First look at Z discovery potential in a bulk RandallSundrum model

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First look at Z discovery potential in a bulk
Randall-Sundrum model
Julien MOREL Fabienne LEDROIT Gregory
MOREAU ATLAS Exotics group LPSC - Grenoble
25 january 2007 Exotics meeting
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Introduction

• We already studied Z coming from Grand Unified
  Theories
• Using the CDDT parametrisation
• Discovery potential in TeV4LHC note
  (ATL-PHYS-PUB-2006-024)

• We are now interested in an extra dimension model
  
• A Randall Sundrum with matter in the bulk
• Z excluded up to 4 TeV
• We study Z in the ee- channel
• We need high luminosity ? 100 fb-1 ? not for the
  CSC note
• We use AtlFast simlation v12.0.4

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X-dim theory - Randall-Sundrum with bulk matter
G.Moreau, J. I. Silva-Marcos, hep-ph/0602155

• Gauge fields are in the bulk.
• Higgs field remains on the TeV brane.
• Fermions are in the bulk with different
  localizations along the extra-dimension.
• Z gauge coupling non universal
• Z mass is not predicted

TeV Brane (our 4D space)
Planck Brane

• 3 important features
• New interpretation of the fermion mass hierarchy.
• Compatible with a Grand Unified Theory
  hep-th/0108115 .
• KK excitation provides WIMP candidate.

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Parameters space points
We are interested in 3 points in agreement with
the EW constraint
Di-lepton invariant mass in the RS model
Interference
Resonance

• We can see 2 effects
• An excess of cross section due to a resonance
• A lower cross section due to a destructive
  interference

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The ATLAS detector efficiency

• To compute detector efficiency
• We fast simulate Zc from GUT up to 10 TeV
• (using official pythia JobOptions)
• Fast simulation of ZRS under investigation
• (using an external pythia process)

As the efficiency depend only on the parton
flavour, we can compute the discovery potential
of ZRS with the efficiency coming from Zc
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Minimal cross check with available samples
We fast simulate Zc in v12 because we have fully
simulated Zc in v11
Zc selection efficiency
Zc selection efficiency
FastSim v12.0.4 FullSim v11.0.41
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Z selection efficiency up to 10 TeV
We plug these efficiencies in our Pythia user
process for ZRS to compute the ATLAS discovery
potential
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ATLAS Discovery potential for a Z
To compute the Z ATLAS Discovery potential we
need

• The efficiency (e)
• The cross section
  (sZ) signal
• The DY cross section (sDY)
  main background
• A significance convention (S12)

We use the same strategy as for the TeV4LHC note.
Using an event counting method with the realistic
significance S12 propose in hep-ph/0204326
Asking 2S12 gt 5 for a discovery
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ZRS discovery potential
We calculate the significance S12 in two regions
of the mass spectrum

• In the resonance region
• Above M1
• In the interference region
• Between 500 GeV and M1

We chose M1 model-independent such that
M1 depends on the luminosity and corresponds to
the tail of the DY process.
M1
?15 events
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ZRS discovery potential for point B

• ATLAS can discover up to 3.8 TeV with 10 fb-1
  (already excluded)

• ATLAS can discover up to 5 TeV or 7 TeV with 100
  or 300 fb-1

• Interference effect seems to be more visible at
  high luminosity

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ZRS discovery potential for point A and C
Point A

• up to 6 TeV with 10 fb-1 with interference
  research

• up to 10 TeV with 100 fb-1 (via interefrence)

Point C

• up to 3 TeV with 10 fb-1 with resonance research

• up to 3.8 TeV with 100 fb-1 (via resonance)

• up to 4.5 TeV with 300 fb-1 (via interference)

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Outlook

• Cross check the Z acceptance with full
  simulation
• Compute acceptance with ZRS instead of Zc
• Compute the discovery potential in the mm-
  channel (ZRS couplings non-universal)
• Write a note