Post on 08-Feb-2021
Top Quark and Exotic Models: !Theoretical Overview
Qing-Hong Cao Peking University
7th International Workshop on Top Quark PhysicsOpt 2014
Oct. 02, 2014
TOP @ inSPIRE
0
100
200
300
400
500
600
1978198019821984198619881990199219941996199820002002200420062008201020122014
TheoryALL
Search for papers with ‘top’ in title
Two anomalies
2I will focus on the second anomaly and NP explanations
Top Quark and New Physics
Strongly Interacting
Higgs (125GeV)
Effective Field
Theory
Experimental Data
What could !we see?
What should we see?
Natural NP models always have non-trial couplings between top quark and
NP particles
SUSY, LH, Composite, RS, TC…
Weakly Interacting
3
Top quark as a probe of new physics
Gluino
Exotic Colored States
4th Gen
Vector Quark
FCNC
Charged Higgs
AFB
Extra Gauge Bosons
New Heavy Quarks
CPHeavy Quark Production via pQCD
TopColor Sextet
It appears often in the decay of NP resonances
4
Vector QuarksCommon in many NP models, Economics for model building
Mass Mixing and Heavy Quark Couplings to Higgs
!"#$%&'()(*+%,-.(/%01+23%4(+*5'6%7897:%;1($*1)1-.?%$-.1*+(+*5'%+*1%D"''$JE1%
BG,7/%'$-KE1.%
456$25,(
(
(
(
(
(
7&"+6$25,(
(
BC%L(5+@+% MNON%L(5+@+% PQDE$
Vector QuarksT ! W+b/Zt/Ht
B ! W+t/Zb/HbY ! W+tX ! W�b
bb̄, ⌧+⌧�, V V ⇤
``, jj
`⌫, jj W
Z
h
Y
T
B
X
t
b
b`⌫, bjj
Very Rich Collider Signatures6
Extra Color Gauge BosonSU(3)1 ⇥ SU(3)2 ! SU(3)C
SU(3)1 SU(3)2Model
qL tR bR (t, b)L qR
qLtR bR (t, b)LqR
New Axigluon
Classic Axigluon
Topgluon qL (t, b)L tR bRqR
q=u,d,c,s
dijet, AFB(t)
dijet, AFB(t)
dijet, FCNC
Frampton, Glashow (1987)
Frampton, Shu, Wang (2010)
Hill (1991)
+ Extra color scalars 7
Extra Weak Boson and Quarks
SMqL
uRdR
Heavy QuarkQL
QR
H
SU(3)C ⇥ SU(2)1 ⇥ SU(2)2 ⇥ U(1)X
SU(3)C ⇥ SU(2)L⇥U(1)L ⇥ U(1)X
SU(3)C ⇥ SU(3)W ⇥ U(1)XG(331) Model
U’(1) model Z-prime
G(221) Model
�
8
Extra Weak Gauge BosonsSU(2)1 SU(2)2 U(1)X
U(1)Y
U(1)em
⊗ ⊗SU(2)1 SU(2)2 U(1)X
SU(2)L
U(1)em
⊗ ⊗(a) (b)
U(1)Y SU(2)L
LRD (LRT): left-right doublet (triplet) model
LPD (LRT): Leptophobic doublet (triplet) model
HPD (LRT): Hadrophobic doublet (triplet) model
FPD (LRT): Fermio-phobic doublet (triplet) model
SQD: Sequential W’ with doublet Higgs
NUD: Non-universal doublet model
UUD: Un-unified doublet model
QHC, Li, Yu, Yuan
1205.3769
ken, Schmitz, Yu, Yuan
1003.3482
221 Model:SU(2)1 ⌦ SU(2)2 ⌦ U(1)X
9
Extra Weak Gauge Bosons221 Model:
q
q̄′
W ′
t
b̄
q
q̄
Z ′
t
t̄
L = q̄�µ(gZ0L PL + gZ0
R PR)q Z0µ ++q̄�
µ(gW0
L PL + gW 0
R PR)q0 W 0+µ + h.c.
TABLE I: Couplings of a W ′ to tb and a Z ′ to tt̄ for the sequential SM-like W ′/Z ′ (SSM)
model, the left-right symmetric model (LRM), and the top-flavor model, where sw (cw, tw) =
sin θw (cos θw, tan θw), θw is the weak mixing angle, g2 = e/sw is the weak coupling, αLR ≃ 1.6,
and sin φ̃ is taken to be 1/√2.
