional to combinations of mixing parameters
cL
FCNC constraints
Rare top decays
u, c
u, c
W
t
b
t
b
b
W
Z
BR(t → Zq) = O(10−14 )
SM prediction
u, c
t
W
Z
Z
BR(t → Zq) < 0.24%
measured at CMS @ 5 fb−1
Meson mixing and decay
D0
c
W
di
u
D0
c
u
di
W
W
di
l+
νi
W
u
D̄0
c
l−
D0
c
Z
c
Z
u
D0
u
u
c
l+
l−
D̄0
Flavour conserving NC constraints
Zcc̄ and Zbb̄ couplings
q
c, b
q
Asymmetry parameters: Aq =
Z
q
q
Direct coupling measurements: gZL,ZR = (gZL,ZR )SM (1 + δgZL,ZR )
c, b
Decay ratios: Rq =
Γ (Z→qq̄)
Γ (Z→hadrons)
q
(gZL )2 −(gZR )2
q
q
(gZL )2 +(gZR )2
= ASM
q (1 + δAq )
= RSM
q (1 + δRq )
Atomic parity violation
u, d
Z
u, d
Weak charge of the nucleus
i
2c h
VL
QW = W (2Z + N )(guZL + guZR ) + (Z + 2N )(gdZL + gdZR ) = QSM
W + δQW
g
Most precise test in Cesium 133 Cs:
QW (133 Cs)|exp = −73.20 ± 0.35
QW (133 Cs)|SM = −73.15 ± 0.02
Constraints from EWPT and CKM
EW precision tests
t′
W
W
Contributions of new fermions
to S,T,U parameters
b′
CKM measurements
Modifications to CKM relevant for singlets and triplets because mixing in the left
sector is NOT suppressed
The CKM matrix is not unitary anymore
If BOTH t′ and b′ are present, a CKM for the right sector emerges
Higgs coupling with gluons/photons
Production and decay of Higgs at the LHC
g
γ
q
q
g
q
f
H
f
H
f
γ
New physics contributions mostly affect loops of heavy quarks t and q′ :
κgg = κγγ =
v
v
g +
g ′ ′ −1
mt htt̄ mq′ hq q̄
The couplings of t and q′ to the higgs boson are:
ghtt̄ =
mt
+ δghtt̄
v
ghq′ q̄′ =
mq ′
v
+ δghq′ q̄′
In the SM: κgg = κγγ = 0
The contribution of just one VL quark to the loops turns out to be negligibly small
Result confirmed by studies at NNLO
Outline
1
Motivations and Current Status
2
Couplings and constraints
3
Signatures at LHC
Production channels
Vector-like quarks can be produced
in the same way as SM quarks plus FCNCs channels
Pair production, dominated by QCD and sentitive to the q′ mass
independently of the representation the q′ belongs to
Single production, only EW contributions and sensitive to both
the q′ mass and its mixing parameters
Production channels
Pair vs single production, example with non-SM doublet (X5/3 t′ )
ΣHp b L
10
pair production
1
0.1
single X53
single t’
0.01
0.001
200
400
600
800
1000
m q,
pair production depends only on the mass of the new particle and
decreases faster than single production due to different PDF scaling
current bounds from LHC are around the region
where (model dependent) single production dominates
Decays
SM partners
Z
H
t′
t′
ui
ui
W+
W−
t′
Z
b′
t′
di
W−
b′
X5/3
di
H
b′
Neutral currents
di
W+
b′
ui
Charged currents
Y−4/3
Exotics
W+
W−
X5/3
Y−4/3
ui
, t′
Only Charged currents
di
, b′
Not all decays may be kinematically allowed
it depends on representations and mass differences
Decays of t′
Mixing ONLY with top
1.0
BR t ’
0.8
0.6
tH
0.4
tZ
0.2
bW
0.0
200
400
600
800
1000
m t’
Equivalence theorem at large masses: BR(qH ) ≃ BR(qZ)
Decays are in different channels (BR=100% hypothesis now relaxed in exp searches)
Decays of t′
Mixing ONLY with top
1.0
BR t ’
0.8
0.6
tH
0.4
tZ
0.2
bW
0.0
200
400
600
800
1000
m t’
Equivalence theorem at large masses: BR(qH ) ≃ BR(qZ)
Decays are in different channels (BR=100% hypothesis now relaxed in exp searches)
1
1
rb
mT = 400 GeV
Fo
rb
0.8
idd
ATLAS Preliminary
1
mT = 350 GeV
Fo
0.8
mT = 450 GeV
Fo
rb
0.8
idd
en
Status: Lepton-Photon 2013
idd
en
0.6
0.6
0.4
0.4
0.4
0.2
0.2
0.2
∫ L dt = 14.3 fb
-1
s = 8 TeV,
en
0.6
BR(B → Hb)
BR(T → Ht)
Still, current bounds assume mixing with third generation only!
