[Theory-seminars] Reminder: Theory Seminar TODAY

[Christopher Thomas]

Dear all,

A reminder that there's a theory seminar this afternoon (Monday) at 1pm 
in L104:

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Monday February 22nd
1pm
L104

*The phase and pole structure of N*(1535) and the issue of σ_n/σ_p in 
η-photoproduction within UχPT*

Kanzo Nakayama (University of Georgia)

The nature of some baryonic resonances is still an unresolved issue. The 
case of the N*(1535) is particularly interesting in this respect due to 
the nearby eta-N threshold and interference with the N*(1650). The 
N*(1535) has been described as a threshold effect, as a genuine 3-quark 
resonance, or as dynamically generated from the interaction of the octet 
of baryons with the octet of mesons. In the scheme of dynamical 
generation, predictions for the interaction of the N*(1535) with the 
photon can be made. In this study, we simultaneously analyze the role of 
the N*(1535) in the pi-N --> pi-N and the gamma-N --> pi-N  reactions 
within a UxPT approach and compare to the respective amplitudes from 
partial wave analysis.

Within the same approach, we also address the issue of the recently 
discovered enhancement of eta photoproduction on the quasi-free neutron 
at energies around sqrt s ~ 1.67 GeV. The quasi-free cross sections on 
proton and neutron, sigma_n and sigma_p, can be quantitatively 
explained. In this study, the main source for the peak in 
sigma_n/sigma_p is shown to be a coupled channel effect in S wave that 
explains the dip-bump structure in the gamma-n --> eta-n. This is a 
direct consequence of the underlying hadron dynamics which, in the 
present model, is driven by the Weinberg-Tomozawa contact interaction 
with a relatively strong coupling to the K-Lambda and K-Sigma channels 
through the SU(3) structure in conjunction with the Kaon decay constant 
of fK ≈ 113 MeV.

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A complete list of upcoming theory seminars and talks from previous
seminars are available from:
http://www.jlab.org/~thomasc/seminars/index.html

Thanks,
Christopher


-- 
Christopher Thomas

Jefferson Laboratory
12000 Jefferson Avenue
Suite #1
Newport News
VA 23606
USA

Tel: +1 (757) 269 7453
Email: thomasc at jlab.org