W ′tb Z ′tt̄
SSMg2√2b̄γµPLtW
′µ g26cw
t̄γµ((−3 + 4s2w)PL + 4s2wPR)tZ ′µ
LRMg2√2b̄γµPRtW
′µ g2tw6
t̄γµ(1
αLRPL + (
1
αLR− 3αLR)PR)tZ ′µ
Top-Flavorg2 sin φ̃√
2b̄γµPLtW
′µ g2 sin φ̃√2
t̄γµPLtZ′µ
• left-right symmetric model (LRM) [29]: Here, we consider a SU(2)L × SU(2)R ×
U(1)B−L model. The W ′ couplings to SM quarks are purely right-handed while the
Z ′ couplings are dominantly right-handed.
Table I is a summary of the couplings of a W ′ and a Z ′ to SM third generation quarks in
these models. The couplings to the quarks of first two generations are the same, except that
one should replace sin φ̃ by cos φ̃ in the top-flavor model.
A. Bounds on masses and couplings
The masses and couplings of Z ′ and W ′ bosons are bounded by various low energy
measurements (mainly via the four-fermion operators induced by exchanges of new heavy
gauge bosons) such as the precision measurements at the Z-pole at LEP-I [30], the W -
boson mass [30], the forward-backward asymmetry in bb̄ production at LEP-II [30], νe
scattering [31], atomic parity violation [32–34], Moller scattering [35], and so forth. The
bounds are severe when new gauge bosons couple to leptons directly, but they can be relaxed
for a leptophobic model, as analyzed in Ref. [22].
Tevatron data place a lower bound about 1.1 TeV on the mass of a W ′ [36] and about
1.07 TeV for a Z ′ [37], based on the charged lepton plus missing energy (ℓ±E̸T ) and µ+µ−
final states, respectively, with the assumption that the couplings between the W ′/Z ′ and the
SM fermions are the same as those in the SM. Searches for the W ′ and Z ′ at the Tevatron in
dijet events yield lower bounds on mW ′ and mZ′ , assuming SM couplings, of 840 GeV and
6
SU(2)1 ⌦ SU(2)2 ⌦ U(1)X
10
Extra Weak Gauge Bosons
0
@udD
1
A
0
@csS
1
A
0
@b�tT
1
A
3 3 3
SU(3)⇥ U(1)X �! SU(2)L ⇥ U(1)Y �! U(1)emH1 H2
Diaz, Martinez, Ochoa, hep-ph/0309280 Barreto, Coutinho, Sa Borges, 1103.1266 Buras, Fazio, Girrbach, Carlucci, 1211.1237
331 Model:
Z-prime: flavor changing coupling to u- and top-quark also the chiral coupling to light-quarks and top-quarks
SU(3)C ⌦ SU(3)W ⌦ U(1)X
11
Exotic Colored Scalars/VectorsEffective Lagrangian:
Atag, !Cakir, !
Sultansoy, !(1999)
Q = QL
U = uRD = dR
Arnold,!Pospelov,!
Trott,!Wise!
(2009)
12
Top Quark and New Physics
ProductionProton Proton
Others
t
Rare Decay or Light
Resonance not covered in this talk
tt
t
….
T,B,G0,W 0, Z 0,�0,�+,�8,�3,�6, DM 13
Single Top Quark Production
ProductionProton Proton
Others
t
….
14
Single Top Quark Productionb
g
t
WtW
u
d t
b
s-channel
Wu d
b tt-channel
W
u
d t
bW’ b
g
t
W
b’
FCNC Excited
quark
H+S6
New
resonance
Q2W > 0 Q2W < 0 Q
2W = m
2W
Drueke, Schwienhorst, Vignaroli, Walker, Yu, 1409.7607
u u
u/c tZ’ S0
QHC, Wudka, Yuan, 0704.2809Tait, Yuan, hep-ph/0007298
15
Single Top Quark Production(s-channel resonance and t-channel FCNC)
Drueke, Schwienhorst, Vignaroli Walker, Yu, 1409.7607
Tait, Yuan, hep-ph/0007298 Gogoladze et al, 1001.5260 16
Single Top Quark Production(s-channel excitation quark)
b
g
t
W
b’ q
g
t
Z
Q’q
g
t
g
Q’
Nutter, Schwienhorst, Walker, Yu, 1207.5179
L = gsB̄0�µB0 +gs�
2⇤Gµ⌫ b̄�
µ⌫�bLPL +
bRPR
�B0 + h.c.