95% CL exp. excl.
95% CL obs. excl.
Ht+X
[ATLAS-CONF-2013-018 ]
Same-Sign [ ATLAS-CONF-2013-051]
0
0
0.2
0.4
0.6
0.8
1
1
0
0
0.2
0.4
0.6
0.8
1
1
rb
0.2
0.4
0.6
0.8
rb
Wb+X
[ATLAS-CONF-2013-060 ]
rb
1
rb
mB = 450 GeV
Fo
rb
0.8
idd
Status: Lepton-Photon 2013
idd
en
0.6
0.4
0.4
0.2
0.2
0.2
0.4
0.6
0.8
1
0
0.2
0.4
0.6
0.8
1
1
rb
0
0.2
0.4
0.6
0.8
1
rb
mB = 600 GeV
Fo
rb
0.8
idd
en
0.6
0.6
0.6
0.4
0.4
0.4
0.4
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.4
0.6
0.8
1
0
0
0.2
0.4
0.6
0.8
1
1
Fo
0
en
0.2
0.4
0.6
0.8
1
Fo
0
en
0.2
0.4
0.6
0.8
1
Fo
0
en
0.2
0.4
0.6
0.8
1
Fo
0
en
0.2
0.4
0.6
0.8
1
Fo
0
en
0.2
0.4
0.6
0.8
1
Fo
en
0.6
0.6
0.6
0.6
0.6
0.4
0.4
0.4
0.4
0.4
0.4
0.2
0.2
0.4
0.6
0.8
1
0
0.2
0
0.2
0.4
0.6
0.8
1
0
0.2
0
0.2
0.4
0.6
0.8
1
0
0.2
0
0.2
0.4
0.6
BR(T → Wb)
0.8
1
0
0.2
0
0.2
0.4
0.6
0.8
1
0
0.2
0
0.2
0.4
0.6
0.8
1
0
0.6
0.8
1
mB = 850 GeV
idd
en
0.6
0.4
0
0.4
rb
en
0.6
0.4
0
0.2
Fo
0.8
idd
0.6
0.2
0
mB = 800 GeV
rb
0.8
idd
0
1
mB = 750 GeV
rb
0.8
idd
0
1
mB = 700 GeV
rb
0.8
idd
0
1
mT = 850 GeV
rb
0.8
idd
0
1
mT = 800 GeV
rb
0.8
idd
0
1
mT = 750 GeV
rb
0.8
idd
0
1
mT = 700 GeV
rb
idd
en
0.6
0.4
Fo
rb
en
0.6
0.4
0.2
SU(2) singlet
mB = 650 GeV
Fo
0.8
idd
en
0.6
0.4
0
[ATLAS-CONF-2013-056 ]
SU(2) (B,Y) doub.
1
mB = 550 GeV
Fo
0.8
idd
en
0
1
mB = 500 GeV
Fo
0.8
idd
0
0.6
1
95% CL obs. excl.
Same-Sign [ ATLAS-CONF-2013-051]
Zb/t+X
0
0.4
0
-1
95% CL exp. excl.
0.6
0.8
∫ L dt = 14.3 fb
s = 8 TeV,
en
0.6
0.2
1
rb
rb
en
0.4
mT = 650 GeV
Fo
en
mB = 400 GeV
Fo
0.8
idd
ATLAS Preliminary
1
mB = 350 GeV
Fo
0.6
SU(2) singlet
SU(2) (T,B) doub.
0.8
idd
en
1
0.8
0
1
mT = 600 GeV
Fo
0.8
idd
en
[ATLAS-CONF-2013-056 ]
1
mT = 550 GeV
Fo
0.8
idd
0
1
mT = 500 GeV
Fo
0.8
0
Zb/t+X
0.2
0
0.2
0.4
0.6
0.8
1
0
0
0.2
0.4
0.6
BR(B → Wt)
0.8
1
Decays of t′
Mixing ONLY with top
1.0
BR t ’
0.8
0.6
tH
0.4
tZ
0.2
bW
0.0
200
400
600
800
1000
m t’
Equivalence theorem at large masses: BR(qH ) ≃ BR(qZ)
Decays are in different channels (BR=100% hypothesis now relaxed in exp searches)
Still, current bounds assume mixing with third generation only!
