Universidad Nacional de Colombia
Departamento de Física
Grupo de Física Teórica de Altas Energías
Z’ Production in 331 models
Fredy A. Ochoa and Roberto Martínez
II LAWHEP
São Miguel das Missões, Dec. 2007
Outlines
• Motivations
• Z’ Basics: Theoretical and experimental facts
• The 331 Model
• Z’ Production at Tevatron
• Z’ Production at LHC
• Conclusions and Prospects
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¿Why beyond SM?
• The mechanism for breaking the electroweak symmetries and
generating mass
• The unification of forces, including gravity.
• The conection to cosmology (Baryon asymmetry, Cold Dark Matter. )
• The mass hierarchy problem
• The existence of 3 families
• The electric charge quantization
• The neutrino masses and mixing
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Z’ Boson Basics: Theoretical Facts
• A Z’ particle is a neutral, spin-1, colorless and self-adjoint gauge boson
arising from some extensions of the SM, which is more massive than the
SM Z boson.
• Z’-models: +U(1) from E6, Left-Right, Little Higgs, Sequential SM, 331
• Z and Z’ bosons are not true mass eigenstates. The physical bosons are
mixing states Z1 and Z2 with a mixing angle q, which cause deviations from
the SM (Z-pole parameters, shifts in the W couplings, shifts in the Weak
Charge, F-B Asymmetries, etc.)
• The MZ’ is not constrained by the theory. It can be anywhere between
Eweak < MZ’ < EGUT.
• An observation of the Z’ would provide information on the GUT group
and on its symmetry breaking.
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Z’ Boson Basics: Experimental Facts
• A Z’ particle is a resonance, which is more massive than the SM Z,
observed in the Drell-Yan process pp(pp )
l l + X.
• A Z’ can be directly observed through its decay products. It is possible
in lepton collisions (ILC) or in hadron collisions (Tevatron, LHC).
• Present limits from direct production at Tevatron and virtual effects at
LEP through mixing with the Z boson, imply that MZ’ ~ TeV and Sq ~ 10. -3
• In hadron colliders, the sensitivity to Z’ production decaying into
quarks pairs is reduced compared to lepton pairs due to the QCD
background
• An observation of a Z’ would serve as a calibration point for future
detectors
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¿What is 331?
F. Pisano and V. Pleitez, Phys. Rev. D46, (1992) 410
P.H. Frampton, Phys. Rev. Lett. 69 (1992) 2889
3-3-1
SM
yL
yR
=
=
qL : (3, 2, 1/6)
lL : (1, 2, -1/2)
qR : (3, 1, 2/3)
lR : (1, 1, -1)
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yLL* ==
y
yR
(3,3,*3,Xq
Xq* ))
qqL*L::(3,
(1,3,*3,Xl
Xl* ))
llL*L::(1,
qR : (3, 1, Xq)
=
lR : (1, 1, Xl)
¿Why 331?
• From cancelation of Chiral Anomalies and asymptotic freedom, the
number of families should be 3
• The third family is different from the two first, which could explain
why the t and b quarks are so heavy (hierarchy problem)
• Predict the quantization of electric charge and the vector nature of EM.
• Contains a natural Peccei-Quinn symmetry
• New types of matter relevant at LHC
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Fermion Structure (3 flias.)
If b = -1/
QE = 0
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3:
EL = (nR) c
Neutral
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Neutral Currents
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Z’ at Tevatron
fq/A : PDFs,
Cross section for pp
GZ’ : Total Z’ width
s : C.M Energy
gv,a : Z’ couplings
y : rapidity
pz : long. momentum
E: total energy
q: Scattering angle
M = Mff : invariant mass
xA,B : momentum fractions
K(M) : QED and QCD
corrections
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Z’
ff
Z’ at Tevatron
2
At NWA aproximation: (GZ’/MZ’) << 1
Branching ratio
Total Z’ production
cross section
331 model with b = -1/ 3 :
2
( Gz’ / Mz’ ) ~ 4 x 10 - 4
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Z’ at Tevatron
Kinematics at CDF II
• pp collisions at C.M. energy
s = 1.96 TeV,
• Integrated Luminosity = 1.3 fb -1
• Azimuthally and F-B symmetric,
• Search for Z’ in the channel qq
Z’
e+ e -
• Events with invariant mass Mee > 200 GeV/c2
• Central Calorimeter with pseudorapidity h < 1.1
• Plug Calorimeter with pseudorapidity 1.2 < h < 3.6,
• Transverse energy ET > 25 GeV.
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Z’ at Tevatron
MZ’ > 920 GeV
Z’-models
95% C.L.
Bounds
Z’SM
923
Z’y
822
Z’h
891
Z’c
822
Z’331
920
331
(CalcHep Package)
T. Aaltonen et.al. (CDF Collaboration),
Phys. Rev. Lett. 99, (2007) 171802
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Z’ at LHC
Kinematics at ATLAS
• pp collisions at C.M. energy
s = 14 TeV,
• Integrated Luminosity = 100 fb -1
• Azimuthally and F-B symmetric,
• Search for Z’ in the channel qq
Z’
e+ e -
• Pseudorapidity h < 2.5
•Transverse energy ET > 20 GeV.
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Z’ at LHC
for Mz’ = 1500 GeV
N = s.L
Z’ at LHC
LHC Projections for 1 TeV < MZ’ < 5 TeV
Z’331
Z’LR
Z’c
Z’h
Z’Y
SM bkg
N = s.L
Conclusions
• For 331 model with b = -1/ 3, we get the limit Mz’331 > 920 GeV at
95% C.L in Tevatron
• For Mz’ = 1500 GeV, we get about 800 events for each 20 GeV of
energy with L = 100 fb at LHC
-1
• At Mz’ = 1 TeV we found ~ 10.000 events with low expected SM bcg
• The model pull the LHC dicovery potential up to 5 TeV, with 1 event
Prospects
• Calculations for other 331 models and other Mz’ limits
• Effects of exotic decay modes as fermions, charged heavy
bosons, higss, etc (smaller branching ratios)
• Effects on the lepton F-B Asymmetries
• Extension to ILC
Back
silides
Scalar Structure (3 tripletes)
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Vector Structure (9 campos)
8 Gauge Bosons
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1 Gauge Boson
Charged
Neutral
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