Effects of magnet polarity on the alignment of the IT Stations

The study was triggered by on observation of small variations of the alignment constants between the opposite magnet polarities. For example, the observed changes of the Inner Tracker alignment constant between different magnet polarisations are for the x translation within 100 μm in for 2011 and within 200 μm for 2012. Moreover, a trend is visible where constants are shifted in the same direction for the Down polarity with regards to the Up one. The difference is significant because the spatial resolution of the Inner Tracker is about 50 μm. To investigate its origin the tests with different configurations and data files were performed.

Documentation

Talks

• Status of the Alignment in Magnetic Field 5/12/2013
• Status of the Alignment in Magnetic Field 23/1/2014
• Comparison of Alignment for different magnet polarities 20/02/2014
• Alignment differences with magnet polarity 20/03/2014
• Studies of Alignment with finer segmentation 24/04/2014
• Studies on Alignment vs time 15/05/2014
• Alignment with finer segmentation using J/ψ sample 26/6/2014
• Studies on tracker alignment 23/10/2014
• Tracker Alignment Studies 11/12/2014

Configuration files

The study of the alignment dependence on survey constraints was performed using different configuration sets:

Set1 - OT(3)CFrameLayers fixed in Tx and Tz using survey constraints, no survey constraints in Tx OTCFrames, OTModules allowed to move in Tx and Rz ( config_set1.py);

Set2 - OTCFrameLayers fixed in Tx and Tz using survey constraints, OTModules fixed with regards to OTCFrameLayers ( config_set2.py);

Set3 - OTCFrames and OTCFrameLayers fixed in Tx and Tz using survey constraints, OTModules allowed to move in Tx and Rz ( config_set3.py);

Set4 - OTCFrames and OTCFrameLayers fixed in Tx and Tz using survey constraints, OTModules fixed with regards to OTCFrameLayers ( config_set4.py);

Set5 -no survey constraints in Tx and Tz for OTCFrames and OTCFrameLayers, OTModules allowed to rotate around x axis (Rx) ( config_set5.py)

Input data

Alignment convergance test

For 2011 two periods with two magnet field polarities were considered for the convergence test.

Six periods were considered for 2012 year: two groups of consecutive periods with opposite magnetic field. For the first group the official alignment resulted in a large difference (up to 200 μm) for Tx alignment parameters. The other group exhibits small difference ~50 μm.

Time dependence of the alignment

Two periods with two magnet polarity were used. Each period was split on few subperiods.