Mixing with top and charm
Mixing ONLY with charm
1.0
bW
0.8
0.6
BR t ’
BR t ’
0.8
1.0
0.4
tH
0.2
cZ
cH
0.6
cZ
0.4
cH
tZ
0.0
200
400
600
m t’
800
1000
0.2
0.0
200
400
600
800
1000
m t’
Decay to lighter generations can be sizable
even if Yukawas are small!
Single Production
based on arXiv:1305.4172, accepted by Nucl.Phys.B
From couplings to BRs
Charged current of T (t′ )
g
4i
√ [T̄L/RWµ+ γ µ diL/R ]
L ⊃ κW VL/R
2
From couplings to BRs
Charged current of T (t′ )
g
4i
√ [T̄L/RWµ+ γ µ diL/R ]
L ⊃ κW VL/R
2
Partial Width
4i
2
|VL/R
|2
Γ (T → Wdi ) = κW
M3 g2 0
Γ (M, mW , mdi = 0)
64πm2W W
Assumption: massless SM quarks, corrections for decays into top (see 1305.4172)
From couplings to BRs
Charged current of T (t′ )
g
4i
√ [T̄L/RWµ+ γ µ diL/R ]
L ⊃ κW VL/R
2
Partial Width
4i
2
|VL/R
|2
Γ (T → Wdi ) = κW
M3 g2 0
Γ (M, mW , mdi = 0)
64πm2W W
Assumption: massless SM quarks, corrections for decays into top (see 1305.4172)
Branching Ratio
BR(T → Wdi ) =
4i |2
|VL/R
4j
∑3j=1 |VL/R |2
·
2 Γ0
κW
W
2 Γ0
∑V ′ =W,Z,H κV
′ V′
≡ ζi ξW
From couplings to BRs
Charged current of T (t′ )
g
4i
√ [T̄L/RWµ+ γ µ diL/R ]
L ⊃ κW VL/R
2
Partial Width
4i
2
|VL/R
|2
Γ (T → Wdi ) = κW
M3 g2 0
Γ (M, mW , mdi = 0)
64πm2W W
Assumption: massless SM quarks, corrections for decays into top (see 1305.4172)
Branching Ratio
BR(T → Wdi ) =
4i |2
|VL/R
4j
∑3j=1 |VL/R |2
·
2 Γ0
κW
W
2 Γ0
∑V ′ =W,Z,H κV
′ V′
≡ ζi ξW
Re-expressing the Lagrangian
L ⊃ κT
s
ζi ξW g
√ [T̄L/R Wµ+ γ µ diL/R ]
Γ0W
2
v
u 3
r
u
4i |2
with κT = t ∑ |VL/R
∑ κV2 Γ0V
i =1
V
The complete Lagrangian
T
ζi ξW
g
√ [T̄L Wµ+ γ µ diL ] +
Γ0W
2
s
ζ i ξ ZT g
[T̄L Zµ γ µ uiL ] −
Γ0Z 2cW
B
ζi ξW
g
√ [B̄L Wµ− γ µ uiL ] +
Γ0W
2
)
(s
ζi g
+ µ i
√
[
X̄
W
γ
u
]
+ κX
L
µ
L
Γ0W 2
(s
)
ζi g
√ [ȲL Wµ− γ µ diL ]
+ κY
0
ΓW 2
s
ζ i ξ ZB g
Γ0Z 2cW
L = κT
+ κB
(s
(s
s
T
ζi ξH
M
[T̄R HuiL ] −
Γ0H v
s
)
B
ζi ξH
M
i
[B̄L Zµ γ µ diL ] −
[
B̄
Hd
]
R
L
Γ0H v
s
T
ζ3 ξH
mt
[T̄L HtR ]
Γ0H v
+ h.c.
Model implemented and validated in Feynrules:
http://feynrules.irmp.ucl.ac.be/wiki/VLQ
3
∑ ζi = 1
i =1
∑
ξV = 1
V =W,Z,H
T and B: NC+CC, 4 parameters each (ζ 1,2 and ξ W,Z )
X and Y: only CC, 2 parameters each (ζ 1,2)
)
Cross sections (example with T)
In association with top
σ(T t̄) =
κT2
Tt̄
ξ Z ζ 3 σ̄Z3
3
+ ξW
∑
Tt̄
ζ i σ̄Wi
i =1
di
!
T
qi
t̄
q̄j
W
d̄j
Z
T
t̄
In association with light quark
3
σ(Tj) =
κT2
∑
ξW
i =1
Tjet
ζ i σ̄Wi
3
+ ξZ
∑
i =1
Tjet
ζ i σ̄Zi
qi
!
