Alignment and database
/afs/cern.ch/user/w/wmurray/public/tb95/db contains alignement files.
e.g. 32.align. The name of the file is the run number from
which it was derived. Subroutine STALIF , which is called
by the DST program, looks for an alignment file with the
current run number, and if it does not find one it searches back until it does.
The alignment is found from the ntuple-DST. First the leftmost telescope module
is defined as perfect. Then the rightmost is aligned relative to it in D0 and
phi, using a measured z distance, such that the beam is as flat and as narrow
as possible.
After that the other telescope modules and test detectors are aligned to tracks
defined in the outer two modules using a chi-squared minimization. This is done
using MINUIT , and extrpolating the track to the detector many
times.
The parameters of the alignment file are:
- INUM - The module number
- ICOD - The code (VIKING, ADAM ETC.)
- IXYF - Is this an x or a y measurment (some modules do both)
- D0 - Distance of closest approach of strip one to the z axis, cm.
- Z0 - Z at this point, in cm
- PH - The phi angle of the strip, radians
- TH - The theta angle of the silicon (rotation about a strip)
- ETA - The eta angle of the strip (dip angle, radians)
- PITCH - The pitch of the detector
- YOF - The distance from the point of closest approach to the bottom edge
of the detector.
- DPDY - The change of pitch with y local, for Keystone detectors.
D0, Z0, PH, TH and ETA are all fitted; PITCH and DPDY are assumed. YOF is
ignored for parallel strip detectors and fitted for Keystone ones.
This scheme assumes only one peice of silicon on a readout line. It will need
modification.
Use of Alignment
See the tracking section.
- STGLLO Goes from global coordinates of a track to an x-local on a module.
It should be improved to give the y local too.
- STLOGL Goes from x local to a line in global coordinates on which the hit
lies. Probably not as useful.
Comments to :
Bill Murray