[Clascomment] OPT-IN: Measurement of the beam spin asymmetry of ep -> e'p'eta in the deep-inelastic regime with CLAS

[Volker Burkert]

Dear lead authors,
 This is a well written paper and I have only a few comments. Good luck with the PRL.
Volker


line 14 (abstract); it is better to replace "were" with "are". 

line 44-47: The spatial distribution of the quark spin is related to the second Mellin moment (also referred to as Ji sum rule)
 of the GPDs H and GPD E , not of H-tilde and E-tilde.( E-tilde has to do with induced pseudo-scalar form factor, and the 
pion pole.)   

Equation (1): Here the GPDs are called F. To avoid confusion for non-expert readers, you should state that the F's stand 
  for all previously introduced GPDs. 

line 115: " <F> and <F_T> represent the chiral-even and chiral-odd convolutions. Please explain how the "convolutions" 
            are defined. Are these just the products of GPDs or are these convolution integrals?  

line 130: The experimental measurements .... => The measurements... or   The experiments... 

line 136:  4.5 T => 4.5 Tesla 

line 180: "worst"  => "lowest" 

line 285-286:" .., where the latter can be ascribed to the onset of Bjorken scaling" => replace "the onset of" with "approximate". 
 ( "onset of" is more like "the beginning of"). 

line 291-292:  ".. thus allowing to separate real and imaginary parts of transversity GPDs."  
       Are "transversity GPDs" differently defined from the chiral odd GPDs? If not, then just use the chiral odd GPDs.      
      Also, I thought that GPDs are real numbers, with  no imaginary part. However they appear in observables, such 
      as the Compton Form Factors in complex form through convolution integrals.  
      Please make sure that when using the term GPDs, they are clearly defined and not confused with convolutions 
      of GPDs.

line 295:  " .. largely underestimated" maybe use "significantly underestimated". 

line 298:  Goldsten => Goldstein

line 318:  "Neither model appears to account.." => "Neither model accounts .." 

line 372: " , will provide new constraints to existing GPD models and will play an important role in the future GPDs quark flavor.."
             =>,  provide new constraints to existing GPD models and play an important role in the GPDs quark flavor.."