[Brahms-dev-l] comments to analysis (geometry)

Hi Ian
Thanks for the initiative to summarize the task to be done.
I will like here to comment on a few specifics, that shows these first taks will only be preliminary, and will have to be redone later and better.

-geometry
As always this is not an easy issue. Let me restate what I know
-T5 has been taken in/out. It was resurveyed at least once; for the first value the survey group was not happy- it was repeated but I have not seen the numbers.
T4,T4 was repositioned or rather levelled since there was known to be a significant rotation in the XY plane (Pawel Oct 03).
- T1 was moved significantly, and resurveyed. T2 is not knowned to have been moved. If you dare to look at 0-field runs you will see a significant difference in the T1-T2 matching even though the survey was put into the DB (6-8 mm!!!!!)
For each angle setting one CANNOT assume the t2-t3 alignement is good. As I understand matching files and the way they are applied, this is not sufficient for being able to use T2-t4 tracks for determining momentum even though this is what has been done.
So there are different issues here
- some do need re-survey after the run (MAY 04)
- other can be solved by doing DC geometry T3-T4-t5 w/o inclduing t1,t2 that I do not trust well at this time

Actions:
a) get Krakow group to optimize t3,t4,t5 geometry (after calibrations) (PS)
b) ensure survey is done after run.(fv/db)
c) look at prelim T1 modifications (geom)9/fv)
d) try to understand why (or why not) T1 tracks do point in Y to T2 and vertex after TPC has been calibrated.
   (did anyone ever look at absolute fibre positions not just differences ??) (who??)

/fv

----------------------------------------------------------------
Flemming Videbaek
Physics Department
Brookhaven National Laboratory

e-mail: videbaek@bnl.gov
phone: 631-344-4106



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