[G8b_run] Tagger Sag

[Barry Ritchie]

Volker, though I'd heard about the sag long ago, I was unaware of this
paper. 

At any rate, since "the saga of the sag" continues as the deformation
seems to continue to grow, every run group should do what we've been
doing. I think this is contrary to the conclusion reached in the paper,
though:

"The analysis presented in Ref. [3] was repeated with the new
calibration constants and showed similar improvements in the energy
determination. The data in Ref. [3] were from a 1999 CLAS run, while the
data used in this analysis and the data presented in Fig. 12 were taken
in 2004. Comparison of these two sets of data shows that the geometry of
the tagger focal plane did not change during this five year period and
that the sagging and misalignments were introduced at the time of the
tagger construction."

Brian Vernarksky's analysis would also suggest the sag is changing, if I
understand him correctly. 

BTW: Notice that the variations observed in Figure 12 are on the order
of +/- 2 MeV or so.

---BGR



Professor Barry G. Ritchie
Department of Physics
Arizona State University
Tempe, AZ  85287-1504
 
Telephone: (480) 965-4707
Fax: (480) 965-7954

-----Original Message-----
From: g8b_run-bounces at jlab.org [mailto:g8b_run-bounces at jlab.org] On
Behalf Of Volker Crede
Sent: Friday, October 23, 2009 1:29 PM
To: g8b
Cc: Volker Crede
Subject: [G8b_run] Tagger Sag

Hi all,

Mukesh Saini in our group has just pointed out that there has been a
2007 
NIM paper on the "Energy calibration of the JLab bremsstrahlung tagging 
system" by some CLAS members (S. Stepanyan et al.): NIM A 572 (2007)
654.
I tried to attach it to the email, but the file is too  big. They
describe 
a tagger photon-energy correction for CLAS which is needed to account
for 
a possible sag of the frames holding the E-counters. They say there was 
"corroborating evidence from simulations of the effects of gravitational

sagging and various possible misalignments of the tagger focal plane". 
Figures 11 and 12 look very similar to our tagger sag plots.

Mukesh has been working on the tagger calibration for g12 and pointed
out 
(he believes) that the correction is in the tagger package for g12 and 
possibly for all runs after 2007. According to Mukesh, we can simply
look 
into the tagger code and find out what the correction is.

I will have a closer look at the paper over the weekend. Is anybody else

aware of this publication? I hope it's not just us ...

Best wishes and have a good weekend

    Volker

----------------------------------

Volker Crede
Assistant Professor
Florida State University
Department of Physics
206 Keen Building
Tallahassee, FL  32306  USA

Phone: 001 850 644-2423
Fax: 001 850 644-4478
crede at fsu.edu
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