L = gWp2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.L = gWp
2W+µ t̄�
µ(fLPL + fRPR)B0 + h.c.
17
Single Heavy Quark Productionq q0
bT
b
W
W⌫
`+
Little Higgs Perelstein, Peskin, Pierce hep-ph/0310039
Composite Higgs Li, Liu, Shu, 1306.5841
q
b
q0
Th
bb̄
t
Boosted jet-substructure
Reuter, Tonini, 1409.6962
18
Mono Top Quark Production(R-parity violating SUSY inspired)
Andrea, Fuks, Maltoni, 1106.6199 Wang, Li, Shao, Zhang, 1109.5963
W
d̄i
d̄j
φ
χ
tb
j
j
d̄i
d̄j
φ
χ
tb
v
l
W
FIG. 7: Feynman diagrams for the monotop production.
which are shown in Fig. 7. The symbol b and j denote a b-tagged jet and light quark
or gluon jet, respectively, and l refers to the first two generation charged leptons, i.e., e
and µ. We define the process with top hadronic decay as hadronic mode, while the one
with top semileptonic decay as semileptonic mode. The hadronic mode suffers from fewer
backgrounds in the SM than the semileptonic mode because of the smaller phase space due
to more particles in the final states. This mode has been studied in Ref. [11] where they
assume the branching fraction R(φ → tχ̄) equal to one. However, this assumption is over
optimistic. From Eq. (26) we get the branching fraction R(φ → tχ̄),
R(φ → tχ̄) =Γφ→tχ̄
Γφ→tχ̄ + Γφ→d̄s̄=
1
1 + z, (29)
with
z =8(λ12S )
2
|a3S|2m4φ
(m2φ −m2t −m2χ)λ1/2(m2φ, m2t , m2χ). (30)
Here we assume that the decay widths Γφ→uχ̄ = Γφ→cχ̄ = 0. In the case of λ12S = a3S =
0.2, mt = 173.1 GeV, mφ = 500 GeV and mχ = 50 GeV, we find Γφ→tχ̄ = 0.300 GeV,
Γφ→d̄s̄ = 3.183 GeV, and the branching fraction of φ → tχ̄ is just about 0.1. So, in this
work, we take into account the effect of both φ decay channels and below we will discuss
further the hadronic and leptonic modes in detail.
Before discussing the signal and backgrounds in detail, we first give some comments on
the parameter mχ. In the SUSY model, without the assumption of gaugino mass unification,
there is no general mass limit from e+e− colliders for the lightest neutralino [20]. The indirect
constraints from (g − 2)µ, b → sγ and B → µ+µ− show that the lightest neutralino mass
can be as low as about 6 GeV [36]. In our case, we choose the default value of mχ = 50 GeV
and discuss the effect on the discovery significance when varying mχ in the range 5 − 100
11
2
S
d̄j
d̄i
t
χ
t
g
ui
t
V
FIG. 1: Representative Feynman diagrams leading to mono-top signatures, through the resonant exchange of a coloredscalar field S (left) and via a flavor-changing interaction witha vector field V (right). In these two examples, the missingenergy is carried by the V and χ particles. More diagramswith, for example, t-channel and s-channel exchanges for thetwo type of processes respectively, are possible.
