Search for extra gauge bosons in Little Higgs Models at a linear collider

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Search for extra gauge bosons in Little Higgs
Models at a linear collider

• Gi-Chol Cho
• (Ochanomizu Univ.)
• LCWS2004, Apr.21.2004
• in collaboration with Aya Omote

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Introduction

• Little Higgs Model alternative candidate to
  solve the hierarchy problem
• setup
• global symmetry
• local symmetry ( GSM)
• global/local symmetries are broken
  simultaneously
• Higgs boson ? pseudo Goldstone boson via global
  symmetry breaking
• extra particles acquire masses sym.breaking
  scale
• quadratic divergences of mh2 are cancelled
  _at_1-loop
• cut-off scale O(10TeV)

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Littlest Higgs Model (Arkani-Hamed etal.)

• a simplest structure
• global symmetry SU(5) ? SO(5)
• local symmetry SU(2)xU(1)1xSU(2)xU(1)2?GSM
• extra particles
• triplet Higgs
• vector-like quark (t)
• extra gauge bosons (AH, ZH, WH)

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Extra gauge bosons

• before symmetry breaking
• after symmetry breaking (SU(2)xU(1)1xSU(2)xU(1)
  2?GSM)
• W, B massive O(f) (decay constant of pseudo
  GS)
• EW sym. breaking
• charged states
• neutral states
• Free parameters

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Mass of extra neutral gauge bosons

• AH is relatively lighter than the other extra
  particles because of the hypercharge coupling
• could be as light as 1TeV in sizable parameter
  space

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• LHC has a detectability of TeV Z boson in some
  class of models
• What can LC do if LHC find a Z boson (lt 1TeV)?
• If Z mass is smaller than the CM energy of LC,
  it can be produced in s-channel
• Can LC tell us that if discovered Z boson is in
  Littlest Higgs model or SUSY E6 models?

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• focus at the resonance of Z
• high statistics
• reduce number of parameters

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Z bosons in SUSY E6 models
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Z-f-f couplings
and extra fields to make a complete multiplet of
E6
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peak cross section

• AH gives a few times larger cross section than Z
  in E6 models
• couplings of depend on

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• cross section (AH) decreases rapidly at
• ? comparable to the other models
• ? hard to distinguish

m500GeV
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Forward-backward asymmetry

• asymmetry in LHM depends charges only (not mixing
  angles)

• ratio of left- and right-handed charges to Z
  boson determine the asymmetry

parameter rf does not depend on
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FB asymmetry
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why AcFB0?
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• E6 models extra U(1) charges of quarks/leptons
  in rep. of SU(5) are common
• (uL, uR) belong to the 10 rep. of SU(5) ? no
  asymmetry!

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beyond E6?

• deviation of eL, eR charges from little higgs
  model
• cross section 10-100pb, lt O(1) measurement may
  be possible
• 10 deviation of the couplings can be measured?

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Summary

• possibility to distinguish Z boson in Littlest
  Higgs model and SUSY-E6 models are studied (after
  Z discovery at LHC)
• peak cross section of in
  Littlest Higgs models is sizably larger than E6
  models in most of parameter space, but becomes
  comparable when
• for b-, c-quarks are useful for our
  purpose because it is independent of
• in E6 models because of the
  SU(5) symmetry, while it is 0.4 in Littlest Higgs
  model ? clear signal?