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Fr -top e ve n ts a t LHC f rom top- i li c n ew ys ics · 2018. 11. 1. · F!r -top e ve n ts a t...
28
F!r-top events at " LHC from top-ilic new ysics Géraldine SERVANT, CERN-TH ● Léa Gauthier, Anne-Isabelle Etienvre (ATLAS, SPP, CEA Saclay ) paper in preparation, for a short preview see chapter 12, p.137 of 1005.1229 in collaboration with
Transcript of Fr -top e ve n ts a t LHC f rom top- i li c n ew ys ics · 2018. 11. 1. · F!r -top e ve n ts a t...
F!r-top events at " LHC
from top-philic new physicsGéraldine SERVANT, CERN-TH
● Léa Gauthier, Anne-Isabelle Etienvre (ATLAS, SPP, CEA Saclay )
paper in preparation, for a short preview see chapter 12, p.137 of 1005.1229
in collaboration with
Four-top production in the Standard Model
t
t
t
t
q
qt
t
t
t
g
g
+ + ....
σLHC ~ 7.5 fb @ 14 TeV
➾ 4 top final state sensitive to several classes of new TeV scale physics
88 %
σLHC ~ 0.2 fb @ 7 TeV
e.g. SUSY (gluino pair production with g → t t χ0)~ -
top compositeness
t
tg
g
t
tX
Low energy effective theory approach
After integrating out heavy resonances, we are left with higher dimensional operators such as
1Λ2
(tRγµtR)(tRγµtR)
leading to:
In particular, well-motivated models where new heavy resonances have a preference for the top quark
[Pomarol-Serra,’08] [Lillie-Shu-Tait,’08]
t t - ν
ν -or
-t
t Z’
gg → tt + Z ′
tt + ET
tttt
Z′ →
νν
Z ′→tt
Z’ has suppressed couplings to light quarks -> no observable resonances
Four-top events from a top-philic and Dark Matter-philic Z’
instead:
Jackson, Servant, Shaughnessy,Tait, Taoso,’09
(DM)(DM)
t t-
4-top production cross sections at the LHC
7 Study of an effective interaction
7.1 A few about theory
In low energy effective theory approch, after integrating out heavy resonances, we are left with higherdimensional operators such as :
1
Λ2(t̄RγµtR)(t̄RγµtR) (11)
leading to :
Fig. 74 – Feynman diagram of the process
7.2 Study of the process
7.2.1 cross section
On the figure ?? is represented the cross section of this process versus Λ for 14TeV in the center ofmass and a renormalisation and factorisation scale of 2mtop.
[GeV]!0 200 400 600 800 1000 1200 1400 1600
Cro
ss s
ecti
on
[fb
]
1
10
210
310
410
510
Cross section versus lambda for the effective interaction
(a)
[GeV]!, KK
, MZ’M400 600 800 1000 1200 1400 1600
Cro
ss s
ecti
on
[fb
]
-310
-210
-110
1
model KK
g
Z’ model
effective interaction
SM
=14TeVs for tt tt"pp
(b)
Fig. 75 – cross section of the effective interaction versus Λ for√
s = 14TeV and µ = µF = µR = 2mtop
(a) and superposition of this signal with the Kaluza Zlein model, the Z’ model and the SM (b)
7.2.2 polarisation
On the figure ?? is represented the value of the polarisation of the top (value of the parameter A inthe formula 7). These values are for the distribution of cos(θl+).
47
[pb]
(gZ′
tR= 3)
ννq̄ ql+ l+ ν l+
B
B̄
t
t̄
W+
W−W+
W−
l+qq̄
b
b̄
T5/3
T̄5/3
W+W+
ν qq̄ qq̄
t
t̄
b
b̄W−
W−
same-sign dilepton channel powerful to get rid of the ttbar bgd
[Contino & Servant, ‘08]promising to search for WW final states from pair
production of heavy quarks (recently used by CDF to put bound on mass of 4th generation b’)
tttt production: similar final state but 2 additional b quarks- -
final state: l± l± + n jets + ET,missing
(of which 4 are b-jets)
t t-
t
t
t
t−
−Z’
t
t
t
t
−
−
Z’
Four-top events from a top-philic Z’
Higgs profile
!
BulkUVbrane
IRbrane
!light" SM fields live here
SM sector Composite sector
UV brane Bulk + IR brane
ds2 = e−2kydxµdxνηµν − dy2
RH top
is here
L = LSM − 14F ′
µνF ′µν + M2Z′Z ′
µZ ′µ + iν̄γµDµν + gtRt̄γµPRZ ′µt +
χ
2F ′
µνFµνY
Dµ ≡ ∂µ − i (gνRPR + gν
LPL) Z ′µ
A very simple effective theory
There is a new spontaneously broken U(1)’.The only SM particle with a large coupling to the Z’ is the top quark
This model is inspired by the Randall-Sundrum setup (warped extra dimension):
More generally, in models of partial fermion compositeness, natural to expect that only the top couples sizably to a new strongly interacting sector.
TeV KK modes (such as Z’) have enhanced couplings
to RH top quark
DM
Jackson, Servant, Shaughnessy,Tait, Taoso,’09 Agashe-Servant ’04; Belanger-Pukhov-Servant ’07
(as well as Higgs and DM)
Yukawa hierarchy comes from the hierarchy of compositeness
Partial compositeness: Dual picture
zero mode mass eigen state is mixture of elementary and composite
Higgs is part of composite sector: it couples only to composite fermions
massless
SM sectorstrong sectorEWSBelementary fermions: χ
Higgsheavy fermions: ψ
vector resonances: ρ
linear mixing
massive
amount of compositeness in the light dof
|light >L= cos φ|χL > +sinφ|ψL >|heavy >L= − sinφ|χL > +cos φ|ψL >
|heavy >R= |ψR >
−∆χLψR
tanφ =∆M∗
pp->ttZ’->tttt production cross section-- -
!
Gauthier L – Servant G – Etienvre A.I GDR Terascale 31 mars 2010 6
Cross section of the process
We work with √s = 14 TeV
We have : = 838 fb for m(Z') = 500GeV!
= 61 fb for m(Z')= 1 TeV!
If we work with √s = 7TeV = 110 fb for m(Z') = 400GeV!
