In the L1 trigger after 2D vertexes have been found and for all tracks in HLT and offline the phi information will be added to the tracks.

The phi sensors are laid out as below in There are 683 strip in the inner region and 1365 in the outer region.

The strips are skewed from true phi to allow a slight stereo angle. The stations are also fitted alternating with R upstream or downstream which reverses the stereo angle in alternating stations. Which means until the radius of a hit can be estimated phi is not known.

Tracks from near the beam axis are expected to have roughly equal phi values.

  1. Tracks are sorted by length with the longest tracks taken first
  2. For each 2D track the radius at last two stations with R clusters is calculated
  3. The actual phi of the "phi" clusters is estimated using the projected radius.
  4. Pairs of phi hits are compared and those with close enough in phi are added to the track and a 3D trajectory constructed.
  5. The track is projected backward and forward and phi hits, corrected for R of the extrapolation, are added if close enough

Tracks are then stored to be converted to tracks used in fitting later.

-- DavidHutchcroft - 09 Aug 2005

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Postscriptps r1 manage 20.8 K 2005-08-09 - 11:43 DavidHutchcroft PR04 Phi strip layout
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Topic revision: r2 - 2005-08-12 - DavidHutchcroft
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