Small Extra Dimension Graviton Detection at ATLAS

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Small Extra Dimension Graviton Detection at ATLAS

• Looking at the Graviton as it decays through
  G-gtZ0 Z0 -gte-ee-e
• Audrey Todhunter
• Case Western Reserve University
• Dominik Dannheim
• Columbia University

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The Graviton

• Massive graviton resonances are predicted by
  models using extra dimensions
• -resonances could be well separated in mass
• The graviton couples universally
  (ee,??,??,??,Z0Z0, etc)
• -Products could be detected at ATLAS
• Analysis used the Randall-Sundrum model, which
  predicts the mass of the first resonance by
• mn xn(k/MPl)??
• We chose k/MPl0.01 to give resonances on the TeV
  scale

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• This analysis
• pp?G?Z0Z0?ee-ee-
• against a Standard Model background
• qq?Z0Z0?ee-ee-
• The branching ratio Br for Z0Z0?ee-ee- is only
  3.43.4 11.56 for this decay process

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Signal and Background Simulation

• -Pythia event generator
• -mass points at 300GeV, 500GeV, 700GeV, 1TeV, and
  1.5TeV, as well background processes around each
  point
• -want to know how well these signals can be
  detected at ATLAS? Geant4 used in a full
  simulation of the ATLAS reconstruction

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Properties of simulated signal and background
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Particle Selection

• We can identify electrons by their
  characteristics detected in the EM calorimeter
  and the central tracker
• Transverse energy eT gt 20 GeV
• Likelihood gt 0.9 being electron rather than pion
• 2ee- pairs in each entry
• - best combination of particles decided by
  comparing reconstructed Z0 mass to known Z0 mass
  (91.1GeV)

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Invariant Z0 mass from a 300GeV signal from
electron pairs closest to Z0 mass within each
interaction
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Graviton Reconstruction

• -electrons chosen for Z0 mass used to reconstruct
  invariant G mass
• -signal scaled for 100 fb-1 luminosity (1 year
  running at design luminosity)
• NEv (?Br) L
• imposing a weight factor on the number of
  simulated events

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Signal at 500GeV with a Gaussian fitsigma
parameter used to look at events within a mass
window of 3?
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Signal and background added and fit
withp0e(-(x-p1)2/2p2 2 p3e(p4xp5)
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Potential discovery of resonances from
G?Z0Z0?ee-ee- at ATLAS

• count number of signal and background events
  within the 3? window
• need to have Nsiggt5v (NBG) or Nsig gt 10 for a
  statistically significant signal
• number of events can be increased by raising
  luminosity

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Luminosity needed for Nsiggt5v (NBG) or Nsig gt 10
L100fb-1 one year running at design luminosity
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Conclusions

• -for the process G?Z0Z0?ee-ee- the upper mass
  limit is slightly below 700GeV
• -higher discovery potential at increased
  luminosity
• -other decay channels are possible for the
  graviton which may have higher upper limits for
  detection