SU(3)c. As an example, consider the s-channel resonantcase
d̄id̄j → S or V → tχ ,
where dk denotes a down-type quark of generation k.Such processes occur in R-parity-violating SUSY [5]where, similarly to the case discussed in Ref. [6], the in-termediate particle is a (possibly on shell) squark andχ the lightest neutralino (d̄s̄ → ũi → tχ̃01, where ũi areany of the up squarks), or in SU(5) theories where a vec-tor leptoquark V decays into a top quark and a neutrino(d̄d̄ → V → tν̄). The key difference between these twoexamples is the mass of the invisible fermionic state in-ducing different transverse-momentum (pT ) spectrum forthe top quark. In the limit of a very heavy resonance,monotops can be seen as being produced through abaryon number-violating effective interaction (d̄s̄ → tχ̄),after having included the possible t- and u-channel ex-changes of a heavy field [7, 8]. Let us note that thefermionic particle could also be a Rarita-Schwinger field,as in SUSY theories containing a spin-3/2 gravitino field,or a multiparticle state (with a global half-integer spin),as in hylogenesis scenarios for dark matter [9].In the second class of models, the top quark is pro-
duced in association with a neutral bosonic state, eitherlong-lived or decaying invisibly, from quark-gluon initialstates undergoing a flavor-changing interaction, as dis-cussed, e.g., in Ref. [10]. Missing energy consists eitherin a two-fermion continuous state, as in R-parity conserv-ing SUSY [11], or in a spin-0 (S), spin-1 (V ) or spin-2(G) particle,
ug → ũiχ̃01 → tχ̃01χ̃01 , ug → tS , tV or tG .
EFFECTIVE THEORY FOR MONOTOPS
The top quark kinematic distributions depend bothon the partonic initial state and on the nature of theundetected recoiling object (scalar, massive or massless
fermion, vector or tensor), as well as on the possiblepresence of an intermediate resonant state. This sug-gests a model-independent analysis where we account forall cases within a single simplified theory, in the samespirit as Ref. [12]. Assuming QCD interactions to beflavor-conserving, as in the SM, the flavor-changing neu-tral interactions are coming from the weak sector. Wedenote by φ, χ and V the possible scalar, fermionic andvectorial missing energy particles, respectively and by ϕand X scalar and vector fields lying in the fundamen-tal representation of SU(3)c which could lead to res-onant monotop production.1 In addition, we obtain asimplified modeling of four-fermion interactions throughpossible s, t, u exchanges of heavy scalar fields ϕ and ϕ̃.The corresponding effective Lagrangian in terms of masseigenstates reads
L = LSM
+ φū[
a0FC+b0
FCγ5]
u+Vµū[
a1FCγµ+b1FCγ
µγ5]
u
+ϵijkϕid̄cj
[
aqSR+bqSRγ5
]
dk+ϕiūi[
a1/2SR+b1/2SRγ5
]
χ
+ϵijkϕ̃id̄cj
[
ãqSR+ b̃qSRγ5
]
uk+ϕ̃id̄i[
ã1/2SR+ b̃1/2SRγ5
]
χ
+ ϵijkXµ,i d̄cj
[
aqV Rγµ + bqV Rγ
µγ5]
dk
+Xµ,i ūi[
a1/2V Rγµ + b1/2V Rγ
µγ5]
χ+ h.c.,
(1)
where the superscript c stands for charge conjugation,i, j, k are color indices in the fundamental representationand flavor indices are understood. The matrices (in fla-
vor space) a{0,1}FC and b{0,1}FC contain quark interactions
with the bosonic missing-energy particles φ and V , while
a1/2{S,V }R and b1/2{S,V }R are the interactions between up-type
quarks, the invisible fermion χ and the new colored statesϕ and X . The latter also couple to down-type quarkswith a strength given by aq{S,V }R and b
q{S,V }R. Because
of the symmetry properties of the ϵijk tensor, identicalquark couplings to the scalar field ϕ vanish and so dotheir axial couplings to the vector field X . In the caseof four-fermion interactions, we also need to introduce
additional ãqSR, b̃qSR, ã
1/2SR and b̃
1/2SR interaction matrices,
assuming heavy masses for the ϕ and ϕ̃ fields.
1 For simplicity, we neglect spin-2 gravitons, as their flavor-changing couplings are loop-induced and thus very small [13],as well as any of their excitations, which, even if they have, onthe one hand, typically flavor-violating couplings at tree level, donot lead, on the other hand, to a missing energy signature. Onthe same footing, we do not consider spin-3/2 fields since theircouplings are, at least in SUSY theories, in general suppressedby the SUSY-breaking scale.
5
10
15
20
2530
0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.140.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
ΛS12
a S3
FIG. 11: The significance in the hadronic mode at the LHC (√s = 7 TeV) with an integrated
luminosity of 1 fb−1 versus the parameters λ12S and a3S , assumingmφ = 500 GeV and mχ = 50 GeV.
