[Clascomment] OPT-IN:First Measurement of the Polarization Observable E in the p(gamma, pi+)n Reaction up to 2.25 GeV

[Volker Burkert]

Hi Steffen, 

I have a few comments on the letter. 

page 1:
line 16: replace "claim the existence of fewer states" with "have found a much smaller number of states"

line32:  after "single-spin observables "  add ", which do not form a complete set of observables." 

eq (2): Define E = 1/2 - 3/2 / (1/2 + 3/2), which I think is the standard definition (same for eq.(4) and (5). 

line 51-56: "The most striking ...." Here we are vetting the appetite of the referees to learn more 
about this new state, but they are referred to another follow-up paper. I think if we want to keep the
reference to the new state here we need to show at least some of the evidence later in the letter. One 
way could be to show from Fig. 2 in the follow-up paper (which is not a collaboration paper) the curve 
for Delta chi^2 of the pi+n reaction, showing the dip at the mass of the new state. Since the follow-up 
paper includes other channels as well, and the BnGa folks are already co-authors on this paper as 
limited CLAS members, we would not take away too much from the follow-up paper. 

line 61: replace ".. for the first time the full resonance region."  with ".. for the first time double-polarization 
data have been extended into the poorly explored mass range up to 2.3 GeV." (it is definitely not the 
full resonance region as there are 4* states known at much higher mass). 

page 2:
line 21: reference [14] points to the old start counter. I think since 2004 only the new start counter was used.
New reference Y.G. Sharabian et al., Nucl. Instrum. Meth. A556 (2005) 246. 

Fig. 1. I suggest to add another experimental figure before Fig. 1, for example the z-vertex reconstruction that 
shows the butanol and the carbon part. 

Fig. 2: To make the letter not too long, with the additional experimental graph, I suggest to show 
only 4 (bigger) panels in Fig. 2. The low mass panels are boring. I suggest to show only W=1.37 GeV as a reference 
that shows excellent agreement with model projections from previous analysis fits. It also shows that the data
follow precisely the trend towards E->+1 at 0deg. and 180deg. For the 3 remaining panels I suggest 1.8 GeV, 
where the shape is already quite different and more structures are seen, and 1.96 GeV, and 2.2 GeV where 
the discrepancies to the predictions become most visible. On a bigger scale one could also show the BnGa 
fit and see distinctive differences among the various models. 

If we follow the suggestions to include results from the BnGa fit and evidence for a new state, then the 
conclusions should also be changed and the reference to the follow-up paper can be that it will show many 
more details and convincing evidence that includes also other data sets. 


Cheers,
Volker