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

[Reinhard Schumacher]

Hello Ivan et al., 

I have read your paper "Measurement of Exclusive pi0 Electroproduction
... Transversity GPDs".  I think the CLAS measurements look nice, and
are worth publishing.  However, are you not overstating the
significance of these data in relation to the extraction of
transversity GPDs?  To be scientifically honest, you have to compare
your results not only to the currently-fashionable GPD approach, but
also to other approaches (of which there are several) that may explain
the data just as well.  To have a chance of getting accepted in a
top-ranked journal like PRL, you had better do this.

Here are my comments in sequential order:

page 1 line 14 the Regge references are not a unique, are they?  The
reader would like to read about the full range of previous work.

page 1 line 22: you make a sweeping introduction without giving the
reader a starting point to look into the literature.  Add a reference
here.

page 1 line 38: "...appear to be well described..."  this calls for a
suitable literature reference.

page 2 line 3: "This letter focuses..."  This sentence is a
non-sequitur from what came before.  Move this sentence to some better
place.

page 2 line 5 - 23: none of this discussion is about your own work,
and none of it seems to matter for what comes later in the paper.
This discussion does not help the reader appreciate your results.  To
first order, all this can be deleted, or greatly condensed.  In the
space created, you could discuss alternative models to the one
presented here as a way to explain the CLAS results.

page 2 line 80: I think you mean "...was selected as follows."

This paragraph of descriptive material could use a figure so the
reader gets some idea of the quality of the CLAS data.  I don't have
any specific suggestion, but it just seems to me that you have a
"hole" in the paper here.

page 3 line 12: why is the normalization factor 12%?  Is it the case
that your measurement is cross-normalized to other measurements?  Is
that what this sentence is supposed to say?  Or are you saying that
the final uncertainty in the normalization is 12% and you made an
absolute measurement?

page 3 line 92 to 96: various typos.

page 4 line 5: "The CLAS data..."  this seems to be a vacuous
sentence. You could just delete it and the paper will be better.

Awaiting the next draft of the paper...

Best Regards,
Reinhard