[Clascomment] OPT-IN: First Observation of the Line Shape of the Lambda(1405) in Electroproduction

[Volker Burkert]

Dear lead authors,
This is an interesting paper with potentially far reaching conclusions. We want to be sure 
that the conclusions are supported by the data and the analysis. Dan Carman made already 
many comments in this directions, many of which I agree with. I just wanted to add one 
more concern related to Figure 8. The conclusion from the figure adds really new 
information beyond what the previous paper on the Lambda(1405) line  shape already 
found, i.e. the complex structure of this resonance. The main message of this paper 
is that the higher mass structure of the two structures behave differently with Q2 than 
the lower mass structure and appears to show a harder form factor behavior, similar 
to the Lambda(1520). There could be interesting consequences in terms of underlying 
resonance structures if this is indeed the case.  Unfortunately, the current analysis 
leaves some questions to be addressed that I briefly discuss here:  

Resonances are characterized by fixed masses and fixed widths. These are independent 
of Q2. However, the fit to the data at different Q2 ranges uses Breit-Wigner masses and 
widths, which apparently were left open to be fit in each Q2 range, separately. This leads 
to a changing first BW peak position from 1350MeV (at low average Q2) to 1365MeV (at high 
average Q2) as well as a changing width, and for the 2nd peak position a change from 
1400 MeV (at low average Q2) to1420 MeV (at high average Q2) and a width changing 
from ~60MeV at the lowest average Q2 to  ~20MeV at the highest average Q2. 
This variation in fit parameters shows that some contribution is missing in the fit. 
In order to come to conclusions that are more supported by the data the fits should be 
done with fixed masses and widths for the Breit-Wigner forms and these parameters 
must be independent of Q2. Only then can the two BW amplitudes be compared and 
more definite conclusions drawn regarding the Q2 dependence. 

Volker