Global Alignments
Offline 1

Offline, the Central Arms (CA) are assumed to be unmovable, and define the Phenix global coordinate system.

Using CA tracks, the VTX aligns itself to the CA, so the VTX center is at (x,y,z)VTX. Internally, ladders are shifted after self-alignment.
Offline 2

The VTX finds where the beam is at (x,y)beam ( run-by-run??? ) relative to itself (and thereby relative to Phenix global (0,0,0).
Offline 3

The FVTX does its internal alignment, and aligns itself to the VTX.
Offline 4

Comparing FVTX and Muon arm tracks, an (x0mu,y0mu) offset is observed. that is, the Muon arm is offset from (0,0,0). Internally, however, the Mu arms are also unmovable. So muon coordinates (tracks) have to be shifted by (-x0mu,-y0mu) before being used by the FVTX/VTX/CA.
Monte Carlo

In Pisa,
  1. the Central arms are defined at (0,0,0)
  2. The VTX also sits at (0,0,0)
  3. the VTX internally has the ideal configuration
  4. the FVTX sits at its 'real' location relative to the VTX
  5. the FVTX internally is the same as the offline configuration
  6. the Muon arms are in the ideal location


So if we throw an event at (x,y)beam, tracks end up
  1. in the proper place in the Central Arms.
  2. in the wrong place in the VTX/FVTX
  3. in the wrong place in the Muon arms
Hubert Van Hecke
Last modified: Tue Jan 28 17:03:06 MST 2014