[Hybrid baryons] s-p-wave interference

[Viktor Mokeev]

 Hi All,
 I still see a major challenge in evaluation of resonance/background interference in our case of W which is higher then old resonance region W<2.0 GeV, but still not high enough to assume the Regge dominance. This is the reason why it is problematic just to add background with any model phase from model not fit to the data.

 May be theorists can help us with ideas on evaluation resonance/background interference? In particular, could we get help employing FESR approach under development by JPAC? Best contribution can be the model amplitudes to which we can add the hybrid resonance contribution at the amplitude level.

   Best Regards,
                       Victor

----- Original Message -----
From: "burkert" <burkert at jlab.org>
To: "hybrid baryons" <hybrid_baryons at jlab.org>
Sent: Sunday, July 19, 2015 10:16:57 AM
Subject: [Hybrid baryons] s-p-wave interference

Hi all, 

At the last hybrid meeting we had some discussion on s-p-wave interference. 
I attached a slide that hopefully helps clarifying this aspect. 

Any J P =1/2 + and J P =1/2 - terms that overlap in energy will interfere and generate in the Legendre expansion shown on the slide a term that is proportional to cos(theta). In the example shown (from our CLAS publication Phys.Rev. C78 (2008) 045209; arXiv:0804.0447 [nucl-ex] ; Phys.Rev. C77 (2008) 015208 , arXiv:0709.1946 ) 
the interference of the Roper P11 p-wave multipoles (S1-, M1-) with s-wave multipoles (E0+, S0+) from the N(1535) and non-resonant terms generates a strong cos(theta) term, half of which is due to the resonant Roper contribution (difference between solid and dotted lines). Of course, at this Q 2 the Roper is a large amplitude and contributes to the total cross section also strongly, but that is not the case at some smaller Q 2 where the interference term is essential in extracting the Roper contribution. 

Any comments on this are appreciated. 

Cheers, 
Volker 



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