[Clascomment] OPT-IN:Measurement of Exclusive pi0 Electroproduction Structure Functions and their Relationship to Transversity GPDs

[Luciano Pappalardo]

Dear Authors, 

thanks for this interesting paper and precise results. 
The paper is well structured, however the text still needs to be refined, 
especially in the introduction part. 

Below my suggestions.

Best regards, 
Luciano Pappalardo


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Abstract:
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line 3: "range Q2" -> "Q2 range"

line 8: "into A substantially better"

line 10: I would rephrase as: "The results, based on a large amount of 
         data confirms that"

line 11: "uniquely offers direct experimental access"
          -> "offers a unique experimental access"

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Line 5: "A goal of" -> "An important goal of"

line 7: "in terms of quark and gluon fields" (skip "their")

line 7-8: "Deep inlastic experiments" 
          -> "Inclusive deep inelastic scattering experiments"

line 16-17: "extract THE NUCLEON quark and gluon structure"  

line 41: "There are eight GPDs AT LEADING TWIST"

line 46: avoid begin a sentence with a symbol: 
         ". x is the average" -> ", where x is the average"

line 54-55: why defining k and k' if they have not been introduced 
            elsewhere? If you want to use them then define q as 
            Q2=-q2=(k-k')^2 in line 53. 

line 55: again, avoid beginning a sentence with a symbol:
         ". t is the" -> ". The variable t represents the"

line 59-60: "are reduced to" -> "reduce to"

line 61: "helicity distributions Dq(x)."
          -> "helicity distributions Dq(x), respectively, while
          H^q_T reduces to the transversity function h_1(x).
          (For completeness and to help the logic flow, it is better to 
          anticipate here this last part (transversity) rather than in 
          lines 70-71).
         
line 64: "THE Pauli form factor ..., THE axial-vector form factor..., 
          and THE pseudoscalar..."

line 67: "Most OF THE reactions studied"

lines 69-71: "Very little is known about the chiral-odd GPDs. They are 
              difficult to access since ...."
             (the part in the middle being anticipated at line 61 (see 
              comment above))

line 74: "description of THE nucleon structure"

line 76: "electroproduction REACTIONS"

line 77: there is maybe a blank space after the reaction, before the comma

line 77: "especially" -> "particularly"

line 89: "more difficult to measure than pi+"
         -> "more difficult than for pi+"


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line 1: "skip "than for pi+" (already clear form the previous line)

line 2: "the clean detection of pi0 requires the measurements of their two
         decay photons"
        -> "the identification of pi0 requires the detection of their two 
            decay photons"

line 3-4 "This letter ... GPDs" This sentence is out of context here.

FIG1. The figure appears too crowded and the meaning of the arrows 
      is not clear (not even explained in the caption). Eliminate the arrows 
      from te figure. They are not needed and everithing is anyway clearly 
      explained in the text (lines 8-15).
      Caption line 4: "THOSE OF the incident photon"
      Caption line 5: "and THOSE OF the active"

line 6: "linear sum of amplitudes:" -> "convolution of two objects:"

line 8: "1. The amplitude of a process in which ...."

line 16: "2. The GPD" (what is "F"??)

line 21-22: "the following: the GPD H_T, that characterizes..." 

line 24: "...+E_T), THAT characterizes..."

line 27: "in the unpolarized nucleon" -> "in AN unpolarized nucleon" 

line 29: there is maybe a blank space before "[9]"

line 29-31: "Thus E_T... we would like tro access" 
            What all this means? Try to rephrase and explain more clearly.

line 80: "by means of the following. The angle...."
         "by requiring the following conditions: the angle ..."

line 88-89: "using sidebands" -> "using the sidebands method"

line 95: skip "self" 
  


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line 15-16: rephrase as: "A systematic uncertainty of +/- 6% was applied
                          for this correction."

line 23: "estimated at about 10%" -> "estimated to be of the order of 10%"

Eq.1 Add full stop at the end of the formula

lines 30-32: I would rephrase the whole sentence as:
             "The interference terms sigma_LT and sigma_TT were extracted 
             respectively as cos(phi) and cos(2phi) moments in a fit of the                         differential cross section, together with the unseparated 
             sigma_U=(sigma_T+sigma_L) term."

line 37: add comma after "calculations"

line 42: "common kinematics" -> "common kinematic range"

line 44:  "in the limited region of overlap"
          -> "within the experimental uncertainties"
          (it is clear that the comparison is done in an overlapping region)

line 64-65: "GPDs H AND E"

line 85: "rather well WITH the data"

line 88: "dominent" -> "dominant". Do the ortography check to avoid typos.

line 94: attach the full dot to sigma_TT

line 106-107: skip "pseudoscalar"

line 108: "which is directly related to" -> "to probe"




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Caption of FIG2: "vs t" -> "vs -t"

line 3: "way BY looking"

line 4: "at THE unseparated"

line 12: "and THE longitudnal"