Track reconstruction in the COSY11 Ushaped drift chamber

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Track reconstruction in the COSY-11 U-shaped
drift chamber

• Chamber construction
• Track reconstruction algorythm
• Calibration and reconstruction results

J. Smyrski, COSY-11 Meeting, Cracow, June 2004
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Drift chambers at COSY-11
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Chamber design
Drift cells
Section of end-plate
End-plate
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Chamber frame
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Reconstruction algorythm

• Finding track candidates in two dimensions
• independently for each orientation of wires
• Matching the two-dimensional solutions
• Three-dimensional fit

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Two-dimensional reconstruction

• Take all possible pairs of hits from two
  different planes
• Fit a straight-line
• Find hits consistent with the line

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Matching the two-dimensional solutions
h1 lt const
h2 lt const
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Three-dimensional fit
Parametrization of a track x-axis horizontal,
y-axis vertical z-axis perpendicular to
detection planes
Problem can be reduced to 3-dim. linear fit !
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Chamber calibration

• Calibration r (t, p, a),
• r distance to sense
  wire,
• t drift time,
• p - detection plane
  number,
• a - angular bin (00,
  900) /100.
• Iterative corrections to calibration
• ?r(t,p,a)ltrexp(t,p,a)gt - r(t,p,a),
• ltgt - average over a large number
• (gt105) of reconstructed tracks

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Reconstruction results

• Detection efficiency 100
• Reconstruction efficiency 97
• Pos. Resolution 150 ?m

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Cross-check with D1 and D2 chamber
a
b

• Straight-line parameters
• in horizontal plane
• in vertical plane

c
d
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To be done

• Tracking in the COSY-11 dipole field
• Publication in NIM