!"#
$%&'
()*+
mass of Z’ [GeV]200 400 600 800 1000 1200 1400 1600 1800 2000
Cros
s se
ctio
n [p
b]
-410
-310
-210
-110
1
= 14 TeV s = 10 TeVs = 7 TeVs
SM 14 TeVSM 10 TeVSM 7 TeV
tt for pp->ttZ’Cross section versus M
(gZ′
tR= 3)
) [GeV]tM(t400 600 800 1000 1200 1400 1600 1800
]-1
[GeV
)tdM
(t !d
!1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
) [GeV]tM(t400 600 800 1000 1200 1400 1600 1800
]-1
[GeV
)tdM
(t !d
!1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
)tdistribution of M(t from the Z’ for M(Z’)=1.2TeVtt
for M(Z’)=1.2TeVtspectator t
random combination for M(Z’)=1.2TeV
SM
= 500GeV"effective model for
t t invariant mass-
for 14TeV in the COM. We can see that the maximum of the distribution for the random combinationdepends on the mass of the Z’. So we plot this maximum versus the mass of the Z’.
mass of Z’ [GeV]400 600 800 1000 1200 1400 1600
)tm
axim
um
of
M(t
400
500
600
700
800
900
1000 / ndf 2! 0.2768 / 5
origine 74.97± 306.5 slope 0.1187± 0.3794
/ ndf 2! 0.2768 / 5origine 74.97± 306.5 slope 0.1187± 0.3794
)versus m(Z’)tmaximum of M(t
Fig. 19 – distribution of the maximum of the distribution M(tt̄) for a random combination versus themass of the Z’
Thanks to a fit on the figure 19 we find this dependance is linear and the parameters are :– origin of the curve : 306.5 ± 74.97– slope of the curve : 0.379 ± 0.12
3.3.3 Angle between the quarks
)"cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
)"cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
angle between the top and antitop
Z’=350GeV
tspectator tZ’=1500GeV
tspectator tSM
(a)
)"cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
)"cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
angle between the top and antitop for M(Z’)=800GeV
no cut on the Z’800GeV<M(Z’)<1000GeV
900GeV<M(Z’)<1100GeV
no cut for the SM
)<1000GeVt800GeV<M(t
)<1100GeVt900GeV<M(t
(b)
Fig. 20 – distribution of the angle between the top and antitop quarks from the Z’, for the spectator tt̄and for the SM (a) and distribution of this angle for different cuts if M(Z’)=800GeV (b)
For low Z’ masses the quarks are emitted with low angles due to small values of the transverse momen-tum and for higher masses it is the contrary. For the SM we take the random combination. For this figurethe curves are normalized to 1.
14
for random combination
) [GeV]tM(t400 600 800 1000 1200 1400 1600
Num
ber o
f eve
nts/
(12G
eV)
-210
-110
1
10
210
) [GeV]tM(t400 600 800 1000 1200 1400 1600
Num
ber o
f eve
nts/
(12G
eV)
-210
-110
1
10
210
=14TeVs and -1L=200pbMz’=350 GeVMz’=500 GeVMz’=800 GeVMz’=1200 GeVSM
3.3.2 Study of the invariant mass Mtt̄
) [GeV]tM(t
400 600 800 1000 1200 1400 1600
Nu
mb
er
of
even
ts/(
12
GeV
)
-210
-110
1
10
210
) [GeV]tM(t
400 600 800 1000 1200 1400 1600
Nu
mb
er
of
even
ts/(
12
GeV
)
-210
-110
1
10
210
=14TeVs and -1L=200pb
Mz’=350 GeV
Mz’=500 GeV
Mz’=800 GeV
Mz’=1200 GeV
SM
(a)
[GeV]T
with the highest pt for the t and tt
M
500 1000 1500 2000 2500
Nu
mb
er
of
eve
nts
/(12
Ge
V)
-210
-110
1
10
[GeV]T
with the highest pt for the t and tt
M
500 1000 1500 2000 2500
Nu
mb
er
of
eve
nts
/(12
Ge
V)
-210
-110
1
10
=14TeVs and -1L=200pb
Mz’=350 GeV
Mz’=500 GeV
Mz’=800 GeV
Mz’=1200 GeV
SM
(b)
Fig. 17 – distribution of the invariant mass Mtt̄ for different masses of the Z’ with a luminosity of 200pb−1
(a) and distribution of this mass for the highest top and the highest antitop (b)
The figure 17 represents the invariant mass Mtt̄ when the top/antitop comes from the Z’. This studyhas been done for different masses of the Z’ and for 14TeV in the COM. We see here that the maximum ofthe distribution depends on the mass of the Z’.For the SM we use a random combination corresponding to all possible combinations between the tops andantitops and we take the average of this mass.
) [GeV]tM(t
400 600 800 1000 1200 1400
Nu
mb
er
of
even
ts/(
13G
eV
)
0
2
4
6
8
10
12
14
16
18
) [GeV]tM(t
400 600 800 1000 1200 1400
Nu
mb
er
of
even
ts/(
13G
eV
)
0
2
4
6
8
10
12
14
16
18
) for M(Z’)=500 GeVtdistribution of M(t
=14TeVs and -1L=200pb
from the Z’tt
tspectator t
random combination
SM
(a)
) [GeV]tM(t
500 1000 1500 2000
Nu
mb
er
of
even
ts/(
13G
eV
)
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
) [GeV]tM(t
500 1000 1500 2000
Nu
mb
er
of
even
ts/(
13G
eV
)
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
) for M(Z’)=1.2TeVtdistribution of M(t
=14TeVs and -1L=200pb
from the Z’tt
tspectator t
random combination
SM
(b)
Fig. 18 – distribution of the mass Mtt̄ for the top/antitop which come from the Z’, for the spectator tt̄and for a random combination of the (anti-)top for m(Z’)=500 GeV (a) and m(Z’)=1.2TeV (b)
The figure 18 represents the distribution of the mass Mtt̄ for the tt̄ from the Z’ and the spectator tt̄
13
t t invariant mass versus MZ’-
for t t from Z’-
3.3.4 top polarisation [4]
The polarisation of the top quarks is studied from the angular distribution of their decay products. Inthe decay channel t → W+b → l+ν the angular distribution of the particle X (X = W+, l+, ν) is given by :
1
Γ
dΓ
d cos θX=
1
2(1 + αX cos θX) (6)
where θX is the angle between the direction of X and the top spin axis in the top rest frame.
The constants αX take the values [8] :– αl+ = αd̄ = 1– αν = αu = −0.32– αW+ = −αb = 0.41
From the equation 6 we obtain the top production differential cross-section :
1
σ
dσ
d cos θX= FR + FL =
A
2(1 + αX cos θX) +
1 − A
2(1 − αX cos θX) = (A −
1
2)αX cos θX +
1
2(7)
top production differential cross-section
We study here the distribution of cos θl+ for M(Z’)=800 GeV and 14 TeV in the COM. For the SM wetake the lepton coming from the top with the highest Pt.
