5.2 Resonances Coupling to Third Generation Quarks
139
1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
10
1
−
10
1
10
2
10
3
10
4
10
5
10
Events / 40 GeV
Data
σ
1
±
Background
= 2 TeV
Z'
Signal m
= 3 TeV
Z'
Signal m
ATLAS
-1
= 13TeV, 139 fb
s
γ
H
→
Z'
→
q
q
single b-tagged
(a)
1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
1
−
0
1
2
Significance
1000 1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
10
1
−
10
1
10
2
10
3
10
4
10
5
10
Events / 40 GeV
Data
σ
1
±
Background
= 2 TeV
Z'
Signal m
= 3 TeV
Z'
Signal m
ATLAS
-1
= 13TeV, 139 fb
s
γ
H
→
Z'
→
q
q
double b-tagged
(b)
1000 1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
1
−
0
1
2
Significance
Fig. 5.6 Distributions in the reconstructed H γ mass obtained by ATLAS from events with a
high- p T photon and an H -tagged jet. Events are categorised into H jets with a single b tag (left)
and a double b tag (right). The background is modelled by a parametric function with three free
parameters. Taken from [785]
5.2 Resonances Coupling to Third Generation Quarks
In certain BSM models, the couplings of heavy resonances to third generation quarks
is enhanced. This includes Kaluza-Klein excitations of gluons [39, 786] or gravitons [787, 788], massive colour-singlet W
and Z
bosons [789–793], colourons [794–
796], axigluons [797, 798], and pseudoscalar Higgs bosons [628, 679, 799]. In some
models of warped extra dimensions [699], resonance decays into bosons or third
generation quarks can be important, depending on the nature of the resonance and the
choice of free parameters [800]. For heavy neutral resonances, decays to bb would be
observable in dijet searches with b-tagged jets (see for example [801]), but decays to
tt result in distinct final states. Dedicated analyses are needed for optimal sensitivity,
reconstructing the tt system from its visible decay products. The decay of a narrow
resonance would be observable as a peak above the falling spectrum in the mass of
the tt system, m tt . Searches of this kind are probing the highest energy scales in tt
production, thus also testing our models used to simulate these final states. Charged
resonances would preferably decay to tb or its charge conjugate, if the couplings to
first and second generation quarks are suppressed. While also leptonic decays of the
kind W
→ ν are possible, these are forbidden for purely right-handed couplings of
the W
boson if the right-handed neutrino is heavier than a few GeV [802]. Similar
to tt resonance searches, a structure in the mass of the tb system is searched for.
139
1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
10
1
−
10
1
10
2
10
3
10
4
10
5
10
Events / 40 GeV
Data
σ
1
±
Background
= 2 TeV
Z'
Signal m
= 3 TeV
Z'
Signal m
ATLAS
-1
= 13TeV, 139 fb
s
γ
H
→
Z'
→
q
q
single b-tagged
(a)
1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
1
−
0
1
2
Significance
1000 1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
10
1
−
10
1
10
2
10
3
10
4
10
5
10
Events / 40 GeV
Data
σ
1
±
Background
= 2 TeV
Z'
Signal m
= 3 TeV
Z'
Signal m
ATLAS
-1
= 13TeV, 139 fb
s
γ
H
→
Z'
→
q
q
double b-tagged
(b)
1000 1500 2000 2500 3000 3500 4000
[GeV]
γ
J
m
2
−
1
−
0
1
2
Significance
Fig. 5.6 Distributions in the reconstructed H γ mass obtained by ATLAS from events with a
high- p T photon and an H -tagged jet. Events are categorised into H jets with a single b tag (left)
and a double b tag (right). The background is modelled by a parametric function with three free
parameters. Taken from [785]
5.2 Resonances Coupling to Third Generation Quarks
In certain BSM models, the couplings of heavy resonances to third generation quarks
is enhanced. This includes Kaluza-Klein excitations of gluons [39, 786] or gravitons [787, 788], massive colour-singlet W
and Z
bosons [789–793], colourons [794–
796], axigluons [797, 798], and pseudoscalar Higgs bosons [628, 679, 799]. In some
models of warped extra dimensions [699], resonance decays into bosons or third
generation quarks can be important, depending on the nature of the resonance and the
choice of free parameters [800]. For heavy neutral resonances, decays to bb would be
observable in dijet searches with b-tagged jets (see for example [801]), but decays to
tt result in distinct final states. Dedicated analyses are needed for optimal sensitivity,
reconstructing the tt system from its visible decay products. The decay of a narrow
resonance would be observable as a peak above the falling spectrum in the mass of
the tt system, m tt . Searches of this kind are probing the highest energy scales in tt
production, thus also testing our models used to simulate these final states. Charged
resonances would preferably decay to tb or its charge conjugate, if the couplings to
first and second generation quarks are suppressed. While also leptonic decays of the
kind W
→ ν are possible, these are forbidden for purely right-handed couplings of
the W
boson if the right-handed neutrino is heavier than a few GeV [802]. Similar
to tt resonance searches, a structure in the mass of the tb system is searched for.