T
W, Z
qj
qj
qi
Z
T
q̄j
W
q̄k
In association with gauge or Higgs boson
3
σ(T {W, Z, H }) =
g
q
q
T
κT2
ξW
∑
ζ i σ̄iTW
3
+ ξZ
T
g
T
W, Z
q
W, Z
3
+ ξH
i =1
i =1
g
∑
ζ i σ̄iTZ
ui
∑
i =1
ui
T
ζ i σ̄iTH
!
g
T
T
H
ui
The σ̄ are model-independent coefficients: the model-dependency is factorised!
H
Cross sections
Coefficients (in fb) for T and T̄ with mass 600 GeV
with top
ζ1 = 1
ζ2 = 1
ζ3 = 1
Tt̄ +T̄t
σ̄Zi
Tt̄ +T̄t
σ̄Wi
12.6
1690
247
78.2
with light quark
Tj+T̄j
Tj+T̄j
σ̄Zi
σ̄Wi
69200
5380
-
51500
10700
4230
with gauge or Higgs
σ̄iTZ+T̄Z
σ̄iTH +T̄H
σ̄iTW +T̄W
5480
202
-
3610
133
-
2430
374
122
The cross section for pair production is 170 fb
Cross sections
Embed the model-dependency into a consistent framework
Benchmark 1
κ = 0.02
ζ 1 = ζ 2 = 1/3
Benchmark 2
κ = 0.07
ζ1 = 1
Benchmark 3
κ = 0.2
ζ2 = 1
Benchmark 4
κ = 0.3
ζ3 = 1
Benchmark 5
κ = 0.1
ζ 1 = ζ 3 = 1/2
Benchmark 6
κ = 0.3
ζ 2 = ζ 3 = 1/2
(1, 2/3)
T
15
464
564
399
495
834
(1, − 1/3)
B
14
455
457
167
-
-
(2, 1/6)
λd = 0
T
B
5.6
10
191
351
114
267
0.6
1.1
195
358
128
301
(2, 1/6)
λu = 0
T
B
9.5
3.7
272
103
451
190
398
166
-
-
(2, 1/6)
λd = λu
T
B
15
14
464
455
564
457
399
167
-
-
(2, 7/6)
X
T
15
5.6
528
191
272
114
1.2
0.6
538
195
307
128
(2, − 5/6)
B
Y
3.7
7.6
103
205
190
443
166
388
-
-
(3, 2/3)
X
T
B
30.5
15
7.4
1055
464
207
545
564
380
2.4
399
332
-
-
(3, − 1/3)
T
B
Y
5.6
7.1
7.6
191
227
205
114
228
443
0.6
84
388
-
-
Flavour bounds are necessary to get the inclusive cross sections
Flavour vs direct search
MadGraph, D-quark
MadGraph, X -quark
95% C.L. upper limits:
Observed
Expected
±1σ
±2σ
10
1
10-1
10-2
400
σ(pp → Qq) × BR(Q → Zq ) [pb]
σ(pp → Qq ) × BR(Q → Wq) [pb]
ATLAS search in the CC and NC channels
MadGraph, U -quark
95% C.L. upper limits:
Observed
Expected
±1σ
±2σ
10
1
10-1
s = 7 TeV
-1
∫ L dt = 4.64 fb
ATLAS
600
s = 7 TeV
800
∫ L dt = 4.64 fb
-1
10-2
Preliminary
1000
1200
1400
1600
1800
2000
mQ [GeV]
400
ATLAS
600
Preliminary
800
1000
1200
1400
1600
Assumptions: mixing only with 1st generation and coupling strength κ =
1800
2000
mQ [GeV]
v
MVL
Flavour vs direct search
Comparison with flavour bounds
Doublet HX TL
Triplet HX T BL
0.30
0.30
0.25
0.25
ATLAS NC
0.20
0.15
Κ
Κ
0.20
ATLAS NC
0.15
ATLAS CC
0.10
0.10
Flavour bound
Flavour bound
0.05
0.00
600
700
800
M@GeVD
ATLAS CC
0.05
900
1000
0.00
600
700
800
900
1000
M@GeVD
Assumptions: mixing only with 1st generation and coupling strength saturating flavour bounds
Flavour bounds are competitive with current direct searches
Conclusions and Outlook
After Higgs discovery, Vector-like quarks are a very promising playground for searches of
new physics
Fairly rich phenomenology at the LHC and many possibile channels to explore
→ Signatures of single and pair production of VL quarks are accessible at current CM energy and
luminosity and have been explored to some extent
→ Current bounds on masses around 600-800 GeV, but searches are not fully optimized for general
scenarios.
Model-independent studies can be performed for pair and single production, and also
to analyse scenarios with multiple vector-like quarks (work in progress, results very
soon!)