[Clascomment] OPT-IN:First measurement of the helicity asymmetry E in eta photoproduction on the proton

[Reinhard Schumacher]

Hello ASU Folks,

Your draft CLAS paper on the E asymmetry for eta photoproduction is
well written.  The goal of the measurements are clearly stated, the
experimental analysis is well presented, and the experimental results
are easy to absorb.  I think you need to work on the interpretation
and discussion sections.

My concern is about how you place the results in the wider context of
the state of theory.  Foremost, the paper lacks focus concerning the
existence, or lack thereof, of a narrow state near 1685 MeV.  If you
read your reference 7 from the Bonn Gatchina group, they do NOT claim,
as you imply on lines 20-22, that there must be a narrow structure.
They make a big point that the structure is compatible with the
interference of two resonances within the S11 partial wave.  The
"exotic" interpretation is not excluded, according to them, but it is
wrong to say, as you do, that "this particular state is believed to
have been observed in eta photoproduction" and cite them as a source.
I think you have to soften this statement to say "a state at this mass
is one of several explanations for observations in various reactions
of structure at this energy".

Paragraph starting line 132: It is always better to start with a
picture.  I think you should introduce Fig 1 first, and only then
proceed to discuss how you handled background.  My first reading left
me confused, since you had not yet shown the reader what the data look
like.  I wanted to ask you what was the nature of the background and
how you modeled it, but then when you finally got to introducing
Fig. 1 it all became clear.  Thus, I would restructure this paragraph
to introduce the figure first.

line 174:  Why is the beam helicity ratio unknown at the level of 2.1%?
That is big!  In other run periods the ratio was known to a small
fraction of a percent. 

Line 207: Here you refer to "a Juelich fit", as though everyone knows
what that is.  The paper is ineffective in explaining the impact these
data have on models, including this Juelich model.  I think you could
do better here by devoting several sentences to introduce what the
Juelich model IS in this case.  What did they have to change to fit
your data?  Did they just tweak a few parameters, or did they have to
undergo some paradigm shift?  Without this information the paper is
weak.  If you need to save some space, you can remove the present long
sentence starting at line 225, where you congratulate yourselves
"dramatically" for your new results.  It would be more effective to be
modest in tone and explain specifically what changed in the model
calculation.

Another way to say this is as follows.  At the beginning of the paper
you raise the issue of the nature of the structure at 1685 MeV.
Indeed, this is an interesting question.  At the end of the paper you
completely fluff the conclusion: i.e. you have nothing to say about
this issue any more.  This leaves the reader with a deeply unsatisfied
response.

Ref 23: fix umlauts.

That's all for now.  I think this can be make into a substantially
better paper with a little rewriting!


Cheers,
Reinhard