Track-based Alignment

Scope

Track-based alignment can be classified into three use cases:

• Alignment algorithms compute corrections to apply to the ideal positions of detector units, based on track residuals.

• Misalignment tools allow to misalign the detector with respect to ideal positions according to different scenarios, for later use in misalignment studies.

• User jobs, where the ideal geometry is corrected (in case of real data analysis), or misaligned (to study the effect of a misaligned detector on efficiency, fake rates, etc).

How-To

• Using the HIP alignment algorithm for tracker alignment
• Using the MillePede alignment algorithm for tracker alignment
• Using the alignment framework for muon chamber alignment
• Expert guide to misalignment tools
• More data related information or the tracker: TkAlignment (includes TIF How-tos, MC samples, etc.)

Versions

User jobs

Alignment corrections are applied by the geometry builders (TrackerGeometryBuilder, DTGeometryBuilder, CSCGeometryBuilder). Once the ideal geometry has been read, the alignment object is parsed and new positions and orientations are sequentially set to all detector units.

Please check the corresponding WorkBook entry for examples on how to apply alignment corrections in a normal job.

Alignments object

The alignment object Alignments is the database object provided by all alignment inputs (survey, laser, algorithms and misalignment scenarios). It contains a vector of AlignTransform of all the active detector units (i.e. those used by the reconstruction). The AlignTransform consists of the global position (3 coordinates) and global orientation (3 angles), as well as the global detector ID.

The alignment error object AlignmentErrors contains a vector of AlignTransformError corresponding to all the AlignTransform. An AlignTransformError is a symmetrical matrix. At present it only includes global errors on the position. Work is ongoing to make the errors local, as well as including errors on the angles.

The Alignment(Error)s vectors are ordered by increasing detector ID before storage to the database.

Derived alignment constants

• Run 3 alignment constants
• Run-II alignment constants
• Run-I alignment constants

Review Status

Responsible: AndreasMussgiller
Last reviewed by: Reviewer