LHC 7 TeV S! B "5
1 fb#1
10 fb#1
600 800 1000 1200 1400 1600 1800 20000
1
2
3
4
5
mΦ!GeV
ΛS
FIG. 12: The 5σ discovery limits of mφ and λS(= λ12S = a3S) in the hadronic mode at the LHC
(√s = 7 TeV). Either band consists of twenty solid lines from the bottom up corresponding to the
value of mχ varying from 5 GeV to 100 GeV with a step of 5 GeV.
B. Semileptonic mode
For the semileptonic mode, the dominant backgrounds are pp → W (lν)j with the jet
misidentified as a b-jet and single top production with semileptonic top quark decay. The
Wj background is very large because there are only two final-state particles, compared with
17
see Theveneaux-Pelzer’s poster
19
Top-Antitop or Top-Top ! Quark Pair Production
ProductionProton Proton
Others
t
t
20
Top-quark F-B asymmetry in the SM(A charge asymmetry arises at NLO)
VOLUME 81, NUMBER 1 P HY S I CA L REV I EW LE T T ER S 6 JULY 1998
Charge Asymmetry in Hadroproduction of Heavy Quarks
J. H. Kühn and G. RodrigoInstitut für Theoretische Teilchenphysik, Universität Karlsruhe, D-76128 Karlsruhe, Germany
(Received 12 February 1998; revised manuscript received 17 April 1998)A sizable difference in the differential production cross section of top and antitop quarks, respectively,
is predicted for hadronically produced heavy quarks. It is of order as
and arises from the interferencebetween charge odd and even amplitudes, respectively. For the Fermilab Tevatron it amounts to upto 15% for the differential distribution in suitable chosen kinematical regions. The resulting integratedforward-backward asymmetry of 4% 5% could be measured in the next round of experiments. Atthe CERN Large Hadron Collider the asymmetry can be studied by selecting appropriately chosenkinematical regions. [S0031-9007(98)06481-3]
PACS numbers: 12.38.Qk, 12.38.Bx, 13.87.Ce, 14.65.Ha
Top quark production at hadron colliders has becomeone of the central issues of theoretical [1] and experimen-tal [2] research. The investigation and understanding ofthe production mechanism is crucial for the determina-tion of the top quark couplings, its mass, and the searchfor new physics involving the top system. A lot of efforthas been invested in the prediction of the total cross sec-tion and, more recently, of inclusive transverse momen-tum distributions [1].In this Letter we will point to a different aspect of the
hadronic production process, which can be studied witha fairly modest sample of quarks. Top quarks producedthrough light quark-antiquark annihilation will exhibita sizable charge asymmetry—an excess of top versusantitop quarks in specific kinematic regions—inducedthrough the interference of the final state with initial-state radiation [Figs. 1(a) and 1(b)] and the interferenceof the box with the lowest-order diagram [Figs. 1(c)and 1(d)]. The asymmetry is thus of order a
s
relativeto the dominant production process. In suitable chosenkinematical regions it reaches up to 15%, the integratedforward-backward asymmetry amounts to 4%–5%. Topquarks are tagged through their decay t ! b W1 and canthus be distinguished experimentally from antitop quarksthrough the sign of the lepton in the semileptonic modeand eventually also through the b tag. A sample of 100to 200 tagged top quarks should, in fact, be sufficient fora first indication of the effect.Top production at the Fermilab Tevatron is dominated
by quark-antiquark annihilation, hence the charge asym-metry will be reflected not only in the partonic rest framebut also in the center of mass system of proton and an-tiproton. The situation is more intricate for proton-protoncollisions at the CERN Large Hadron Collider (LHC),where no preferred direction is at hand in the laboratoryframe. Nevertheless, it is also in this case possible topick kinematical configurations which allow the study ofthe charge asymmetry.The charge asymmetry has also been investigated in
[3] for a top mass of 45 GeV. There, however, only
the contribution from real gluon emission was consideredrequiring the introduction of a physical cutoff on thegluon energy and rapidity to avoid infrared and collinearsingularities. Experimentally, however, only inclusivetop-antitop production has been studied to date, and theseparation of an additional soft gluon will in general bedifficult. In this Letter, we will therefore include virtualcorrections and consider inclusive distributions only. Wewill see below that the sign of the asymmetry for inclusiveproduction is opposite to the one given for the t¯tg processin [3]. The charge asymmetry of heavy flavor productionin quark-antiquark annihilation to bottom quarks was alsodiscussed in [4–6] where its contribution to the forward-backward asymmetry in proton-antiproton collisions wasshown to be very small. In addition, there is also a slightdifference between the distribution of top and antitopquarks in the reaction gq ! t¯tq. At the Tevatron itscontribution is below 1024. (This effect should not beconfused with the large asymmetry in the top quarks’angular or rapidity distribution in this reaction which is atrivial consequence of the asymmetric partonic initial stateand vanishes after summing over the incoming partonbeams.)