)!cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0.3
0.4
0.5
0.6
0.7
0.8
)!cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
0.3
0.4
0.5
0.6
0.7
0.8
Polarisation of the top
Z’ Model
SM
Z’ Model : A=0.78
SM : A=0.50
Fig. 21 – distribution of cos(θ) for the Exotic Model with a top right and for the SM
With a fit on the figure 21 thanks to the formula 7, we find :– A # 0.78 ± 0.18 for the exotic model with a right top– A # 0.50 ± 0.11 for the SM.
15
The value of the parameter A depends on the value of the mass of Z’. We can see this dependance onthe figure 22.
Z’M500 1000 1500 2000 2500
va
lue
of
A
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Z’Value of the polarisation versus M
(a)
Z’M500 1000 1500 2000 2500
va
lue
of
A
0.55
0.6
0.65
0.7
0.75
0.8
0.85
top from Z’
spectator top 1
spectator top 2
Z’Value of the polarisation versus M
(b)
Fig. 22 – value of the parameter A versus the mass of the Z’ for the tops (from the Z’ and spectator) (a)and value of this parameter for the top from the Z’, the closest (anti)top from the Z’ (spectator top 1) andthe other spectator (anti)top (spectator top 2) (b)
The value of the parameter A decrease at low masses of the Z’ because at low transverse momentumthe spin of the lepton has time to flip. For high masses of the Z’, the maximum value at 0.8 is due the massof the top [9]. If the top was massless we can expect that A ∼ 1.
3.3.5 Spin correlation
We consider here the distribution
1
N
d2N
d cos θ1.d cos θ2=
1
4(1 − A cos θ1 cos θ2 + b1 cos θ1 + b2 cos θ2) (8)
where θx is the angle between the direction of the lepton x in the top frame and the direction of thetop.We study here the same sign dilepton decay (the explanation about the choice of this channel is given inthe chapter 6).The leptons 1 and 2 represent the 2 leptons of same sign in the final state.
This distribution doesn’t depends on the mass of the Z’ for the top-philic model. But the distriutionfor the SM is very different. We have here a discriminant variable.
After a fit on the figure 23 we find the coefficients A, b1 and b2 of the formula 8.
- Z’(500GeV) Z’(1TeV) Z’(1.5TeV) SMA -0.25 -0.23 -0.31 0.038b1 0.44 0.55 0.54 -0.0073b2 0.41 0.55 0.60 -0.03
Tab. 2 – Value of the coefficient A for the SM and the signal for differents masses of Z’
16
top polarization
The lightest mass eigenstate is identified as the top quark. It can have a large coupling to Z ′ through its
ψ component.
Four-top production arises via the diagrams shown in Fig. 3. Given that the Z ′ under consideration
has suppressed couplings to all SM fields (induced by the kinetic mixing χ) but the top quarks, constraintsare weak and a mass of a few hundreds of GeV is allowed, which can lead to large four-top signals at the
LHC. A detailed study is presented in [14] and compares with the non-resonant four-top events obtained
from the effective four-fermion interaction (tRγµtR)(tRγµtR)/Λ2 leading to the diagram 1(d). The
corresponding cross sections at LHC as a function of the Z ′ mass and Λ are shown in Fig. 2.
t
t
t
t−
−Z’
t
t
t
t
−
−
Z’
Fig. 3: Four-top production via Z ′
An interesting way to probe the properties of the top interactions relies on measuring the top
polarization. The SM four top production being dominated by parity invariant QCD processes, we expect
to generate an equal number of left and right-handed pairs. However, in the new physics models discussed
here, there is a strong bias towards RH tops. The angular distribution of the leptons from the top decays
enables to analyze the polarisation of the top quarks. The differential cross section can be written as
1
σ
dσ
d cos θ=
A
2(1 + cos θ) +
1 − A
2(1 − cos θ) (3)
where θ is the angle between the direction of the lepton in the top rest frame and the direction of the toppolarization. The corresponding distribution is illustrated in Fig. 4.
In Fig. 5, we show the invariant mass Mtt of the tt pair coming from the Z ′ for different MZ′
masses as well as Mtt from the SM four-top events. The latter peaks close to 600 GeV. We also display
the maximum of the tt pair transverse energy distribution as a function ofMZ′ . Fig. 6 compares theMtt
distributions of the tt pair emitted by a Z ′ withMZ′ = 1.2 TeV, the spectator tt pair, which peaks around500 GeV and the tt pair produced by the effective 4-fermion contact interaction.
3. RECONSTRUCTION
Reconstruction of four top events is a challenge to the detector and event reconstruction. The decay of the
top quarks gives rise to twelve fermions. To benefit from the same-sign lepton signature two W bosons
must decay to lepton-neutrino. The presence of two escaping neutrinos then prevents a complete recon-
struction of the twelve momenta. In the most abundantly produced final states, most of the remaining
fermions will be quarks, giving rise to a large jet multiplicity.
The minimal approach to reconstruction merely registers the scalar sum of the transverse energy
of all final state objects. The HT distribution for a 500 GeV and 1 TeV Z’ resonance as described in
the previous section are shown in Figure 7. For sufficiently large resonance mass, i.e. for mZ′ = 1
TeV in the central panel, the signal distribution clearly differs from that of some important (reducible)
backgrounds like tt̄W±+ jets and tt̄W+W−.
A further experimental signature of the four-top final states is the large b-jet multiplicity which
can be used as a powerful tool to extract the signal even coming from a heavy resonance as shown in
θ is the angle between the direction of the (highest pT) lepton in the top rest frame and the direction of the top polarisation
A: fraction of RH tops
In the models of interest, 4-top production yields an excess of right-handed tops
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
angle_leptons
Entries 4849Mean x 0.1304Mean y 0.1412RMS x 0.5607RMS y 0.5543
angle_leptons
Entries 4849Mean x 0.1304Mean y 0.1412RMS x 0.5607RMS y 0.5543
for M(Z’)=500GeV)
2!).dcos(
1!dcos(
.N2d.
N1
(a)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.005
0.01
0.015
0.02
0.025
angle_leptons
Entries 3825Mean x 0.1806
Mean y 0.1739
RMS x 0.5498RMS y 0.5491
angle_leptons
Entries 3825Mean x 0.1806
Mean y 0.1739
RMS x 0.5498RMS y 0.5491 for M(Z’)=1TeV
)2!).dcos(
1!dcos(
.N2d.
