[G8b_run] Response to comments

[Michael Dugger]

Hi,

I thank Ken and Franz for their thoughtful comments and suggestions. If 
I have neglected comments from other people in the g8b group, please let 
me know.

There were a few comments that I did not fully understand and will need 
clarification on. I have included my response to the comments at the 
bottom of this email.

I have a revised version of the analysis note at
http://www.jlab.org/Hall-B/secure/g8b/ASU/g8bPionAnaV5.pdf

--------------------
Response to Franz

Anyway, as mentioned last week, for an analysis note it would not be 
sufficient to put some 'typical' distributions out but also point to the 
ones with low statistics - in particular at higher energies; and to have a 
few plots on pi+n as well.

######
Response:
I have put a reference to a web location that contains all of the fits for 
both reactions.
######

Here are a few more things:

p.1, col.2: You are talking about extracting the beam asymmetry from FROST 
- but in reality it's the opposite: without a clean measurement on liq.H 
any FROST measurement is flooded by systematics. E.g. to K+Lambda I 
proposed to Ken to do the opposite: take Sigma from g8b as constraint to 
extract G (and for pi0, where we have some issues with background 
subtraction, it will be not different: so g8b results ARE crucial for the 
pol. target expts.).

######
Response:
We state "This analysis will provide $\Sigma$ for FROST.
It will be helpful for FROST to have stand alone measurements of $\Sigma$
to separate the effects of beam asymmetry from the effects of beam-target 
asymmetries."
######

p.2, col.1: g8b target was not really at center of CLAS but at -20cm (i.e. 
downstream end at CLAS center)

######
Response:
Fixed
######

p.2, col.2, Section III: first paragraph: you talk about 'good momentum 
and scattering angle info.' and then 'very good velocity and momentum 
determination'.

######
Response:
Changed to "Time-of-flight information, coupled with the track information 
provided by the drift chambers, determined the velocity."
######

next paragraph: the 'theoretical value of beta' uses momentum from CLAS, 
but the measured value uses timing information and track length!

######
Response:
I don't see a problem with the statement in the analysis note. Can you 
elaborate.
######

p.2., col.2 Section IV: This selection cut out files and runs that clearly 
had serious problems (skip: 'therefore likely unsolvable' because we still 
can improve timing and other issues ... given more time and efforts)

######
Response:
Changed to
"This selection cut out files and runs that clearly had serious problems."
######

p.5, col.1: what was the reason to only take protons > 0.9 GeV (best 
resolution starts ~0.6 GeV) ... only saying you cut out a lot of good 
tracks.

######
Response:
I needed to make such a strong cut on momentum to get good convergence.
######

p.15, col.2, section VIII: item 2. you meant 'where X=pi+pi-' isn't it? 
Same p.16, col.1: "the {\emshape} of the pi+pi- component ..."

######
Response:
Fixed.
######

p.16, Fig.24 caption: Note 'right panels' but 'bottom panels'

######
Response:
Fixed.
######

Please keep all your information on photon energy correction and moment 
analysis in this note (CLAS-notes are only pieces of paper with a number 
on the top right of the first page).

######
Response:
Agreed.
######

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

Response to Ken

General Comments.
Everything is here is detail, which as a g8 person I found very 
interesting. For the reviewer I'd be inclined to remove some of the detail 
which is already covered in CLAS notes and give summaries, and include 
CLAS notes as supporting documentation.

######
Response:
We have decided to leave in the long discussions.
######

I Intro
It should say somewhere that the beam was polarized using the coherent 
brem technique and that g8 was the 1st experiment at Jlab to use this.

