Post on 18-Feb-2019
T-odd quarksin the Littlest Higgs model
Giacomo CacciapagliaIPNL
15 April 2010MC4BSM
Niels Bohr Institute, København
arXiv:0911:4630, with S.Rai Choudhury, A.Deandrea, N.Gaur and M.Klasen
The model
Stabilisation of the EW scale: Higgs as a Pseudo-Goldstone boson
Global symmetry G broken to subgroup H at a scale f (Λ = 4πf)
Higgs part of the coset G/H
Gauged subgroup contains SM gauge groups
Quadratic divergences cancelled at one loop by same spin particles!
The model: Littlest Higgs
G = SU(5) broken to H = SO(5)
Gauged 2X [SU(2) x U(1) ] → SU(1)L xU(1)Y
24-10=14 Nambu-Goldstone bosons: Heavy gauge bosons (4) + H (4) + heavy triplet φ (6)
Many new states: AH , WH , ZH , φ; mass O(f)
Tree level corrections to EWPTs: f > few TeV! The naturalness problem is reintroduced!
The model: Littlest Higgswith T-parity
To avoid EWP bounds, I.Low proposed a discrete parity (T-parity) that exchanges the two SU(2)xU(1) gauged groups
W = W1+W2 even; WH = W1-W2 odd!
Requires T-odd partner for all fermions: QH and LH!
bound (loops) softened to f > 500 GeV!
AH plays the role of dark matter candidate.
Vector masses:
Fermion masses (κ = Yukawa coupling, κ < 3.5 f/TeV, flavour blind and universal):
Numerically:
The model: Littlest Higgswith T-parity
Branching ratios
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
BR
(DH
)
!
WH UZH DAH D
0
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 1
BR
(UH
)
!
WH DZH UAH U
For κ ≥ 0.46, QH→WH q→AH Wq→AH lνq→ l jet MET60% 100% 21%
Chain branching ratio: 12%
Production cross sections
Only strong production from gluons and quark annihilation
Dominated by s-channel diagrams (fall-off rapidly with s)
Only opposite sign dilepton signatures
In previous work, i.e. Freitas/Wyler and Choudhuri/Gosh:
Production cross sections
We consider both strong and weak processes
Weak t-channel (heavy gauge bosons) give a large contribution in the forward region (exp. at large κ)
We included corrections to the vertices
We included NLO k-factors for both signal and background
In our work:
Opposite sign dilepton ⇒
Same sign dilepton ⇒
pp→QH QH (QCD+EW)pp→UH DH (EW)
_
pp→UH DH + UH DH (EW)_ _
v2
f2
Belyaev, Chen, Tobe, Yuan
Production cross sections @ 14TeV
0.01
0.1
1
10
100
1000
10000
100000
400 600 800 1000 1200 1400 1600 1800 2000
! (
fb)
f (GeV)
"!= 1
Old resultOld + EW
Same sign leptons
1
10
100
1000
10000
100000
400 600 800 1000 1200 1400 1600 1800 2000
! (
fb)
f (GeV)
"!= 0.6
Old resultOld + EW
Same sign leptons
1e-05
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
400 600 800 1000 1200 1400 1600 1800 2000
! (
fb)
f (GeV)
"!= 1.5
Old resultOld + EW
Same sign leptons
RED: only QCD (Choudhuri et al)BLACK: QCD+EW oposite-sign processesBLUE: EW same-sign processes
Note: EW more impfor large κ
Our simulation:3 benchmark points
Signal generated with CalcHEP 2.5.4 + PYTHIA 6.4.21CalcHEP model files can be found in
http://deandrea.home.cern.ch/deandrea/LHTmodl.tgz
Opposite sign leptons: backgrounds
t tbar, with both tops decaying leptonically and bottoms misidentified for light jets
WWjj, with both W decaying leptonically
ZZjj, with one Z decaying leptonically and the other invisible
two leptons with pt > 15 GeV and η < 2.5
b-jet veto, with a b-tagging accuracy of 60%
two light jets with pt > 30 GeV and η < 2.5
MET > 30 GeV
dilepton invariant mass > 15 GeV
and cuts:
PYTHIA 6.4.21
⇐ suppress t tbar
⇐ suppress photons
Same-sign leptons