N1
(b)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.005
0.01
0.015
0.02
0.025
0.03
angle_leptons
Entries 2478Mean x 0.1953Mean y 0.1798RMS x 0.5487RMS y 0.5535
angle_leptons
Entries 2478Mean x 0.1953Mean y 0.1798RMS x 0.5487RMS y 0.5535
for M(Z’)=1.5TeV)
2!).dcos(
1!dcos(
.N2d.
N1
(c)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.006
0.008
0.01
0.012
0.014
0.016
0.018
angle_leptonsEntries 2126Mean x -0.007526Mean y -0.0007526RMS x 0.5736RMS y 0.5785
angle_leptonsEntries 2126Mean x -0.007526Mean y -0.0007526RMS x 0.5736RMS y 0.5785
for the SM)
2!).dcos(
1!dcos(
.N2d.
N1
(d)
Fig. 23 – distribution of d2Nd cos θ1.d cos θ2
for different masses of the Z’ (a) to (c) and for the SM (d)
3.3.6 Opening angle
The opening angle is the angle between the momentum of the lepton l+ in the top frame and themomentum of the lepton l− in the antitop frame.We see on the figure 24 that this variable is not discriminant.
)"cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
)"
dco
s(
dN
.N1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
)"cos(-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1
)"
dco
s(
dN
.N1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Opening angle
from the Z’ for m(Z’)=350GeVtt
for m(Z’)=350GeVtspectator t
from the Z’ for m(Z’)=2TeVtt
for m(Z’)=2TeVtspectator t
SM
Fig. 24 – distribution of the opening angle for the SM and the signal with : the tt̄ from the Z’ and thespectator tt̄
17
Spin correlations3.3.5 Spin correlation
We consider here the distribution
1
N
d2N
d cos θ1.d cos θ2=
1
4(1 − A cos θ1 cos θ2 + b1 cos θ1 + b2 cos θ2) (8)
where θx is the angle between the direction of the lepton x in the top frame and the direction of thetop.We study here the same sign dilepton decay (the explanation about the choice of this channel is given inthe chapter 6).The leptons 1 and 2 represent the 2 leptons of same sign in the final state.
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
angle_leptons
Entries 4849Mean x 0.1304Mean y 0.1412RMS x 0.5607RMS y 0.5543
angle_leptons
Entries 4849Mean x 0.1304Mean y 0.1412RMS x 0.5607RMS y 0.5543
for M(Z’)=500GeV)
2!).dcos(
1!dcos(
.N2d.
N1
(a)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.005
0.01
0.015
0.02
0.025
angle_leptons
Entries 3825Mean x 0.1806
Mean y 0.1739
RMS x 0.5498RMS y 0.5491
angle_leptons
Entries 3825Mean x 0.1806
Mean y 0.1739
RMS x 0.5498RMS y 0.5491 for M(Z’)=1TeV
)2!).dcos(
1!dcos(
.N2d.
N1
(b)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.005
0.01
0.015
0.02
0.025
0.03
angle_leptons
Entries 2478Mean x 0.1953Mean y 0.1798RMS x 0.5487RMS y 0.5535
angle_leptons
Entries 2478Mean x 0.1953Mean y 0.1798RMS x 0.5487RMS y 0.5535
for M(Z’)=1.5TeV)
2!).dcos(
1!dcos(
.N2d.
N1
(c)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.006
0.008
0.01
0.012
0.014
0.016
0.018
angle_leptonsEntries 2126Mean x -0.007526Mean y -0.0007526RMS x 0.5736RMS y 0.5785
angle_leptonsEntries 2126Mean x -0.007526Mean y -0.0007526RMS x 0.5736RMS y 0.5785
for the SM)
2!).dcos(
1!dcos(
.N2d.
N1
(d)
Fig. 24 – distribution of d2Nd cos θ1.d cos θ2
for different masses of the Z’ (a) to (c) and for the SM (d)
This distribution doesn’t depends on the mass of the Z’ for the top-philic model. But the distriutionfor the SM is very different. We have here a discriminant variable.
After a fit on the figure 24 we find the coefficients A, b1 and b2 of the formula 8.
- Z’(500GeV) Z’(1TeV) Z’(1.5TeV) SMA -0.14±0.29 -0.22±0.27 -0.26±0.23 -0.11±0.3b1 0.43±0.32 0.56±0.32 0.64±0.29 -0.0051±0.29b2 0.53±0.32 0.61±0.31 0.57±0.33 -0.03±0.29
Tab. 2 – Value of the coefficient A, b1 and b2 for the SM and the signal for differents masses of Z’
17
3.3.5 Spin correlation
We consider here the distribution
1
N
d2N
d cos θ1.d cos θ2=
1
4(1 − A cos θ1 cos θ2 + b1 cos θ1 + b2 cos θ2) (8)
where θx is the angle between the direction of the lepton x in the top frame and the direction of thetop.We study here the same sign dilepton decay (the explanation about the choice of this channel is given inthe chapter 6).The leptons 1 and 2 represent the 2 leptons of same sign in the final state.
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0.018
0.02
angle_leptons
Entries 4849Mean x 0.1304Mean y 0.1412RMS x 0.5607RMS y 0.5543
angle_leptons
Entries 4849Mean x 0.1304Mean y 0.1412RMS x 0.5607RMS y 0.5543
for M(Z’)=500GeV)
2!).dcos(
1!dcos(
.N2d.
N1
(a)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.005
0.01
0.015
0.02
0.025
angle_leptons
Entries 3825Mean x 0.1806
Mean y 0.1739
RMS x 0.5498RMS y 0.5491
angle_leptons
Entries 3825Mean x 0.1806
Mean y 0.1739
RMS x 0.5498RMS y 0.5491 for M(Z’)=1TeV
)2!).dcos(
1!dcos(
.N2d.
N1
(b)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.005
0.01
0.015
0.02
0.025
0.03
angle_leptons
Entries 2478Mean x 0.1953Mean y 0.1798RMS x 0.5487RMS y 0.5535
angle_leptons
Entries 2478Mean x 0.1953Mean y 0.1798RMS x 0.5487RMS y 0.5535
for M(Z’)=1.5TeV)
2!).dcos(
1!dcos(
.N2d.
N1
(c)
cos theta1-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1cos theta2
-1-0.8
-0.6-0.4
-0.20
0.20.4
0.60.81
0.006
0.008
0.01
0.012
0.014
0.016
0.018
angle_leptonsEntries 2126Mean x -0.007526Mean y -0.0007526RMS x 0.5736RMS y 0.5785
angle_leptonsEntries 2126Mean x -0.007526Mean y -0.0007526RMS x 0.5736RMS y 0.5785
for the SM)
2!).dcos(
1!dcos(
.N2d.
