[Clascomment] OPT-IN: Transverse Polarization of Sigma+(1189) in Photoproduction on a Hydrogen Target

[Volker Burkert]

Previous comment was incomplete. 
Volker


Hi Chandra, 

 It is good to see that the CLAS data have sufficient statistical sensitivity to show 
real interesting behavior. I have a few comments about this and some suggestion.
Several readers have already commented on other aspects of the paper, with which
I agree,  and I will not repeat those here. 

However, I want to point out that in Table II and Table 
III on page 9 your energy bins, that you give as +/- 0.167 GeV are twice as large as they should
be. For example you show in the 1st bin E=1.25+/-0.167 and the 2nd bin E=1.42+/-0.167,
which means your 2nd bin reaches down to the center of the first bin rather than to the upper
limit of the 1st bin. All bins should be +/-0.0835GeV. Also, I am a bit puzzled with you using
different photon energies and bin sizes in table II an table III vs table IV. Similar comment 
on theta(Sigma). Why do you use theta in one place and cos(theta) in the other?  It would be 
better to have consistency. 


  
Here is my main physics comment:

The introduction refers to the "missing resonances" problem. I think this is exactly what 
you should be focussing on. Unfortunately, you neglect to reference some of the recent 
publications that claimed evidence for new baryon states particular using the new CLAS
data on hyperon production (K-Lambda, K-Sigma) and the polarization data for these 
channels. The publications you should be referring to are from the Bonn-Gatchina group:
 A.V. Anisovich, et al., Eur.Phys.J.A47 (2011) 153 and Eur.Phys.J.A48 (2012) 88. The latter 
shows a table with the coupling to KY final states of some newly claimed nucleon resonances
in the mass range of 1.9 - 2.1 GeV, several of which made it in the PDG 2012 including
states coupling to K-Sigma.   

Your discussion in section VIII. completely neglects a discussion of the nucleon resonance 
aspects and only discusses aspects that have nothing to do with resonance formation. The 
only comment where the resonance region is indirectly mentioned ins in the comment 
that there are "systematic differences of about 1 (in polarization) at sqrt(s)=2GeV".
Indeed this is very significant and the fact that the transverse polarization is qualitatively 
different where evidence for new resonances has been seen and published should be 
mentioned. I suggest to add one or two graphs showing the very different behavior of
the polarization in the "resonance" regime and the "DIS" regime. If you plot the polarization 
in Table IV, at the Eg=1.62GeV (sqrt(s)=1.97GeV) bin versus the cm polar angle of the Sigma^+ 
you will see a variation from P=-1.08 to P=+0.34 in the angle range covered. If you plot
the same at the bin Eg=3.12GeV (sqrt(s)=2.55GeV) you find the polarization to remain 
negative between -0.43 and -0.91.  
This different behavior is highly significant. It shows that there is NOT one mechanism that 
could explain the main observations, even not qualitatively. You discussion should 
emphasize this difference and conclude that your data may have significant impact
on the search for new nucleon resonances once it included in a coupled channel analysis.     

BTW, I would prefer the data be listed and plotted vs sqrt(s) as they cover mostly the resonance 
region, where resonance masses are identified as sqrt(s). Maybe you could add a row with sqrt(s) in 
table II and table III and a column with sqrt(s) in table IV. 

Volker