[Clascomment] OPT-IN: Separated Structure Functions for Exclusive K+ Lambda and K+ Sigma 0 Electroproduction at 5.5 GeV with CLAS

[Volker Burkert]

The paper represents a significant amount of work, and is generally very well written. Here I have just a few comments:

General comment: The PDG2012 edition did something good and replaced the notations for resonances to not anymore 
use the partial wave contents (S, P, D,..)  but the N, Delta, Lambda, Sigma, etc.. followed by the spin and parity of the state. For example, the P13(1900) is now the N(1900)3/2^+.  I think we should use those notations consistently.  
 
page 2, para 1: Reference is made to gluonic excitations and a fairly old paper by Barnes and Close. I suggest to add a reference 
to the most recent LQCD paper  by J. J. Dudek and R. Edwards,  Phys. Rev. D85 (2012) 054016 where they explicitly include hybrid
 baryons in their LQCD predictions. 

para4: line 1: Bonn-Gatchina and Giessen models are NOT "DYNAMICAL coupled channel models", Juelich and EBAC models are. 
 I suggest to drop the "dynamical" in the sentence; all of them are "coupled-channel models".   

page 3, para 1, line 3: drop "Bonn",  .. it is the same as "ELSA".  

last two lines: While the PDG2012 list only those resonances with known couplings to KY, you may want to refer to the note in 
PDG2012 by E. Klempt and R. Workman  (https://pdg.web.cern.ch/pdg/2012/reviews/rpp2012-rev-n-delta-resonances.pdf ) 
which includes the results of the BnGa analysis that shows many more states with couplings to K-Lambda and K-Sigma. The 
fact that this note is included in the 2012 PDG edition is significant.    

page 4: para 2: " ..PDG lists a two-star P13(1900)..". This state has been upgraded to 3-star in PDG2012 based on the BnGa 
analysis of mostly the CLAS hyperon data.  

para 4, 2nd sentence is not very instructive. The main reason why different analyses give different results for the 
resonance couplings is that the non-resonance contributions are very poorly constraint because in an effective Lagrangian
 approach most couplings are unknown or only poorly know. This is different from pion production where the non-resonant 
couplings and the form factors are much better known, which leaves mostly the resonance couplings as fit parameters.  

page 5, para 2, 3rd bullet has same content as 1st bullet => merge them

page 7, para 1: replace resonance notations with PDG2012 notations. 

page 12, last para: Use of a 5cm lH2 target and a luminosity of 10^34 implies a 8nA beam current not 5nA. 

page 13: para 1: 3.64x10^5 K^+Lambda  events should be 3.64x10^5  e'K^+Lambda (without requiring the scattered electron there would be a lot more KLambda events). 

page 14, para 3: " 1.5% momentum resolution". On page 12, the momentum resolution was given as 0.5 to 1%. Which one is it? 

Page 18, Fig. 7: It is unclear to me what the message of this figure should be.  If we want to show how the various contributions vary with kinematics it might be better to represent the spread of the points in the angle bins and the W dependence with some shaded band. 

page 21, Fig. 9: The acceptances shown are perfectly symmetric in phi about phi=0 in all bins. Was an ideal detector assumed, and simulations done only over half of the phi range? If so, how were fiducial cuts included and field imperfections?  I am also quite nervous about using only 8 phi bins. In other analysis (npi+, DVCS) we found it necessary to go to up to 72 bins for the acceptance calculations to see the fine structure, before the data were later consolidated in fewer (18-24) phi bins. The results do dependent on the number of originally used #bins. What was the justification for 8 phi bins only, and was the effect studied?  

page 38: bullet 3. The data in ref. [16] covers a Q2 range of 1GeV and below, and the Maxwell model was probably fit to that part only, i.e. a large extrapolation in Q^2 ( and for some of the data also in W) is needed to compare to the present data.  That should be mentioned to put the discrepancy in some perspective. (Question: Has Maxwell seen the data?)  

page 44: Fig 21: The discrepancy at W~2.45GeV in many of the panels should be mentioned in the text. Do we have an explanation for this  strongly correlated fit result. Is there a reason why we should drop this particular kinematic point? 

page 46, Fig. 23, 24: These are interesting results that should be shown on a bigger scale. For example one could show just one Q2 value for each of the Lambda and Sigma channel, e.g.1.8GeV^2, and cut off the W range at 2.3 GeV as there is nothing interesting at larger W and the noise near W=1.4-1.5 GeV is only distracting from the interesting parts. Then blow up the vertical scale to make the bumps look more impressive. So, instead of showing 18 panels, I suggest to show only 6 and make them look more prominent. In the larger panels one could point to the s, p, d wave enhancements. 


That's it. 

Volker