N1
(d)
Fig. 24 – distribution of d2Nd cos θ1.d cos θ2
for different masses of the Z’ (a) to (c) and for the SM (d)
This distribution doesn’t depends on the mass of the Z’ for the top-philic model. But the distriutionfor the SM is very different. We have here a discriminant variable.
After a fit on the figure 24 we find the coefficients A, b1 and b2 of the formula 8.
- Z’(500GeV) Z’(1TeV) Z’(1.5TeV) SMA -0.14±0.29 -0.22±0.27 -0.26±0.23 -0.11±0.3b1 0.43±0.32 0.56±0.32 0.64±0.29 -0.0051±0.29b2 0.53±0.32 0.61±0.31 0.57±0.33 -0.03±0.29
Tab. 2 – Value of the coefficient A, b1 and b2 for the SM and the signal for differents masses of Z’
17
!"
Gauthier L – Servant G – Etienvre A.I GDR Terascale 31 mars 2010 10
Same sign dilepton channel (e or µ)
!"#$%&& '()*+, '-./012123()*+,
&45671(809:3(;(<==>%? @A@-B@ BC-<
&45671(809:3(;(B(D%? EB-BF B-A
GGGG C-<H =-B<
GGII BH=-@ <-B
GGI(J(0=KBKH3(L%G& <F< B@-M
III(J(0=KBKH3(L%G& E=A B@-C
II(J(0=KBKHKAKM3(L%G& AHM B<-<
The same sign dilepton channel eliminates the background tt ( = 800 pb! )
" We don't take into account the detector effect
similar final state studied in Contino-Servant' 08
background in same-sign dilepton channel @LHC
final state: l± l± + n jets + ET
(of which 4 are b-jets)
➙
tt+jets with charge mis-ID not included here (but will be)-
6.2 Study with the jets
We work here with a b-efficiency of 100% and no mistage for the light jets.
6.2.1 Study on the jets
>30GeVT
total number of jets if P0 2 4 6 8 10 12
0
0.1
0.2
0.3
0.4
0.5
>30GeVT
total number of jets if P0 2 4 6 8 10 12
0
0.1
0.2
0.3
0.4
0.5signal
ttpp -> tt-
W+Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
(a)
>30GeVT
number of b-jets if P0 1 2 3 4 5 6 7
0
0.2
0.4
0.6
0.8
1
>30GeVT
number of b-jets if P0 1 2 3 4 5 6 7
0
0.2
0.4
0.6
0.8
1 signal
ttpp -> tt-
W+
Wtpp -> t
+ jets±Wtpp -> t
+ jets±W-
W+
pp -> W
+ jets±W±pp -> W
(b)
>30GeVT
total number of jet if P2 4 6 8 10 12 14
0
0.05
0.1
0.15
0.2
0.25
>30GeVT
total number of jet if P2 4 6 8 10 12 14
0
0.05
0.1
0.15
0.2
0.25m(Z’)=500GeV
m(Z’)=1TeV
m(Z’)=1.5TeV
(c)
Fig. 53 – Distribution of the total number of jets for Pt > 30GeV (a), distribution of the number of b jetsfor Pt > 15GeV (b) and distribution of the total number of jets for different masses of the Z’ (c). Thesedistributions are normalized to 1 and the jet cone size is ∆R = 0.4.
34
6.2 Study with the jets
We work here with a b-efficiency of 100% and no mistage for the light jets.
6.2.1 Study on the jets
>30GeVT
total number of jets if P0 2 4 6 8 10 12
0
0.1
0.2
0.3
0.4
0.5
>30GeVT
total number of jets if P0 2 4 6 8 10 12
0
0.1
0.2
0.3
0.4
0.5signal
ttpp -> tt-
W+Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
(a)
>30GeVT
number of b-jets if P0 1 2 3 4 5 6 7
0
0.2
0.4
0.6
0.8
1
>30GeVT
number of b-jets if P0 1 2 3 4 5 6 7
0
0.2
0.4
0.6
0.8
1 signal
ttpp -> tt-
W+
Wtpp -> t
+ jets±Wtpp -> t
+ jets±W-
W+
pp -> W
+ jets±W±pp -> W
(b)
>30GeVT
total number of jet if P2 4 6 8 10 12 14
0
0.05
0.1
0.15
0.2
0.25
>30GeVT
total number of jet if P2 4 6 8 10 12 14
0
0.05
0.1
0.15
0.2
0.25m(Z’)=500GeV
m(Z’)=1TeV
m(Z’)=1.5TeV
(c)
Fig. 53 – Distribution of the total number of jets for Pt > 30GeV (a), distribution of the number of b jetsfor Pt > 15GeV (b) and distribution of the total number of jets for different masses of the Z’ (c). Thesedistributions are normalized to 1 and the jet cone size is ∆R = 0.4.
34
# of jets
four-top events from a top-philic Z’ @LHC in same-sign dilepton channel
nb jets ! 3preliminary
) [GeV]tM(t
400 600 800 1000 1200 1400 1600 1800
]-1
[G
eV
)td
M(t !
d !1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
) [GeV]tM(t
400 600 800 1000 1200 1400 1600 1800
]-1
[G
eV
)td
M(t !
d !1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
)tdistribution of M(t
from the Z’ for M(Z’)=1.2TeVtt
for M(Z’)=1.2TeVtspectator t
random combination for M(Z’)=1.2TeV
SM
= 500GeV"effective model for
Fig. 6: Comparison of the different tt invariant mass distributions.
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
2
4
6
8
10
12
14
16
18
20
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
2
4
6
8
10
12
14
16
18
20=14TeVs, -1L = 10fb
= 500GeVZ’
signal M
ttpp -> tt-
W+
Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
2
4
6
8
10
12
14
16
18
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
2
4
6
8
10
12
14
16
18 =14TeVs, -1L = 100fb = 1TeV
Z’signal M
ttpp -> tt-
W+Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
2
4
6
8
10
12
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
2
4
6
8
10
12 =14TeVs, -1L = 100fb = 1TeV
Z’signal M
ttpp -> tt-
W+Wtpp -> t + jets±Wtpp -> t
+ jets±W-
W+pp -> W + jets±W±pp -> W
Fig. 7: Total transverse energy after demanding nj ≥ 6, pT > 30 GeV (first two plots) and in addition nb−jet ≥ 3
(third plot).
tt̄H topology. An alternative approach presents itself when one considers the reconstruction of tt̄ eventsoriginating in the decay of a heavy resonance. Due to the boost of the top quark, its decay products
are collimated in a narrow cone. This top mono-jet can be identified as such by techniques revealing
the jet substructure [15, 9, 16, 17, 18, 19]. Importantly, for sufficiently large resonance mass the decay
products of top and anti-top are cleanly separated. A simple assignment based on (geometrical) vicinity
is sufficient to find the correct assignment of jets to top candidates. Thus, the ambiguities found in
reconstruction of “tops at rest” disappear in regime of large top pT .
