[Clascomment] OPT-IN:Differential Photoproduction Cross Sections for the Sigma0(1385), Lambda(1405), and Lambda(1520)

[Volker Burkert]

I am sending this again as my first attempt at sending it to the clascomment repository apparently
had failed. There is nothing new in here that you have not seen before, I am sending it just for the record.

Dear Kei and Reinhard, 
This is a very interesting paper and it is good to see how much information can be extracted 
from the high statistics of the G11 run. I don’t want to comment on the editorial aspects here 
but I came across one potential flaw in one of the results. As is commented in the paper the 
cross section for the K-Λ(1520) shows an unexpectedly sharp drop for the first bin in W 
compared to the next higher W bin. It also undershoots by a factor 2 the theory curve as 
well as the LEPS data, both of which are in good agreement with our data for the next higher 
bins in W. I have the suspicion that acceptance may not have been correctly taken into account 
for this first W bin. The bin width is 100MeV and extends from W=1950 to 2050 MeV.  

However, the nominal threshold for the process γ + p → K+ + Λ(1520) is at 
Wthr = 2013.2 MeV [= 493.7 + 1519.5  (peak)], or if I subtract  Γ/2 = 7.8 MeV [half of full width of Λ(1520)], 
it is still Wthr=2005.4 MeV.  This means that the production threshold is about 55MeV above 
the lower edge of the lowest W bin, and the bin is thus only about 45% filled 
(neglecting resolution effects).  If the acceptance for this bin was calculated the same way as 
for the other bins, i.e. acceptance = Monte Carlo events accumulated in bin/ nominal bin width, 
the cross section will be about 50% low.  

I also noted that this lowest W bin is not included in the total cross section graph in Fig. 11, 
where the bin center would have ended up just below threshold.This is, of course, a well-known 
problem with edge bins that go across the production threshold, and our very first paper 
(phi photoproduction) showed the very same problem for the last bin in t. Fortunately, 
it was detected and fixed before publication. 

These kind of problems should have been caught 
in the PWG review, and the fact that the cross section is 50% lower than the LEPS data show 
may have caught the attention of the ad hoc committee as well, and perhaps all this was 
scrutinized and discussed already, in which case I apologize for bringing it up again. 
However, the effect is so striking and seems highly unphysical, so I felt necessary to bring 
it up as a possible issue. 

There is another thing that look suspicious to me, the drop by a 
factor 4 of the K-Λ(1405) cross section for the lowest W bin in the Σ0π0 channel around 90deg. 
This drop occurs from one angle bin to the next. However, I don’t suggest an explanation for 
such a behavior, but it would be good to make a comment in the paper that this was scrutinized 
and found to be correct as far as the analysis is concerned. 

Volker