(GeV)TE
0 200 400 600 800 1000 1200 1400
# o
f ev
ents
/ 1
5 G
eV
1
10
210
310
410
(GeV)TE
0 200 400 600 800 1000 1200 1400
# o
f ev
ents
/ 1
5 G
eV
1
10
210
310
410
10)! = 0.6 (!f = 1000 GeV,
10)! = 1.5 (!f = 700 GeV,
10)! = 1 (!f = 1000 GeV,
tt
W W jj
Z Z jj
(GeV)TH
0 500 1000 1500 2000 2500 3000 3500 4000
# o
f ev
ents
/ 4
0 G
eV10
210
310
410
(GeV)TH
0 500 1000 1500 2000 2500 3000 3500 4000
# o
f ev
ents
/ 4
0 G
eV10
210
310
410
10)! = 0.6 (!f = 1000 GeV,
10)! = 1.5 (!f = 700 GeV,
10)! = 1 (!f = 1000 GeV,
tt
W W jj
Z Z jj
ATLFASTLuminosity 100 fb-1
Naveen Gaur
Same-sign leptons
(GeV)TE
0 200 400 600 800 1000 1200 1400
# o
f ev
ents
/ 1
5 G
eV
1
10
210
310
410
(GeV)TE
0 200 400 600 800 1000 1200 1400
# o
f ev
ents
/ 1
5 G
eV
1
10
210
310
410
10)! = 0.6 (!f = 1000 GeV,
10)! = 1.5 (!f = 700 GeV,
10)! = 1 (!f = 1000 GeV,
tt
W W jj
Z Z jj
(GeV)TH
0 500 1000 1500 2000 2500 3000 3500 4000
# o
f ev
ents
/ 4
0 G
eV10
210
310
410
(GeV)TH
0 500 1000 1500 2000 2500 3000 3500 4000
# o
f ev
ents
/ 4
0 G
eV10
210
310
410
10)! = 0.6 (!f = 1000 GeV,
10)! = 1.5 (!f = 700 GeV,
10)! = 1 (!f = 1000 GeV,
tt
W W jj
Z Z jj
ATLFASTLuminosity 100 fb-1
Naveen Gaur
Opposite-sign leptons
(GeV)TE
0 200 400 600 800 1000 1200
# o
f ev
ents
/ 1
5 G
eV
0
20
40
60
80
100
120
(GeV)TE
0 200 400 600 800 1000 1200
# o
f ev
ents
/ 1
5 G
eV
0
20
40
60
80
100
120 5)! = 0.6 (!f = 1000 GeV,
5)! = 1.5 (!f = 700 GeV,
5)! = 1 (!f = 1000 GeV,
W W jj
W W W
(GeV)TH
0 500 1000 1500 2000 2500 3000 3500 4000
# o
f ev
ents
/ 4
0 G
eV
0
10
20
30
40
50
60
70
(GeV)TH
0 500 1000 1500 2000 2500 3000 3500 4000
# o
f ev
ents
/ 4
0 G
eV
0
10
20
30
40
50
60
70 5)! = 0.6 (!f = 1000 GeV,
5)! = 1.5 (!f = 700 GeV,
5)! = 1 (!f = 1000 GeV,
W W jj
W W W
ATLFASTLuminosity 100 fb-1
Naveen Gaur
T-odd Leptons: 2 lepton signal
0.01
0.1
1
10
100
1000
400 600 800 1000 1200 1400
! (
fb)
f (GeV)
"l = 0.3, #s = 14 TeV"l = 0.5, #s = 14 TeV"l = 0.7, #s = 14 TeV"l = 0.3, #s = 10 TeV"l = 0.5, #s = 10 TeV"l = 0.7, #s = 10 TeV
(GeV)TE
0 50 100 150 200 250 300 350 400 450 500
# o
f ev
ents
/ 5
GeV
1
10
210
310
410 = 0.4l!f = 500 GeV,
= 0.35l!f = 700 GeV,
= 0.45l!f = 600 GeV,
ZZ
WW
pp -> lH lH
lH -> AH l @ 100%
Conclusion
Light quark (and lepton) partner are a necessary ingredient in Little Higgs models with T-parity
We show that the EW interactions give an important (previously ignored) contribution to the production cross section
Opposite-sign and same-sign dilepton signatures offer a good discovery channel for quarks at large luminosities (L = 100 fb-1)
single lepton and dilepton are discovery channels at low luminosity for leptons
The model: Littlest Higgswith T-parity
To avoid EWP bounds, I.Low proposed a discrete parity (T-parity) that exchanges the two SU(2)xU(1) gauged groups
W = W1+W2 even; WH = W1-W2 odd!
Requires T-odd partner for all fermions: QH and LH!
bound (loops) softened to f > 500 GeV!
AH plays the role of dark matter candidate:
from Hubitz and Meade
Same sign leptons: backgrounds and cuts
WWW, with same sign Ws decaying leptonically and the other in jets
WWjj, with same sign Ws decaying leptonically
two same sign leptons with pt > 15 GeV and η < 2.5
two light jets with pt > 30 GeV and η < 2.5
MET > 30 GeV
Cuts:
One lepton: backgrounds and cuts
on-shell W, decaying leptonically
WZ, with W decaying leptonically and Z invisibly (neutrinos)
one isolated lepton with pt > 10 GeV and η < 3
jet veto, with pt > 30 GeV and η < 3
Cuts: