cms-sw/cmssw — pull request #2722 by cbaus (2014-03-05 01:14:58+00:00)
Title: Updated CASTOR geometry to support to separated halves

Why we need the change:
The updated geometry can decribe a gap in the 2 (physical) detector halves. Previously castor was only 1 geant volume. We have reason to believe that due to the magnetic field castor is separated by ~1.5mm. This commit keeps the nominal position in castor.xml for the moment.

What is changed:
This includes changes in the sector to volume numbering scheme in order match the original numbering (CastorNumberingScheme.xx)
The geant volumes are duplicated and each half contains 8 sectors. (castor.xml)
Also added the possibility for a rotation or tilt as we call it. (castor.xml)

Validation:
The geometry has been validated extensively in CMSSW_4_4 (we will prepare some slides) and I just ran for 7_1_X 500k pion events (each old and new) and compared nominal to nominal which looked good in the statistical uncertainty.

Future:
We already obtained a position from different measurements in 2013. This has to be integrated.
One remark. The position can in principle change for each run. It may be needed to store x and y for each half in the database. I will discuss this in the next CASTOR meeting. The changes here will still be required.

Example for validation plot:
![Comparison for sector numbering](https://f.cloud.github.com/assets/5031063/2328646/6df56e38-a403-11e3-879b-d4ca8b77b0b5.png)