Electroweak Symmetry Breaking without Higgs Bosons in ATLAS

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Electroweak Symmetry Breaking without Higgs
Bosons in ATLAS
Ryuichi Takashima Kyoto University of
Education For the ATLAS Collaboration
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Outline

• Possible scenarios of EWSB
• Little Higgs Model
• Chiral Lagrangian model
• Performance studies on boson scattering
• Summary

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Electroweak Symmetry Breaking (EWSB)
Extended Gauge Symmetry Little Higgs, Higgsless,
Left-Right Symmetric Model Higgs-Gauge Unification
J.Lykken, Physics at LHC (Vienna)
SUSY (m)SUGRA GMSB AMSB Mirage Split SUSY RPV
Extra-Dimension LED(ADD) Randall-Sundrum Universa
l ED(KK)
Precision EW data
Dynamical Symmetry Breaking Strong EWSB, Chiral
Lagrangian, Technicolor, Composite Higgs,
Top-quark Condensation
Exotics Compositeness, Lepto-quarks, Monopole
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EWSB possible scenarios

• ElectroWeak Symmetry Breaking (EWSB)
• ElectroWeak Gauge symmetry requires gauge boson
  and matter particles to be massless. The
  mechanism to give them mass Standard theory of
  EWSB by scalar Higgs field
• Renormalization scheme predicts coupling
  constants of Strong and EW force become same
  value near ? 1016 GeV Suggest GUTs of SU(3)C ?
  SU(2)L ? U(1)Y forces
• Higgs radiative correction mass2 has a quadratic
  term of cutoff parameter. Hierarchy problem in
  GUTs.
• If Higgs ? hierarchy problem fine tuning in rad
  corr to Higgs masssolution new physics at TeV
  scale (SUSY, Little Higgs, etc)
• If NO Higgssolution dynamical symmetry breaking
  (Technicolor, Chiral Lagrangian etc)
• Unitarity violation in longitudinal WW scattering
  at high Esolution Higgs boson or other new
  particle with mass lt 1 TeV

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Little Higgs Model

• Evaluate the sensitivity to the Little Higgs
  models with the ATLAS experiment
• at the LHC
• Little Higgs Models proposed as a solution to the
  Hierarchy problem
• Loop corrections to the Higgs Mass L is an
  ultra-violet cut-off
• Models try to arrange new particles to cancel
  these effects
• Little Higgs models add a minimal set of
  particles (and a symmetry) to cancel these
• corrections up to Lgt10TeV
• Some discussion on T-parity of heavy top and
  bosons. Require pair production.

To suppress the quadratic divergence the mass of
MT and MW should not be too large
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Little Higgs heavy top search

• Production via QCD (gg ? T Tbar, qq ? T
  Tbar) via W exchange (qb ? q T)
• dominant for MT gt
  700 GeV
• Decays T ? t Z, T ? t h, T ? b W
• cleanest is T ? t Z ? b l ? l l-but small
  statistics, main bkg is tbZ5? signal up to
  1.0-1.4 TeV
• T ? t h ? b l n b bbar lt 5s
• T ? b W ? b l ?main bkg is t tbar5? signal up
  to 2.0-2.5 TeV

SN-ATLAS-2004-038
M 1 TeV 300 fb-1
bkg
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Little Higgs heavy bosons
SN-ATLAS-2004-038
300 fb-1

• AH, WH and ZH discovery in lepton modesup to M
  6 TeV (depending on param cot q)
• Discrimination against other modelspredicting
  dilepton resonances via observation of decay
  modeslike WH ? W h, ZH ? Z h, and WH ? t b
  (important at cot q 1)

5s discovery
ATL-PHYS-PUB-2006-003
300 fb-1
M 1 TeV cot ? 1 30 fb-1
WH ? t b observation up to 3 TeV
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Symmetry Breaking by Chiral Lagrangian Model

• SM cross section for Wlong Wlong scattering
  diverges at high energy if there is no Higgs ?
  new physics via diboson resonances?
• Chiral Lagrangian Model
• Describes the low energy effects of different
  strongly interacting models of the EWSB sector.
• The differences among underlying theories appear
  through the values of the effective chiral
  couplings.
• The analytical complete form can be found in
  Dobado et al., Phys.Rev.D62,055011, but terms of
  major importance are

• Different choices for the magnitude and the sign
  of a4 and a5 would correspond to
• different choices for the underlying (unknown)
  theory.

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Performance studies on boson scattering

• WLWL with no resonances (Continuum) by J.M.
  Butterworth, P. Sherwood, S. Stefanidis.
• WLWL with resonances by S.E. Allwood, J.M.
  Butterworth, B.E. Cox.
• WLZL with resonances by G. Azuelos, P-A. Delsart,
  J. Idarraga, A. Myagkov.
• PYTHIA has been modified to include the EWChL and
  to produce the resonances for different
  parameters.
• Detector response was studied using Athena
  computing environment of both fast and full
  simulators.

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WW Boson Scattering
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WW Boson Scattering Event Selection

• high pT lepton
• high ETmiss
• Jet(s) with high pT and m mW.
• Little hadronic activity in the central region
  (?lt2.5) apart from the hadronic W.
• Tag jets at large ? (?gt2).

high pT W

• Backgrounds Wjets (W ? l?), s60,000 fb, and
  , s16,000 fb ttbar
• (cf signal slt100 fb).

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Resonant WW Boson Scattering
preliminary
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Resonant WZ Boson Scattering

• choose parameters of a4 and a5 such that new
  resonance M 1.15 TeV
• qq ? qqWZ ? qq ln ll (s x BR 1.3 fb)
• qq ? qqWZ ? qq jj ll (s x BR 4.1 fb)
• qq ? qqWZ ? qq ln jj (s x BR 14 fb)

Lq.Ar FCAL hlt4.9
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Resonant WZ Boson Scattering

• Selection for qqjjll 2 forward jets central
  2jets and 2 leptons Require no
  additional central jet
• Bkg gluon and g/Z exchange with W and Z
  radiation also t tbar W4 jets (need more
  stats)
• Experimental issues
• Merging of jets from high-pTW or Z decay (need
  cone DR 0.2)
• Impact of pileup on forwardjet tagging?
• Promising sensitivity for jet modes at 100 fb-1
  (need 300 fb-1 for WZ ? ln ll)? study is ongoing

SMbg
ATL-COM-PHYS-2006-041
100 fb-1
W Z ? jj ll
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Summary

• Many scenarios for EWSB being studied.
• Heavy Top is reachable. WH ? t b hadronic decay
  channel can be used to discriminate the Little
  Higgs model from other models.
• WZ boson scattering is studied extensively.
  Promising mode to test the dynamical symmetry
  breaking and various models including higgsless
  model.
• Atlas can explore the parameter space of Chiral
  Lagrangian model by WW scattering with 30 fb-1
  data.

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References

• G. Azuelos P. A. Delsart J. Idarraga A.
  Myagkov ,ATL-COM-PHYS-2006-041
• S.Willocq,http//ichep06.jinr.ru/reports/150_11s5_
  15p10_willocq.ppt
• S.Stephanidis,http//indico.cern.ch/conferenceOthe
  rViews.py? viewstandardconfIda0572006-07-06
• F. Ledroit,http//susy06.physics.uci.edu/talks/1/l
  edroit.pdf
• S. González de la Hoz L. March E.
  Ros,ATL-COM-PHYS-2005-001
• G. Azuelos et al, SN-ATLAS-2004-038