To quantify this statement a parton level simulation of pp → X → tt̄ has been analysed. Lep-ton+jets events are selected, where one of the W bosons decays to a lepton and a neutrino and the second
MZ′ = 500 GeV MZ′ = 1 TeV
) [GeV]tM(t
400 600 800 1000 1200 1400 1600 1800
]-1
[G
eV
)td
M(t !
d !1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
) [GeV]tM(t
400 600 800 1000 1200 1400 1600 1800
]-1
[G
eV
)td
M(t !
d !1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
)tdistribution of M(t
from the Z’ for M(Z’)=1.2TeVtt
for M(Z’)=1.2TeVtspectator t
random combination for M(Z’)=1.2TeV
SM
= 500GeV"effective model for
Fig. 6: Comparison of the different tt invariant mass distributions.
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18
20
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18
20=14TeVs, -1L = 10fb
= 500GeVZ’
signal M
ttpp -> tt-
W+
Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18 =14TeVs, -1L = 100fb = 1TeV
Z’signal M
ttpp -> tt-
W+Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12 =14TeVs, -1L = 100fb = 1TeV
Z’signal M
ttpp -> tt-
W+Wtpp -> t + jets±Wtpp -> t
+ jets±W-
W+pp -> W + jets±W±pp -> W
Fig. 7: Total transverse energy after demanding nj ≥ 6, pT > 30 GeV (first two plots) and in addition nb−jet ≥ 3
(third plot).
tt̄H topology. An alternative approach presents itself when one considers the reconstruction of tt̄ eventsoriginating in the decay of a heavy resonance. Due to the boost of the top quark, its decay products
are collimated in a narrow cone. This top mono-jet can be identified as such by techniques revealing
the jet substructure [15, 9, 16, 17, 18, 19]. Importantly, for sufficiently large resonance mass the decay
products of top and anti-top are cleanly separated. A simple assignment based on (geometrical) vicinity
is sufficient to find the correct assignment of jets to top candidates. Thus, the ambiguities found in
reconstruction of “tops at rest” disappear in regime of large top pT .
To quantify this statement a parton level simulation of pp → X → tt̄ has been analysed. Lep-ton+jets events are selected, where one of the W bosons decays to a lepton and a neutrino and the second
with b-tagging efficiency=1
6.3 Study with a b-efficiency of 60% (extrapolation).
In order to extrapolate the results for an efficiency of 60%, we renormalize the distributions with nb-jets by 0.6n.In the figure ?? the distributions for one b-efficiency are added.
[GeV] TH
500 1000 1500 2000
Nu
mb
er
of
eve
nts
/(50
GeV
)
0
2
4
6
8
10
12
14
16
18
20
[GeV] TH
500 1000 1500 2000
Nu
mb
er
of
eve
nts
/(50
GeV
)
0
2
4
6
8
10
12
14
16
18
20=500GeV
Z’=14TeV, Ms,
-1L = 10fb
signal, b-efficiency=1
background, b-efficiency=1
signal, b-efficiency=0.6
background, b-efficiency=0.6
[GeV] TH
500 1000 1500 2000 2500
Nu
mb
er
of
ev
en
ts/(
50
GeV
)
0
2
4
6
8
10
12
14
[GeV] TH
500 1000 1500 2000 2500
Nu
mb
er
of
ev
en
ts/(
50
GeV
)
0
2
4
6
8
10
12
14=1TeV
Z’=14TeV, Ms, -1L = 100fb
signal, b-efficiency=1
background, b-efficiency=1
signal, b-efficiency=0.6
background, b-efficiency=0.6
Fig. 69 – Distribution of HT for b-efficiency=100% and b-efficiency=60% for nb total jets ≥ 6, nb b jets≥3 and pT > 30GeV
[GeV] TH
500 1000 1500 2000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
0.5
1
1.5
2
2.5
3
3.5
[GeV] TH
500 1000 1500 2000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
0.5
1
1.5
2
2.5
3
3.5
=500GeVZ’
=14TeV, Ms, -1L = 10fb
signal, b-efficiency=0.6
background, b-efficiency=0.6
[GeV] TH
500 1000 1500 2000 2500
Nu
mb
er
of
even
ts/(
50G
eV
)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
[GeV] TH
500 1000 1500 2000 2500
Nu
mb
er
of
even
ts/(
50G
eV
)
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4=1TeV
Z’=14TeV, Ms, -1L = 100fb
signal, b-efficiency=0.6
background, b-efficiency=0.6
Fig. 70 – Distribution of HT if b-efficiency=60% for nb total jets ≥ 6, nb b jets ≥3 and pT > 30GeV
In the table ?? are reported the number of events and background extrapolated for a b-efficiency of60% :
44
with b-tagging efficiency of 60%
MZ’ =500 GeV 5σ excess luminosity~ 150 pb-1
MZ’ =1 TeV 5σ excess luminosity~ 25 fb-1
Λ = 500 GeV 5σ excess luminosity~ 15 fb-1
preliminary
) [GeV]tM(t
400 600 800 1000 1200 1400 1600 1800
]-1
[G
eV
)td
M(t !
d !1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
) [GeV]tM(t
400 600 800 1000 1200 1400 1600 1800
]-1
[G
eV
)td
M(t !
d !1
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
)tdistribution of M(t
from the Z’ for M(Z’)=1.2TeVtt
for M(Z’)=1.2TeVtspectator t
random combination for M(Z’)=1.2TeV
SM
= 500GeV"effective model for
Fig. 6: Comparison of the different tt invariant mass distributions.