(c) (d)
(b)(a)
q
q
Q
Q
FIG. 1. Origin of the QCD charge asymmetry in hadroproduc-tion of heavy quarks: interference of final-state (a) with initial-state (b) gluon bremsstrahlung plus interference of the box (c)with the Born diagram (d).
0031-9007y98y81(1)y49(4)$15.00 © 1998 The American Physical Society 49
t̄
t
P (q) P̄ (q̄)
21
Kuhn, Rodrigo
hep-ph/9802268
SM NLO QCD
AtFB = 5%
Brown, Ellis, Rainwater
hep-ph/0509267
Collider simulation of tt+0(1)j
Measuring AFB is
very challenging
Almeida, Sterman, Vogalsang
0805.1885
NLL Threshold resum.
Asymmetry is robust
Dittmaier, Uwer, Weinzierl
hep-ph/0703120
NLO QCD corr. to ttbar+j
Ahrens, Ferroglia, Neubert,
Pecjak, Li Lin Yang,
1003.5827
SCET NNLL
1998 2005 2007 2008 2010
Melnikov, Schulze
1004.3284
Confirm Dittmaier et al
D0 (1.9 fb-1)
0712.0851
uncorrected
2011
AFB = [12± 8± 1]%
CDF (1.9 fb-1)
0806.2472
!Consistent with SMAFB = [24± 14]%
D0 (5.4fb-1)
1107.4995
CDF (5.3fb-1)
1101.0034
AFB = 0.475± 0.114mtt̄ � 450 GeVfor
AtFB = [19.6± 6.5]%A`FB = [15.2± 4.0]%
SM t
heo.
Pre
dict
ion
Exp. Measurements
Timeline of top-quark AFB
22
Top Quark AFB and NPs-channel t-channel (Flavor changing)
Effective theory q
q
t
t
q
q
q
q
t
t
t
t
Z 0,W 0,�
�6,�3̄
q
q
t
t
q
q
t
t
g
G0
SM
23
Timeline of and NP modelsAtFB
2007, 2008 2010, 20112009
Antunan, Kuhn, Rodrigo
Axigluon
0709.1652
Frampton, Shu, Wang
Axigluon
0911.2955
Shu, Tait, Wang
Color Sextet/triplet scalar
0911.3237
Arhrib, Benbrik, Chen
Color Sextet/triplet scalar
0911.4875
Djouadi, Moreau, Richard, singh
KK Gluon
0906.0604
Jung, Murayama, Pierce, Wells
FCNC Z-prime
0907.4112
Cheung, Keung, Yuan
FC W-prime
0908.2589
J. Cao, Heng, Wu, Yang
-SUSY and TC2
0912.14476R
QHC et al
Effective coupling
(G’, Z’, W’, H0,H+)
1003.3461
Jung, Ko, Lee, Nam
EFT
0912.1105
Ferrario, Rodrigo
Axigluon
0809.3353
Ferrario, Rodrigo
chiral G’
0906.5541
Xiao, Wang, Zhu,
NLO QCD to Z-prime
1006.2510
Shao, Li, et al
NLO QCD to EFT
1107.4012Yan, Wang, Shao, Li
NLO QCD to W-prime
1110.6684
s-channel
t-channel
EFT
NLO
QC
D
Dorsner, Fajfer,Kamenik, Kosnik,
Colored scalar
0912.0972
Bauer et al,
NLO RS
1008.0742
Chivukula, Simmons, Yuan
Axigluon
1007.0260
Aguilar-Saavedra
Perez-Victoria
1103.2765
Degrande, Gerard,
Grojean, Maltoni,
Servant, 1010.6304
24
See review: kamenik, Shu, Zupan, 1107.5257 Aguilar-Saavedra, Amidei, Juste, Perez-Victoria,1406.1798 25
1) Same Sign Top Quark Pairs-channel t-channel
Mohapatra, Okada, Hai-Bo Yu, 0709.1486 Berger, QHC, Chen, Shaughnessy, Zhang, 1005.2622, 1009.5379 Aguilar-Saavedra, Perez-Victoria, 1104.1385 Atwood, Gupta, Soni, 1301.2250
Maximal flavor violation Bar-Shalom, Rajaraman, Whiteson, Yu, 0803.3795FCNC effective coupling see Goldouzian’s talk, 1408.0493
3⌦ 3 = 6� 3̄u
u
tL
tL
(tR)
(tR)�(3,1)6,3
u
uZ 0
tR
tR
Flavor changing Z-prime Berger, QHC, Chen, Li, Zhang 1101.5625
�
26
