OPT-IN: Exclusive Ï0p electroproduction off protons in the resonance region at photon virtualities 0.4 GeV2 ⤠Q2 ⤠1 GeV2

[Volker Burkert]

Dear lead authors,
This is an important paper and it should be written better than it is now. I have some general remark first 
and more detailed remarks in the next mailing.
Volker

1) INTRODUCTION requires major rewriting. 
  a. It is laid out too broadly and discusses things that may be better reserved for a discussion at the end.  
  b. It refers to "CLAS" 13 times in  just two pages. There is no need for that and it makes the reading
     cumbersome and detracts from the main message. 
  c. It is too long. Half the length should be sufficient to discuss the reasons for the measurements and 
      what specifically it adds to the already accumulated volume of data.  
  d. It refers several times that the various Npi and p-pi+pi- electroproduction data "validate" previously 
     published CLAS data. To me that would imply that we are not sure what we published is actually
      correct.This is not only wrong but could be damaging to CLAS. When we publish data or analysis
      results our combined statistical, systematic, and model uncertainties should give us confidence that 
     the published results are correct within these uncertainties. Similr phrases are also used in the Results 
     section.  
    Qualifications such as "reliable" or  "credible" or "remarkably" or  "the successful description" or the
     "impressive success" and others are out-of-place here. 
 e. The phrase "for the first time" is used at least 3 times (line 82, 170, 182).     

2) RESULTS and DISCUSSION repeats some of the "validation" comments (e.g. line 633 - 643, 660)  
    Line 749 - 755 The phrase "The reasonable description .... suggests promising prospects..." 
    is not a convincing phase.   
    Line 715: Why not discuss results/interpretation from Legendre Polynomial fits in this section than 
    referring to the web page?.  The JLAB/YePhi models is mention several times as a "reaction model".
   I don't think this is correct. It is a unitary isobar model with parameterization of the resonance contribution
    and of the background, similar to MAID. The other model is based on fixed-t dispersion relations to
    compute the real non-resonant contribution from the resonant amplitudes and add pion pole term.    
    A resonance N(1685)5/2+ is mentioned at least twice. It does not exit in PDG. Probably you meant 
    N(1680)5/2+ also mentioned elsewhere.   

3) FIGURES:  
   The kinematics in Fig.1 is not a very good representation. Take a look at Fig.4 in your reference [2]. We could
   modify that easily for p-pi0.  
   The results shown in Fig.17, 21-25 should have bigger markers. The 3rd panel in Fig.24  has strange results at 
   large W, with a huge jump near 1.7 GeV, which looks unphysical. If that is not a mistake than there should 
   be comments in the text explaining the behavior. Also, how can the error at W=1.7 be so large for Q2=0.95 
   while the data points at neighboring W values have order magnitude smaller errors.