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18
20
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18
20=14TeVs, -1L = 10fb
= 500GeVZ’
signal M
ttpp -> tt-
W+
Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
14
16
18 =14TeVs, -1L = 100fb = 1TeV
Z’signal M
ttpp -> tt-
W+Wtpp -> t
+ jets±Wtpp -> t + jets±W
-W
+pp -> W
+ jets±W±pp -> W
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12
[GeV]TH
500 1000 1500 2000 2500 3000
Nu
mb
er
of
even
ts/(
50G
eV
)
0
2
4
6
8
10
12 =14TeVs, -1L = 100fb = 1TeV
Z’signal M
ttpp -> tt-
W+Wtpp -> t + jets±Wtpp -> t
+ jets±W-
W+pp -> W + jets±W±pp -> W
Fig. 7: Total transverse energy after demanding nj ≥ 6, pT > 30 GeV (first two plots) and in addition nb−jet ≥ 3
(third plot).
tt̄H topology. An alternative approach presents itself when one considers the reconstruction of tt̄ eventsoriginating in the decay of a heavy resonance. Due to the boost of the top quark, its decay products
are collimated in a narrow cone. This top mono-jet can be identified as such by techniques revealing
the jet substructure [15, 9, 16, 17, 18, 19]. Importantly, for sufficiently large resonance mass the decay
products of top and anti-top are cleanly separated. A simple assignment based on (geometrical) vicinity
is sufficient to find the correct assignment of jets to top candidates. Thus, the ambiguities found in
reconstruction of “tops at rest” disappear in regime of large top pT .
To quantify this statement a parton level simulation of pp → X → tt̄ has been analysed. Lep-ton+jets events are selected, where one of the W bosons decays to a lepton and a neutrino and the second
nb jets ! 3with only the very simple cuts:
,
(gZ′
tR= 3)
[GeV]T,missE
0 100 200 300 400 500 600 700 800 900 1000
Nu
mb
er
of
ev
en
ts/(
20
Ge
V)
0
0.5
1
1.5
2
2.5
[GeV]T,missE
0 100 200 300 400 500 600 700 800 900 1000
Nu
mb
er
of
ev
en
ts/(
20
Ge
V)
0
0.5
1
1.5
2
2.5
=14TeVs, -1L = 100fb
m(Z’)=800GeV
m(Z’)=1TeV
m(Z’)=1.2TeV
SM
(a)
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
0.5
1
1.5
2
2.5
[GeV]TH
500 1000 1500 2000 2500
Nu
mb
er
of
ev
en
ts/(
50
Ge
V)
0
0.5
1
1.5
2
2.5
=14TeVs, -1L = 100fb
m(Z’)=800GeV
m(Z’)=1TeV
m(Z’)=1.2TeV
SM
(b)
Fig. 43 – Distribution of the transverse missing energy (a) and the total transverse energy for differentmasses of the Z’ and the SM
It seems that the maximum of the total transverse energy depends on the mass of the Z’. We plot thetotal transverse energy versus the mass of the Z’.
M(Z’) [GeV]400 600 800 1000 1200 1400 1600
Tm
axim
um
of
H
700
800
900
1000
1100
1200
1300
1400
1500 / ndf 2! 2.041 / 5
origine (signal) 77.68± 598.9
slope (signal) 0.1163± 0.5555
/ ndf 2! 2.041 / 5
origine (signal) 77.68± 598.9
slope (signal) 0.1163± 0.5555
versus M(Z’)TH
Fig. 44 – total transverse energy versus the mass of the Z’
Thanks to a fit on the figure 5.3, we find :– slope of the curve : 0.55551 ± 0.12– origin of the curve : 598.941 ± 77.68
27
Max of
Mtt (GeV)0 500 1000 1500 2000 2500
Fra
ction o
f events
0
0.2
0.4
0.6
0.8
1
(a)
mass (GeV)tt
0 500 1000 1500 2000 2500
-1events
/50 G
eV
/100 fb
0
1
2
3
4
5
6
7
(b)
reconstructed mass (GeV)0 500 1000 1500 2000 2500
-1events
/50 G
eV
/100 fb
0
1
2
3
4
5
6
7
(c)
Fig. 8: The probability as a function of resonance mass that final state fermions are correctly assigned to top and anti-top
quarks in tt̄ production (open circles) and tt̄tt̄ production. The filled circles (triangles) indicate the probability to find two
(four) correctly paired top quarks. The central panel shows the invariant mass distribution of the two top quarks with highest
pT in SM tt̄tt̄ production (filled histogram) and for production through a 1.5 TeV KK gluon. The rightmost panel shows the
invariant mass of the two reconstructed clusters with highest pT .
W boson decay to two jets. The neutrino is discarded and the momenta of the remaining five fermions
is presented to the kT algorithm [20, 21] for clustering 3. Clustering is considered correct whenever
all decay products from the top (and anti-top) quark are clustered together in a single jet. The result is
represented with open circles in the leftmost plot of figure 8. For tops produced at rest the probability
of correctly clustering the event is essentially equal to 0. For resonant tt̄ production the probability tofind the correct assignment increases rapidly as the resonance mass is increased. The decay products of
the top and anti-top quark are collimated more and more in a narrow cone, while the top anti-top are
emitted essentially back-to-back. Indeed, for a resonance mass of 1 TeV, the correct assignment is found
in nearly eighty percent of events. For a more exhaustive discussion, and results including a complete
detector simulation the reader is referred to reference [23].
When repeating the exercise for tt̄tt̄ production, the simple clustering has to deal with a muchdenser topology and is much less successful. As shown with blue triangles in figure 8 the probability to
find a perfectly clustered event is less than 10 % over the entire mass range studied here. Of course, the
decay of a heavy resonance leads to only one pair of strongly boosted top quarks, while the pT of the
associated (spectator) top quarks remains relatively small. The third curve (filled circles) in 8 represents
the probability that at least two tops out of four are clustered correctly. This probability is quite large
even for relatively small resonance mass, reaching approximately 60 % for a 1 TeV resonance.
The mass of the resonance is reconstructed as the invariant mass of the two objects with highest
pT in the event. At the parton level this yields good results: the combination of the two top quarks
with highest pT yields the distribution of the central panel of figure 8. The resonance clearly stands out
on top of the SM four top production (black). Applying the same criterion to the top quark candidates
reconstructed by the clustering algorithm, the distribution in the rightmost panel is obtained. Obviously,
the resonant signature is washed out by false combinations and the energy carried away by the escaping
neutrinos. Still, the signal and background distributions can clearly be distinguished.
The additional handle of highly boosted top quarks is found to be quite useful to reduce the com-
binatoric problem of four top events. Reconstruction of a resonant signature may well be feasible, thus
turning the counting experiment into a resonance search. Given the simple-minded nature of this attempt
3The implementation in FastJet [22] was used, with E-scheme recombination. The algorithms was used in exclusive mode,
forcing it to return exactly two jets. The R-parameter was set to 2.5. For this, somewhat unusual, choice nearly all input objects
are clustered into jets (rather than included in the “beam jets”).