2) Top Quark Pair Plus one Jet(Flavor Changing Interaction)
Gresham, Kim, Zurek, 1102.0018
g
u
t
u(t)
t̄(ū)
Z 0
g t
d W0
t̄
d
Berger, QHC, Chen, Li, Zhang, 1101.5625
g
u
t̄
t
u
�6,3
27
3) Top Quark Pair Plus One Jet(Third Generation Favored W-prime and Z-prime)
Topflavor Seesaw Model He, Tait, Yuan (2000), Wang, Du, He (2013)
g
t
Z 0
t̄
g t
W 0t̄
bb
Berger, Cao, Yu, Yuan, 1108.3613
b
b
28
4) Top Quark Pair Plus One Jet(Charged Higgs Boson)
b
g
t
t̄
b
H�
X-section is large for large tanb in MSSM or Type II 2HDB.
X-section depends on mH and tanb
Top-quark polarization depends on tanb
βtan0 5 10 15 20 25 30 35 40
decay
D
-1
-0.5
0
0.5
1
decayDFB2A
=400GeV-H=14TeV, Ms,-tH
(a)
βtan0 5 10 15 20 25 30 35 40
decay
D-1
-0.5
0
0.5
1
decayDFB2A
=400GeV-H=14TeV, Ms(b)
FIG. 12: (a) The degree of polarization of the antitop quark as a function of tan β of the tH−
signal event and (b) of all the signal and background processes with mH± = 400 GeV. The solid
black curve shows the degree of polarization defined in Eq. (37); the dashed red curve shows 2AFB.
The green band in (b) represents only the statistical uncertainties.
tan β has been considered very hard to measure. Figure 12 shows that the Ddecay varies
rapidly in the region of tan β = 5 ∼ 10. This feature enables us to determine tan β using
top polarization. However, the degree of polarization cannot be used to determine the value
of tan β in the large tanβ region as the degree of polarization approaches -1. Including the
t̄H+ signal and the two SM backgrounds inevitably reduces the degree of polarization, as
depicted in Fig. 12(b). The green band [cf. Eq. (39)] shows the statistical uncertainties
derived from all the signal and background events after all the kinematic cuts and event
reconstructions.
V. CONCLUSION AND DISCUSSION
The charged Higgs boson, an undoubted signal of new physics, appears in many new
physics models. In the type-II two-Higgs-doublet model the chirality structure of the cou-
pling of charged Higgs boson to the top and bottom quarks is very sensitive to the value
of tan β. As the polarization of the top quark can be measured experimentally from the
top quark decay products, one could make use of the top quark polarization to determine
the value of tan β. In this work we preform a detailed analysis of measuring top quark
polarization in the charged Higgs boson production channels gb → tH− and gb̄ → t̄H+. We
calculate the helicity amplitudes of the charged Higgs boson production and decay. Our
calculation shows that the top quark from the charged Higgs boson decay provides a good
19
QHC, Wan, Wang, Zhu, 1301.6608
Ddecay ⇠(mt cot�)2 � (mb tan�)2)(mt cot�)2 + (mb tan�)2)
Huitu, Rai, Rao, Rindani, Sharma, 1012.0527 Godbole, Hartgring, Niessen, White, 1111.0759 Gong, Si, Yang, Zheng,1210.7822
29
-
