1,492 research outputs found
Two-Photon-Exchange Effects and Deformation
The two-photon-exchange (TPE) contribution in with
and small is calculated and its corrections to the ratios
of electromagnetic transition form factors and ,
are analysed. A simple hadronic model is used to estimate the TPE amplitude.
Two phenomenological models, MAID2007 and SAID, are used to approximate the
full cross sections which contain both the TPE and the
one-photon-exchange (OPE) contributions. The genuine the OPE amplitude is then
extracted from an integral equation by iteration. We find that the TPE
contribution is not sensitive to whether MAID or SAID is used as input in the
region with GeV.
It gives small correction to while for , the correction is
about -10\% at small and about at large for
GeV. The large correction from TPE at small must
be included in the analysis to get a reliable extraction of .Comment: Talk given at Conference:C16-07-2
Remarks on the complex branch points in pi-N scattering amplitude and the multiple poles structure of resonances
A simple heuristic argument to understand the existence of branch points in
the unphysical sheet for pi-N scattering amplitude is presented. It is based on
a hypothesis that the singularity structure of the pi-N scattering amplitude is
a smooth varying function of the pion mass. We find that, in general, multiple
poles structure of a resonance is a direct mathematical consequence when
additional Riemann surface is included in the study and the two-pole structure
found to correspond to the Roper resonance is a good example
P11 Resonances with Dubna-Mainz-Taipei Dynamical Model for pi-N Scattering and Pion Electromagnetic Production
We present the results on P11 resonances obtained with Dubna-Mainz-Taipei
(DMT) dynamical model for pion-nucleon scattering and pion electromagnetic
production. The extracted values agree well, in general, with PDG values. One
pole is found corresponding to the Roper resonance and two more resonances are
definitely needed in DMT model. We further find indication for a narrow P11
resonance at around 1700 MeV with a width of around 50 MeV in both pi-N and
gamma-pi reactions.Comment: Contribution to the Proceedings of NSTAR 2011 - The 8th International
Workshop on the Physics of Excited Nucleons, May 17-20, 2011, Thomas
Jefferson National Accelerator Facility, Newport News, Virginia US
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