[Clascomment] OPT-IN: phi-meson photoproduction on Hydrogen in the neutral decay mode

[Volker Burkert]

Dear Heghine and Moscov,

This is an important paper. We like to make it as good as possible. Here are a few comments that 
you should consider.

Introduction: 
 Left column: line 6: The statement is too strong. There are model analyses by J.J. Xie, B.S. Zou, H.C. Chiang, 
Phys.Rev.C77 (2008) 015206 that discuss evidence for N*(1535) ->N-phi coupling, and a bit more general 
in terms of qqqs-sbar contributions in:  C. S. An, B. S. Zou, Eur.Phys.J. A39 (2009) 195. These papers should 
be referenced. 
You may also say a few words with references to the CLAS phi-electroproduction publications, and in case 
the charged channel phi paper makes it to the arXiv's in time, reference it as well. 
 
Background selection.
As a signal function for the background evaluation a Breit-Wigner form is used with the width of the 
phi (=4.3MeV). However, the actual signal “width” appears to be more like 15-17MeV in Fig. 5, which means 
that the width is dominated by resolution effects. Therefore the fit should include a function convoluted 
of a Gaussian and a Breit-Wigner form, also known as a Voigt profile (http://en.wikipedia.org/wiki/Voigt_profile). 
Further down it says: “The fit at the very backward angle has very large chi^2 due to the limited statistics 
at large angles”.  I assume you mean the reduced chi^2. The statement makes no sense as the reduced 
chi^2 = chi^2/#DF, should be independent of statistics. In any case you should  give the chi^2/#DF values. 

Systematic uncertainties. 
The acceptance cut is either not well described, or not justified. If I understand it correctly, it may bias 
your data. Please describe the procedure in more detail and explain why it does not bias the results. 

Figures. 
Fig. 7 and Fig. 8. The high density of the data combined with the large symbol size makes the graphs difficult 
to read. You may want to reduce the symbol size.  Also, the systematic error histograms dominate the appearance 
of the graphs. You may use a light grayish pattern or just unfilled white histograms. 
Fig. 9, 10.  I have the same comment on the systematic error histograms. Use a light grayish pattern or 
just unfilled white histograms.   
Fig. 11, 12. 
The data points at large energies and backward angles are impossible to distinguish from the zero line. 
In order to make the data useful for the reader I suggest to tabulate the cross sections for all bins. There 
are about 20 energy bins and 14 angle bins, i.e. 280 data points that could easily be accommodated in a 
few extra pages.  There one should also include the statistical and systematic errors.  
Fig. 13. 
I suggest you use different symbols for the CLAS data, e.g. red-filled black circles that are slightly larger 
than the other symbols, the latter should be shown as open symbols. The CLAS data should dominate 
the appearance as they represent a more complete set covering the entire bump structure as well as 
the transition to high energy. 

Volker