STEP propagator and tracking geometry at ATLAS

1
STEP propagator andtracking geometry at ATLAS

• Esben Lund, University of Oslo
• Andi Salzburger, CERN PH-ATC University of
  Innsbruck

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Why another propagator?

• To combine tracks from the inner detector and the
  muon chambers, propagation through the
  calorimeters is necessary.
• Material effects must be taken into account both
  for the track and the associated covariance
  matrix.
• The inhomogenous magnetic field at ATLAS requires
  special attention.

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The toroidal magnetic field
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Track parameters
Full set of track parameters
x1 x2 j q q/p
s1 c12 cl3 cl4 cl5
c21 s2 c23 c24 c25
c31 c32 s3 c34 c35
c41 c42 c43 s4 c45
c51 c52 c53 c54 s5
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Tracking geometry
Material interactions
Layer based
Volume based
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Simplified geometry
TrackingGeometry
GeoModel
Geant 4
associate material
to TrackingGeometry Layers
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Tracking software
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Runge-Kutta method
f2
f4
f3
f1
xi
xi h/2
xi h
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Relative propagation errors
STEP adaptive Runge-Kutta-Fehlberg
Runge-Kutta-Nystrøm
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Mean relative propagation errors
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Efficiencies
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Relative efficiencies