Looking for the Observable SUSY Channel at ATLAS ATLAS Physics Workshop at JINR 14 April 2006 JINR Dubna

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Looking for the Observable SUSY Channel at ATLAS
ATLAS Physics Workshop at JINR 14 April
2006JINR Dubna

• Presented by
• Gia Khoriauli
• (On leave from TSU, Georgia)
• Authors
• V. Bedniakov, Y.Budagov, A. Gladyshev, D.
  Kazakov, G. Khoriauli, J.Khubua

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SuperSymmetry (SUSY)

• SUSY is the theory about a symmetry between
  bosons and fermions and it is the mostly
  believed/expected candidate theory for Grand
  Unification.
• Motivations for SUSY
• It is locally invariance gauge theory and
  therefore Gravitation can be included by the
  natural way
• Unification of gauge coupling constants into an
  universal one at very high energies (1015 1016
  GeV) , what is not possible within Standard Model
• It solves the problem of hierarchy and vanishes
  radiation corrections to boson masses, which are
  very big at large energy scale because of the
  contribution of very massive particle loops
• Radiation breaking of electro-weak symmetry. This
  spontaneous symmetry breaking is naturally caused
  by radiation corrections to the mass parameters
  of Higgs potential
• SUSY lightest neutral stable particle is good
  candidate for Dark Matter in the Universe

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Minimal SuperSymmetry Model (MSSM)

• In MSSM with using universality principle for all
  boson and fermions masses we can significantly
  reduce the number of free SUSY parameters. This
  model is called mSUGRA minimal supergravity.
  Free parameters are
• m0 - universal mass for all bosons
• m1/2 - universal mass for all fermions
• A - parameter of soft supersymmetry breaking
• sign(µ) sign of mixing parameter of two Higgs
  fields
• tanß ratio of vacuum expectation values of
  Higgs fields
• Plot on the right shows the mass parameters space
  with excluded regions (red and yellow dotted
  areas) due to the different experimental
  restrictions

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gg -gt gg in ATLAS

• Cross-section of 2gluons -gt 2gluino for s1/214
  TeV is estimated to be of the order of 10-12 barn
  1 pb
• We selected the following values for free
  parameters (Fixed point region in allowed
  parameter space)
• m0 1400 GeV
• m1/2 180 GeV
• A 0
• sign(µ) 1
• tanß 30
• In this case gluino has large branching ratio for
  the decay mode shown on the right diagram giving
  2 b-jets 2 muons large missed transverse
  energy. This channel has quite good signature in
  SUSY searching.
• For event generation we used Pythia generator
  within ATHENA framework

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gg -gt gg gt 4 b-jets 4 muons Etmiss

• The physical picture of the previous diagram is
  shown on the right plot. It is assumed that both
  initial gluons had Pt 0 and all beam remnants
  fly along the beam axis (z) . In this case, using
  the below formula we can calculate total missed
  transverse momentum, which is an observable
  quantity in an experiment
• However, very often the initial gluons Pt is not
  zero (see the plot on the next slide) and for
  full kinematics one should consider Pt of other
  particles and jets

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Pttot and Etmiss (Pythia)

• Down plot shows distribution of Etmiss for the
  events when initial Pttot of gg system was in the
  range (-?Pt , ?Pt) , where ?Pt 10 GeV

• Upper plot shows distribution of total Pt.
  Different from zero values correspond to the
  cases when one or both gluons in total had Pt ? 0

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Pt of ?01 and µ-µ pair , Radius of B-meson
decay vertex (Pythia)
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SM Background

• Right plot shows the diagram for main Standard
  Model background process to the SUSY process
  discussed above
• In this process there are also 4 b-jets and 4
  muons, but Etmiss is expected to be far less than
  it is in SUSY case
• We are currently in studying of background
  processes

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To do

• To study the dependence of the received results
  on the variation of SUSY free parameter values at
  generator level
• To continue a study of background processes at
  generator (Phytia, ) level and the comparison
  with the interesting SUSY process
• and main task to simulate, reconstruct and
  analyze this SUSY process within the ATLAS
  detector