5) Top Quark Pair Plus JetsHeavy Quark Pair Production
Color Sextet/Triplet Scalar Pair Production
g
g
t
t̄
T/B
T̄ /B̄
Z/W
g
g
T
T̄
t
t̄
h
h
g
g
t
t̄
�6,3
�6,3
b
b̄
(Faked Top Quark Pair)
g
g
T
T̄
b
b̄
W
W
30
6) Top Quark Pair + Invisibles
Top-Quark Mediated Dark Matter Models
Dark Matter Effective Theory: Cheung, Mawatari, Senaha, Tseng, Yuan, 1009.0618 Gomez, Jackson, Shaughnessy, 1404.1918
g
g
t̃
˜̄t
t
t̄
χ̃0
χ̃0
g
g
T−
T−
t
t̄
AH
AH
SUSY LHT, UED
UV Completion Theory: Jackson, Servant, Shaughnessy, Tait, Taoso,1303.4717 31
t
Triple Top Quark Production
ProductionProton Proton
Others
t
tFCNC process
u,c g
Same-sign lepton pair32
Triple Top Quark Production
Topcolor-assisted technicolor model with large FCNC top-coupling to explain AFB(t)
Cui, Han, Schwartz (2011) Han, Liu, Wu, Yang (2012)
Chuan-Ren Chen (2014)
Barger, Keung, Yencho, 1001.0211
Leptophobic Z’ from U’(1) directly couples top-quark to u-quark to explain AFB(t)
g
u t
tt
Z 0
33
t
Four Top Quark!Production
ProductionProton Proton
Others
t
tt
34
Four Top Quark Productiont
t̄
t̄
tG0
t
t̄
t̄
t�8
t
t̄t̄
tt
t̄t̄
t
t
t̄
t̄
t�6
⇢⇡
Axigluon!KK Gluon
Color Octet!Scalar
Color Sextet!Scalar
TC2 Top Compositeness
Aguilar-Saavedra,!Santiago (2012)
Lillie, Shu, Tait (2007)
Chen, Klemm, Rentala, Wang!(2008)
SM QCD production @ NLO, ! Bevilacqua and Worek, 1206.3064 See Keaveney’s poster
Han, Liu, Wu, Yang (2012)Kumar, Tait, Veg-Morale (2009)
Plehn, Tait (2008)
35
t
Six or More Top Quark! Production
ProductionProton Proton
Others
t
tt
t36
Six or More Top Quark ProductionDeandrea, Deutschmann, 1405.6119
Color quantum #
37
Summary
38
Top quark as a probe of new physics
Gluino
Exotic Colored States
4th Gen
Vector Quark
FCNC
Charged Higgs
AFB
Extra Gauge Bosons
New Heavy Quarks
CPHeavy Quark Production via pQCD
TopColor Sextet
It appears often in the decay of NP resonances
39
Top Quark Production: rich signatures
Top
Single Top Top Pair
Triple TopsFour Tops40Flavor changing+Flavor conserving
Top Quark Production: rich signatures
Top
Single Top
u
d t
bW’H+S6
u u
u/c tZ’ S0
b
g
t
W
b’
Top Pair
Triple TopsFour Tops40Flavor changing+Flavor conserving
Top Quark Production: rich signatures
Top
Single Top
u
d t
bW’H+S6
u u
u/c tZ’ S0
b
g
t
W
b’
Top Pair
Triple TopsFour Tops
�(3,1)6,3u
u
t
tg t
W 0t̄
bb
g
g
T
T̄
t
t̄
h
h
g
g
T−
T−
t
t̄
AH
AH
40Flavor changing+Flavor conserving
Top Quark Production: rich signatures
Top
Single Top
u
d t
bW’H+S6
u u
u/c tZ’ S0
b
g
t
W
b’
Top Pair
Triple TopsFour Tops
�(3,1)6,3u
u
t
tg t
W 0t̄
bb
g
g
T
T̄
t
t̄
h
h
g
g
T−
T−
t
t̄
AH
AH
gtt
Z 0tu
40Flavor changing+Flavor conserving
Top Quark Production: rich signatures
Top
Single Top
u
d t
bW’H+S6
u u
u/c tZ’ S0
b
g
t
W
b’
Top Pair
Triple TopsFour Tops
t
t̄t̄
t
t
t̄
t̄
tG0
�(3,1)6,3u
u
t
tg t
W 0t̄
bb
g
g
T
T̄
t
t̄
h
h
g
g
T−
T−
t
t̄
AH
AH
gtt
Z 0tu
40Flavor changing+Flavor conserving