New Physics at the LHC in the first year

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New Physics at the LHC in the first year
Orin Harris UW Physics Grad Student
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Talk Outline

• The LHC Enormous Potential
• New Physics
• New Gauge Boson(s)
• SM Higgs Particle
• SUSY Particles
• Summary

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The LHC Enormous Potential

• Design Luminosity Should reach 100 fb-1 per year
  after 3 years of operation.
• Initial Luminosity 10 fb-1 in the first year
  (10x Tevatron)
• Energy 14 TeV (7x Tevatron)
• Only 1 day at 1 design luminsoty would produce
  8000 t quarks, 100 QCD Jets beyond kinematic
  limit of Tevatron

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New Gauge Boson(s)

• New massive electrically neutral Gauge Bosons Z
  are a common feature in most extensions of the SM
  gauge group. They also arise in theories
  postulating extra dimensions.
• Dominant decay channels Z? ee-, µµ-, jj
• Discovery potential as a function of mz depends
  on how strongly Z couples to quarks/leptons
  compared to Z, ie how ?(Z) and BR(Z?) compares
  to ?(Z) and BR(Z?).

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Z ? ee-, ??-, jj
If the Zs BR into leptons is similar to Zs, can
expect about 10 events for an integrated
luminosity as low as 300 pb-1 (3 days _at_ initial
luminosity) for a particle mass of 1.5 TeV
100 fb-1
Shown is the ratio of coupling strengths, as a
fucntion of mZ needed for a 5? confidence level
signal
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Signal will be resonant peak on top of smooth
Drell-Yan background. Should be very clear signal
if ECAL response understood to a few
100 fb-1
(SM-like)
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SM Higgs ParticleThe last undetected particle
predicted by SM

• Discovery potential depends highly on the Higgs
  mass
• SM perturbative validity mH lt 1 TeV
• LEP program 114 GeV lt mH lt 186 GeV, with 95
  confidence
• For any assumed value of mH, SM predicts Higgs
  production cross-section and relative rate of
  various decay channels

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Dominant Higgs Production mechanisms and Cross
Sections
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Low mass region mH lt 130 GeV

• Dominant Channel H ? has large cross section
  BR 90, but a prohibitve QCD 2-jet background.
• Background too high for direct -fusion
  production channel. Must resort to observing
  leptonic decays for triggering from the
  associated production with W or Z boson or
  pair
• Requires excellent b-tagging, HCAL performance,
  and jet reconstruction probably not realistic in
  first year

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H ? ??

• H ? ?? is a rare decay channel BR10-3
• large background S/B 120.
• Demands excellent ECAL performance, angular
  resolution
• to observe the narrow mass peak above ??
  background

Expected signal for mH 120 GeV with 100 fb-1
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Outlook much better for larger Higgs mass 130
GeV lt mH lt 180 GeV

• Most promising channel H ? ZZ ? 4l until 180
  Gev when H ? ZZ ? 4l channel opens up
• Requires good identification, reconstruction, and
  measurement of high pT leptons, in each (4e,
  2e2?, 4?) decay channel.
• Detector performance should be good enough to
  ensure high significance discovery in this mass
  range in a year or two

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4? channel (muon spectrometer)
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180 GeV lt mH lt 800 GeV

• Dominant channel H ? ZZ ? 4l
• Background lt Signal
• Detector performance not crucial
• Signal broadens at high mass. In the unlikely
  case mH gt 800 GeV, the more difficult ZZ ? ll??,
  lljj, and WW ? l?jj decay modes cover that rest
  of the mass range

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Overall Sensitivity to SM Higgs Theoretically
(but not realistically) entire Higgs mass range
accesible at LHC in first year
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SUSY ParticlesSolves Hierarchy Problem,
candidate for dark matter

• Expect huge squark and gluino production cross
  sections, even for masses as large as a few TeV
• If R-parity is conserved (no proton decay), clear
  model-independent signature of several high-pT
  jets and large Etmiss
• But reliable reconstruction of Etmiss events is
  crucial
• And unlike Higgs, SUSY complicated by many free
  parameters.
• The best we can do is investigate in detail the
  signatures for particular points in the parameter
  space

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Constraining SUSY

• But even the most minimal SUSY extension of the
  SM (MSSM) has 105 new parameters. The space of
  free parameters is too large to meaningfully
  compare predictions with data.
• The most minimal gravity-mediated or
  gauge-mediated SUSY-breaking extensions of MSSM
  reduce the number of free parameters to 5 and 6,
  respectively.

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The minimal supergravity (mSUGRA) extension

• mSUGRA assumes that at the GUT scale all scalars
  have a common mass m0, all gauginos and Higgsinos
  have a common mass m1/2 (there are 3 other free
  parameters also)
• Though probably overly constraining, this model
  has a small enough parameter space that its
  predicted signatures can be studied with some
  thoroughness

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One point in the parameter space
5? isolines for squarks and gluinos, parametrized
in terms of m0 and m1/2, as a function of
integrated luminosity
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Another point (A0 300, tan? 2.1, ? gt 0)
More recent matrix-element techniques predict
higher backgrounds in this region (up to yellow
line)
meff ? Etmiss PT,1 PT,2 PT,3 PT,4
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In Summary

• If a Z of a few TeV exists whose BR into leptons
  is near Zs, it will be discovered in first year
• SM Higgs gt 180 GeV will likely produce a
  significant signal in the first year, but current
  data suggests SM Higgs lt 186 Gev
• Squarks and Gluinos up to a few TeV could
  produce a convincing signal in first year

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References

• ATLAS TDR pp673-952
• azrXiv hep-ph/050422 v1 25 Apr 2005
• LHC physics the first one-two years(s),
  Gianotti and Mangano