Hi Chris,
I agree with you that there are no obvious internal offsets anymore
and that one should move/rotate all three chambers in a sector rigidly as
a whole to see if the remaining shifts in phi and z go away. Remember,
also the-the(thp) is off by ~0.2 degrees (the sign of this offset is
reversed compared to the old crunch).
I think most promising could be a shift in Blast-x direction (that's how
the frame/subframes move in and out), and rotations in the xz and xy
planes.
Regards,
Michael
On Thu, 16 Mar 2006, Christopher Crawford wrote:
> I redid the analysis of the offsets of the middle drift chamber in each
> sector based on matching the momentum and angle for elastic events. (see
> http://blast.lns.mit.edu/PRIVATE_RESULTS/USEFUL/ANALYSIS_MEETINGS/meeting_050830/wc_ffr.ppt
> )
>
> Explanation:
> All three figures are plots of the same WC offsets, as a function of
> different variables: theta,phi,z
> In each plot, the y-axis is the fitted shift of the middle WC in cm (3x
> Doug's value).
> The top row in each figure is the offsets calculated from electron tracks,
> and bottom row protons; each for the left and right sectors.
>
> Observations:
> Obviously, the 1.2 mm shift in the right sector is gone. We are left with
> a strong dip (1.5 mm) at very forward angles, and then increasing gradually
> from -.5 to +.5 mm as a function of theta. But this is fairly uniform
> between the two sectors, and there is not such strong agreement between from
> electrons and protons as before. I see a little of the structure matched by
> the electrons and protons in the right sector on the order of 0.2 mm but one
> would need to match x_wc(theta_e) and x_wc(theta_p) to be sure it was due to
> geometry.
> Also, the dip around phi=0 in the right sector (electrons) has disappeared
> due to corrections to the magnetic field. The sharp 2 mm drop-off at phi<-10
> deg in the left sector has also softened (new field map?), and there is only
> a slight roll-off at the edges.
> The z-dependence also looks good, with the exception of z~-20, which may be
> an artifact or poor reconstruction at small theta.
>
> Conclusion:
> The inter-WC geometry is most likely OK now. Since there is fairly good
> agreement between the two sectors, the residual offsets we now see could be
> due to other factors such as radiation, or overall position/rotation of the
> wire chambers in each sector as a whole. I will try an exercise to fit for
> these parameters in the future.
>
> --Chris
>
+-------------------------------------+--------------------------+
| Office: | Home: |
|-------------------------------------|--------------------------|
| Dr. Michael Kohl | Michael Kohl |
| Laboratory for Nuclear Science | 5 Ibbetson Street |
| MIT-Bates Linear Accelerator Center | Somerville, MA 02143 |
| Middleton, MA 01949 | U.S.A. |
| U.S.A. | |
| - - - - - - - - - - - - | - - - - - - - - -|
| Email: kohlm@mit.edu | K.Michael.Kohl@gmx.de |
| Work: +1-617-253-9207 | Home: +1-617-629-3147 |
| Fax: +1-617-253-9599 | Mobile: +1-978-580-4190 |
| http://blast.lns.mit.edu | |
+-------------------------------------+--------------------------+
This archive was generated by hypermail 2.1.2 : Mon Feb 24 2014 - 14:07:33 EST