######
Response:
I put:
"The g8 run period was the first Jefferson Lab experiment to use the 
coherent bremsstahlung technique to produce polarized photons." in section 
II.
######

IV Valid Run Subset ...
I'd cut this down to a summary paragraph explaining that it's on the basis 
of no of protons per sector, but takes into account the coherent edge, and 
whether the runs contain PARA, PERP or AMO data. with a couple of example 
plots and reference to the CLAS

######
Response:
We decided to leave in the long discussion.
######

V Correction ....
Should this not be Momentum and Photon Energy Correction?
It's seems to be implicit that momentum corrections were also applied.
Again, I suggest leaving most of this as reference to the CLAS note. I 
suggest keeping Fig12 and Fig 14.

######
Response:
Changed title to include momentum corrections.
We decided to leave in the long discussion.
######

VII Fourier moment ..
This is a very nice discussion, but again I suggest a summary and 
reference to the CLAS note. Ending on the comparison of moment and phi bin 
methods.

######
Response:
We decided to leave in the long discussion.
######

IX I'd summarize and refer to the CLAS note.

######
Response:
We decided to leave in the long discussion.
######


Specific Comments
p1, col1
I suggest replacing the extraction of the  observable the extraction of 
the photon beam asymmetry observable

######
Response:
Changed wording as requested.
######

P1, col 1 (and elsewhere)
I suggest saying parallel to the horizontal plane of the detector's 
reference frame, rather than parallel to the floor

######
Response:
This is an issue of style. Saying parallel to the horizontal plane of the 
detector's reference frame is the same as saying parallel to the floor
######

P1 col 2. Top should be top.

######
Response:
Fixed
######

P1 col 2. Should it not be disentangling instead of unentangling.

######
Response:
The word "unentangling" was not used in the document. I assume that
you meant to write "untangling". Decided to change "...valuable for 
untangling..." to "...valuable to disentangle..."
######

Fig16 top is Mass^2, bottom is Mass.

######
Response:
You are correct, but there is nothing wrong with this. The top panel is 
the missing mass squared for the "gamma p -> p X" reaction and needs to be 
in mass^2 since the pi0 mass is close to zero. The bottom panel is the 
missing mass for the "gamma p -> pi+ n" reaction and since the neutron is 
so far from zero, there is no need to use mass^2
######

P16 You don't say whether you anything about the background in getting 
sigma. Do you assume negligible, or assume unpolarized and account for 
dilution, or measure background sigma and take account of it?

######
Response:
I am confused about this comment. There is a discussion regarding the 
background subtraction on page 16. I feel like I am missing something. Can 
you restate your comment?
######

IX Need a summary of the polarization tables and a reference to the CLAS 
note (going in in a couple of days).
In the intro, it should define the coherent peak and coherent edge (also 
in the fig caption) and say that there is a high degree (up to 90%) of 
polarization under the coherent peak. Here's a rough attempt at a summary 
to go at the end of the intro paragraph in IX:
In the ideal situation, for any chosen coherent edge setting the coherent 
peak would be stable and a single lookup table would be used to relate the 
degree of polarization to the photon energy. However, in practice, the 
coherent peak drifts around in time  reflecting variations in beam 
position and angle, and position dependent variations in the crystal. An 
example of the variation is shown in Fig 28. The drift of the peak 
position is handled by having a collection of tables corresponding to the 
spread in the coherent edge position for each setting. The coherent edge 
is determined from the tagger E-counter scalers which are read into the 
data stream at 2s intervals, and the appropriate lookup table is selected
on the basis of the current coherent edge position. The process of fitting 
the coherent bremsstrahlung spectra is described in a separate CLAS note 
[ref KL to be submitted].


######
Response:
I have included the suggested text.
######

Fig 28. I have a better version to replace this with. 
(http://nuclear.gla.ac.uk/~kl/g8b/allperp.gif )

######
Response:
I replaced plot with requested version.
######

P21(C.)
Statement about the 2.1GeV data needs to be fixed. We need to decide what 
to do about that.

######
Response:
I changed the text, slightly, to read:
"The 2.1 GeV data set should not be modified using the procedure described 
in this document. To correct the polarizations within the 2.1 GeV data a 
different technique must be used."

I do not what else can be said about this. Let me know if you have a 
suggestion.
######

-Michael