James Stirling

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The International Linear Collider an overview
of the physics motivation and theory

• James Stirling
• IPPP, University of Durham
• with acknowledgements to R Barbieri, J Ellis, D
  Miller (ICHEP04), M Peskin (Victoria LCW), S.
  Dawson, R. Heuer

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the most up-to-date reference
The LHC-LC Study Group Report Georg Weiglein et
al. www.ippp.dur.ac.uk/georg/lhclc/
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Particle Physics 2004
and beyond?
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Particle Physics 2004
and beyond?
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discrepancies?
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limits?
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the key questions
particle physics

1. What is the origin of mass? Is it the Higgs
   mechanism or ?
2. What is the origin of the matter-antimatter
   asymmetry in the universe?
3. What are the properties of neutrinos?
4. Is there unification of particles and forces
   including gravity?
5. What is the dark matter?

2) ? present and future B Factories 3) ? solar,
atmospheric, reactor, (super)beam, 0???, ,
NuFact experiments 1), 4), 5) ? high-energy
colliders Tevatron, LHC, ILC
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key issue electroweak symmetry breaking
Scenarios include

• Supersymmetry (MSSM and variants)
• Higgs as Pseudo Goldstone Boson
• Composite Higgs
• Technicolour
• Higgsless models
• Extra dimensions

Note in all scenarios, something (or some
combination of things) has to mimic a light Higgs
boson in the precision electroweak (EWPO) fits!
The Calculability Principle (Barbieri) Restrict
to models in which the Fermi scale (GF-1 or MZ)
can be related to some other physical scale (?NP
say) in a calculable manner, i.e. MZ ?NP f(ai)
where the ai are physical parameters. Then CP ?
consistency with data ? SUSY, Higgs as PGB
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what LHC can do SM-like Higgs
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what LHC can do SUSY
Higgses
sparticles
? whole plane covered for at least one Higgs (but
note large only h region!)
? squark and gluino masses eventually up to 2.5
TeV
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however

• hadro-philic bias in new physics searches
  (gg,qq ? X)
• large SM backgrounds always a problem (?Higgslt
  ?total ? 10-9)
• EWPO only modest improvement over Tevatron (mtop
  , mW )
• no longitudinal momentum balance missing pT
  for invisible particles is relatively crude tool
  quark flavour tagging difficult
• strong model dependence of new physics analyses

conventional SUSY neutrino LSP (Murayama et
al) bosonic supersymmetry (Cheng,
Matchev, Schmaltz)
multiple hypotheses, distinguished by different
spin and energy flows, difficult to distinguish
at LHC
Peskin (Victoria, 2004)
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cross sections LHC vs. ILC
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ILC physics summary

• whatever the scenario unveiled by Tevatron
  LHC, ILC has an essential role to play
• continue with precision electroweak measurements
  (in particular, mtop )
• if a light Higgs exists, measure its properties
  (mass, couplings to fermions gauge bosons,
  self-couplings, )
• if LHC reveals other light ( e.g. SUSY)
  particles, measure the spectrum and properties
• if LHC reveals no light particles, explore the 1
  TeV region through precision measurements
  sensitive to virtual new physics

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precision
MW cos?w MZ ? 1 a F(mt,MH,SUSY,..)
?mW (MeV) ?mtop (GeV) ?sin2?eff?105
now 34 3.9 17
TeV Run 2 16 1.4 29
LHC 15 1-2 14-20
ILC-GigaZ 7 0.1 1.3
Heinemeyer et al (LHCLC report)
Heinemeyer, Weiglein 04
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precision contd.
precision EW measurements complement direct new
physics measurements
Heinemeyer et al 2003
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Higgs physics at ILC

• Key questions
• precise mass?
• couplings to other particles SM or not?
• self-couplings?
• other higgses?

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Higgs physics at ILC

• Key questions
• precise mass?
• couplings to other particles SM or not?
• self-couplings?
• other higgses?

with
compare
Guasch, Hollik, Penaranda 2003
Example
also ttH coupling measurements see LHCLC report
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Higgs physics at ILC

• Key questions
• precise mass?
• couplings to other particles SM or not?
• self-couplings?
• other Higgses?

V(?) ½ mh2 ?2 ?3 v ?3 ¼ ?4 ?4
in SM ?3 ?4 ½ mh2 v-2
? ?3 / ?3 20
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supersymmetry at the ILC

• the task
• determination of kinematically accessible
  sparticle spectrum
• measure sparticle properties (masses, cross
  sections, JPC)
• use these (with complementary information from
  LHC) to constrain underlying SUSY model
• extrapolate to GUT scale using RGEs
• the techniques
• end point spectra
• threshold scans
• e-e-, e?, polarised beams

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example of a global MSSM spectrum fit




LSP





-
-



Needs gt 500 GeV. (Also lt 500 study in LHC/LC)
ee- threshold scan. - e-e- threshold scan
(s-wave allowed)
David Miller, ICHEP04
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the LHC-LC synergy using precisely measured LSP
mass at ILC to constrain LHC measurements of
slepton and squark masses
see e.g. LHCLC report for details, many more
examples, and references
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then on to the GUT scale!
Allanach, Blair, Kraml, Martyn, Polesello,
Porod,,Zerwas
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and if nothing below 500 GeV?
a generic feature of such models is heavy
s-channel resonances in the 1-3 TeV range (new
gauge bosons, technipions, KK resonances, )
little Higgs heavy Higgs no Higgs
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sensitivity to new heavy resonances in ee ???WW
sensitivity to new heavy Z
LC
LHC
M 1.9 TeV SM couplings (a1) LC 500 GeV, 500
pb-1
Richard 2003
Barklow et al, LHCLC report
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David Miller ICHEP04
Summary of the case for the TeV ILC
1. Definite ?mtlt100MeV

• If LHC sees nothing new
• below 500 GeV mass

Vital constraint. Increasingly sure it can be
done.
2. If there is a light Higgs
LHC probably sees. ILC shows what it is.
LHC and ILC needed to pin down model, identify
DM(?), extrapolate to GUT scale.
3. and extra particles