theta = 0 is used in reconstruction, everywhere.
When even the default theta in Wire.Cal is used, we get much worse
resolution. This was first discovered by Tong I think, because when I
first read his implementation of Doug's cubic t2d in library, he
explicitly passed "0" theta angle to t2d functions.
I tried to remove this behavior with cubic and later with 6-order
Garfield. but both time get considerably worse resolution. Therefore I
also decided to keep it just 0.
Chi
On Thu, 15 Jul 2004, Douglas Hasell wrote:
> Hi,
>
> After Chris' s presentation yesterday I looked at how nsed at least
> calculates the track position and it assumes the the track crosses the
> cell at 0 degrees ie perpendicular to the chamber. I don't know where
> to look to say whether or not the reconstruction does this properly or
> not. The so called default angle which is in the wire calibration file
> varies from -53 degree for cells at 20 degrees to 8 degrees for the
> cells at 80 degrees. So nsed at least does not use the default angle
> but rather fixes the track angle to be 0.
>
> Now it has been stated that using the track angle results in worse
> fits. My question here is then at what point is the proper track angle
> used? If the stubs forming the track are selected based on the results
> using 0 degrees and then the same stubs are recalculated using the
> track angle this may indeed result in poorer resolution. The proper
> procedure is to use the default angle as in the wire calibration file,
> determine the stubs from those positions which could result in
> different combinations of hits being chosen, and then refine it with
> the proper track angle once the track is found. Then the change should
> not be so great and possibly improves things. Going from 0 degrees to
> the actual track angle is a big change (eg a change of -50 degrees in
> the forward direction).
>
> The time to distance curve Chris showed yesterday showed the results
> of his improved fit and compared it with the "GARFIELD" result.
> Chris's result rose quickly from zero and then went linear about 2 mm
> above the GARFIELD result which rose less steeply from zero and then
> went linear. This is the behaviour using 0 degree track angle in a
> magnetic field. With higher track angles the rise is steeper. I
> suspect that if the GARFIELD result had been given the correct track
> angle the discrepancy with Chris;s result would not be as great.
>
> Chris: If you tell me which chamber, cell, layer, etc. you used in
> that plot I will calculate the correct "default" time to position
> curve.
>
>
> Cheers,
>
> Douglas
>
> 26-415 M.I.T.
> Tel: +1 (617) 258-7199
> 77 Massachusetts Avenue Fax: +1 (617)
> 258-5440
> Cambridge, MA 02139, USA E-mail:
> hasell@mit.edu
>
>
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:31 EST