Top reconstruction
Mtt (GeV)0 500 1000 1500 2000 2500
Fra
ctio
n o
f e
ve
nts
0
0.2
0.4
0.6
0.8
1
(a)
mass (GeV)tt
0 500 1000 1500 2000 2500
-1eve
nts
/50
GeV
/100
fb
0
1
2
3
4
5
6
7
(b)
reconstructed mass (GeV)0 500 1000 1500 2000 2500
-1e
ve
nts
/50
Ge
V/1
00
fb
0
1
2
3
4
5
6
7
(c)
Fig. 8: The probability as a function of resonance mass that final state fermions are correctly assigned to top and anti-top
quarks in tt̄ production (open circles) and tt̄tt̄ production. The filled circles (triangles) indicate the probability to find two
(four) correctly paired top quarks. The central panel shows the invariant mass distribution of the two top quarks with highest
pT in SM tt̄tt̄ production (filled histogram) and for production through a 1.5 TeV KK gluon. The rightmost panel shows the
invariant mass of the two reconstructed clusters with highest pT .
W boson decay to two jets. The neutrino is discarded and the momenta of the remaining five fermions
is presented to the kT algorithm [20, 21] for clustering 3. Clustering is considered correct whenever
all decay products from the top (and anti-top) quark are clustered together in a single jet. The result is
represented with open circles in the leftmost plot of figure 8. For tops produced at rest the probability
of correctly clustering the event is essentially equal to 0. For resonant tt̄ production the probability tofind the correct assignment increases rapidly as the resonance mass is increased. The decay products of
the top and anti-top quark are collimated more and more in a narrow cone, while the top anti-top are
emitted essentially back-to-back. Indeed, for a resonance mass of 1 TeV, the correct assignment is found
in nearly eighty percent of events. For a more exhaustive discussion, and results including a complete
detector simulation the reader is referred to reference [23].
When repeating the exercise for tt̄tt̄ production, the simple clustering has to deal with a muchdenser topology and is much less successful. As shown with blue triangles in figure 8 the probability to
find a perfectly clustered event is less than 10 % over the entire mass range studied here. Of course, the
decay of a heavy resonance leads to only one pair of strongly boosted top quarks, while the pT of the
associated (spectator) top quarks remains relatively small. The third curve (filled circles) in 8 represents
the probability that at least two tops out of four are clustered correctly. This probability is quite large
even for relatively small resonance mass, reaching approximately 60 % for a 1 TeV resonance.
The mass of the resonance is reconstructed as the invariant mass of the two objects with highest
pT in the event. At the parton level this yields good results: the combination of the two top quarks
with highest pT yields the distribution of the central panel of figure 8. The resonance clearly stands out
on top of the SM four top production (black). Applying the same criterion to the top quark candidates
reconstructed by the clustering algorithm, the distribution in the rightmost panel is obtained. Obviously,
the resonant signature is washed out by false combinations and the energy carried away by the escaping
neutrinos. Still, the signal and background distributions can clearly be distinguished.
The additional handle of highly boosted top quarks is found to be quite useful to reduce the com-
binatoric problem of four top events. Reconstruction of a resonant signature may well be feasible, thus
turning the counting experiment into a resonance search. Given the simple-minded nature of this attempt
3The implementation in FastJet [22] was used, with E-scheme recombination. The algorithms was used in exclusive mode,
forcing it to return exactly two jets. The R-parameter was set to 2.5. For this, somewhat unusual, choice nearly all input objects
are clustered into jets (rather than included in the “beam jets”).
[figures from Marcel Vos]
challenge of assigning 12 final state fermion particles to the 4 top candidates.
(from 1005.1229)
$e top quark-Dark Ma%er connection
Z, Z’
!
h
t
"
"
~ O(1) couplings
Dirac Dark Matter annihilation into γ H
Jackson, Servant, Shaughnessy,Tait, Taoso,’09
NFW profile adiabaticallycontracted
γ-ray lines from the Galactic Center ΔΩ= 10-5 sr
Spectra for parameters leading to correct relic density and satisfying
direct detection constraints
MΝ"149 GeV !gΝZ'"gtZ'"3" MΝ"162 GeV !gΝZ'"gtZ'"1"Γ h$ Mh"170 GeVΓ Z %$ MZ'"220 GeV Γ Z
HESS
EGRET
FERMI
1 10 10210!1610!1510!1410!1310!1210!1110!1010!910!810!710!610!510!4
EΓ !GeV"
E2d##dE!G
eVcm!2 s!1 "
Jackson, Servant, Shaughnessy,Tait, Taoso,’09
Higgs in Space!
Z’ H Z
ff → Z ′ → tt
ff → Z ′ → γH
gg → tt + Z ′
tt + ET
tttt
Z′ →
νν
Z ′→tt
light tt resonances
energetic monochromatic γ
Z, Z’
!
h
t
"
"e−
e+
q
q
●
●
●
●
ν ν t
t -- or
-t
t Z’
Collider signatures of a top (and DM)-philic Z’
four-top events at Multi-TeV e+e- colliders
Σee" ttZ' # !1.5$1.5" TeVgtRZ' % 3
100 200 300 400 500 6000
10
20
30
40
MZ' !GeV"
fb
e
e
−
+
t
t−
− −
Z’
t, N
t, N
Battaglia-Servant 1005.4632
0.2 ab-1
e+ e- → t t + ET @ 3 TeV CLIC - σttνeνe = 4.1 fb σ4t in SM = 0.03 fb
tt Invariant Mass (GeV)0 500 1000 1500 2000 2500 3000
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tries
/ 0.
2 ab
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80Full Sim + Reco M(Z’)=200 GeV
Generated M(Z’)=200 GeV
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ents
/ 20
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MZ’ =200 GeV
(gZ′
tR= gZ′
DM = 3)
MZ’ =360 GeV
e+ e- → t t t t @ 3 TeV CLIC -
Di-Jet Invariant Mass (GeV)500 1000
-1Di
-Jet
s / 1
ab
0
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h9105Entries 430Mean 529.8RMS 198.3Underflow 0Overflow 28.44Integral 436.1
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-
(gZ′
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Summary
four-tops: key channel to probe top compositeness (although not at 7 TeV)
we found good prospects in the very clean 2 same-sign dilepton channel
b-tagging crucial to probe the O(10 fb) cross sections
future plans: full ATLAS simulation (events already generated at 7 TeV)
four-top events: in a large class of BSM models (susy, top composite models, top-philic resonances )
so far, there was no detailed study
