[Clascomment] OPT-IN: Photoproduction of the f1(1285) Meson

[Igor Strakovsky]

Dear All,

Moskov has a problem to put his comments and asked me to inform you folks about
his concern. 

Here you are...

Amaryan, Moskov
3:55 PM (0 minutes ago)

to Igor 
Begin forwarded message:

Dear Reinhard et al.,

I carefully read a paper draft and have some serious concerns which I describe below.

The signal of f1->\pi^+\pi^-\eta has been estimated from the distribution of the missing mass of the proton with a cut on the missing mass of p\pi^+\pi^- to be in the region of the \eta mass.

This alone can not eliminate a background coming from other decay mode like f1 or etaprime decaying to \pi^0\pi^0\eta(\pi^+\pi^-\pi^0). The missing mass of p\pi^+\pi^- still can be in the mass range of \eta, however those events will not be in the peak of \eta, but rather in the background under that peak. The analysis of reaction \gamma+p->  p\pi^+\pi^-\eta was performed in LMD group, based on g12 data set by Cathrina Sowa and presented in HSWG meeting during CLAS Collaboration meeting. 

The point I am drawing your attention is clearly demonstrated on page 9 and 10 of her talk, where as one can see there is significant contribution into etaprime peak from 
1-Q weighted events and almost comparable peak of f1 from the background events.
This will affect number of signal events and therefore extracted cross sections and branching ratios will be corrupted. In particular this may explain why the ratio of \Gamma(\gamma\rho^0)/\Gamma(\eta\pi\pi) is by factor of two less due to enhanced signal because of background events. I am convinced that the correct procedure should use  
\eta particle Q weighted events for the parent particle f1 or etaprime. 

This raises also another concern on wheather previous CLAS publication on etaprime photoproduction cross section was correct or not.

As one can see from figure on page 6 of Cathrina’s talk cross sections extracted 
using Q-factor on etaprime is very similar to the published results based on g11 
data. However, when Q-factor was applied to the \eta, see page 16, the cross 
sections differ significantly.

This raises also a question how  will this affect the f1 cross section if you apply Q factor to the eta.

In a paper draft you reproduced published cross section on etaprime, which proves that 
in both analyses signal of etaprime was extracted from the missing mass of the proton only, leaving contribution from the background under the eta peak unaddressed.
An application of the Q-factor will affect also t-dependence of both etaprime and f1 mesons and affect subsequent discussion about the nature of f1 etc.

I would recommend to withold a paper draft until these questions are clarified.

Best regards,
Moskov. 

Prof. Moskov Amaryan
Department of Physics
Old Dominion University
4600 Elkhorn Avenue
Norfolk, VA 23529

phone:757-683-4614