[Theory-seminars] Seminars Friday 18 Jan 9:00 am NOTE THE TIME!

[Alexei Prokudin]

Dear all,

we will have 3 seminars on Friday, Jan 18, starting from 9 am till 12 pm
CEBAF Center, Room L104


1 Speaker:   Alvin Stanza Kiswandhi

1 Title:   Near-threshold behavior of the cross section of $\gamma p \to 
\phi p$ and $\gamma d \to \phi p n$: A resonance interpretation

1 Abstract:  We study whether the nonmonotonic behavior found in the 
differential cross section of the phi-meson
photoproduction off the proton near threshold can be described by a 
resonance. Namely, we add a resonance to a model consisting of Pomeron 
and (pi, eta) exchange by fiat and see if, with a suitable assignment of 
spin and
parity, mass and width, as well as the coupling constants, one would be 
able to obtain a good description
to all the data reported by the LEPS Collaboration in the low-energy 
region. The resonant contribution is
evaluated by using an effective Lagrangian approach. We find that, with 
the assumption of a resonance with spin 3/2
of both parities, LEPS data can indeed be well described. The ratio of 
the helicity amplitudes A _{1/2}/A_{3/2} calculated from the resulting 
coupling constants is quite similar to that of D13(2120) listed by PDG. 
We also perform a consistency check by applying our results to 
incoherent phi-meson photoproduction off the deuteron and found that 
without fitting to the data, we found a very good agreement. Moreover, 
we also present a prediction on the single and double polarization 
observables with the hope of resolving the
ambiguity on the parity of the resonance.


2 speaker: Vincent Mathieu
2 title: TBA
2 abstract: TBA

3 speaker: Miguel Albaladejo (U. Murcia)

3 title: Non-perturbative methods and Chiral Perturbation Theory applied 
to Meson-Meson interactions

3 abstract:  In this seminar, I will discuss several hadronic 
interactions by means of non-perturbative techniques based on 
unitarization of amplitudes obtained from Chiral Perturbation Theory. 
First, I will discuss the scalar sector, $J^{PC}=0^{++}$, for which one 
needs to consider different meson-meson amplitudes. These are obtained 
from the unitarization of chiral amplitudes, avoiding {\it ad-hoc} 
parameterizations. We include the relevant channels up to $\sqrt{s}=$ 2 
GeV, so as to reproduce all the scalar resonances appearing up to that 
energy. Later, I will consider the scattering of scalar ($f_0,a_0$) and 
pseudoscalar ($\pi$, $K$, $\eta$, $\eta'$) mesons, in order to study the 
possible appearence of heavier pseudoscalar resonances. Given the 
dynamically generated nature of the light scalars, these amplitudes can 
also be obtained from Chiral Lagrangians. Finally, I will elaborate 
further on the issue of the nature of the $\sigma$ meson, by studying 
its quadratic scalar radius. Given the small value found for the latter, 
it can be argued that a four-quark picture for the latter is more 
appropiate than a molecular one.


A complete list of upcoming theory seminars and talks from previous
seminars is available from:
http://www.jlab.org/div_dept/theory/seminars/

Alexei, Alvaro and Carlos
JLab Theory Seminar Organizers

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 Alexei Prokudin                    | Tel:     +1 (757) 269 5385
 JLab Theory Center                 | Fax:     +1 (757) 269 7002
 12000 Jefferson Avenue             | E-mail:  prokudin at jlab.org
 Newport News, VA 23606             | https://userweb.jlab.org/~prokudin/
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