Tpc alignment with Cosmic for Run X/XI

 Processing of Cosmic for alignment has not yet been completed but I would like to share preliminary results on Inner to Outer sector misalignment. The method is following:

  • For tracks reconstructed
    • in one super sector
    • with more than 30 fit points in total and
    • more than 7 points in inner sector and
    • more that 19 point in outer one  
    • these hits are refitted by helix separately for inner and outer  hits.
  • The prediction from both helices are compared in Tpc Local Sector coordinate system at plane y = 123 cm.
  • Below plots for offset in coordinate and direction in bending plane are presented.

Offsets versus Drift distance  for West and East part of Tpc:

  • There is no offset dependence on drift distance => No space charge distortions
  • There is a clear difference (~100 mkm) for West part of TPC and no significant difference for East one.


The same plot with separation between Y2010 and Y2011 data. Again this plot confirm ~100 mkm offset for West part of Tpc for both runs.


After discussion with Maxim it was found that Run XI data were processed with ideal alignment. From this point it is interesting to compare misalignment for Run X (with alignment corrections) and Run XI (without those corrections). It is interesting that there is no big difference between "aligned" and "ideal" geometries.