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Title: Dynamical coupled-channel model of meson production reactions in the nucleon resonance region.

Abstract

A dynamical coupled-channel model is presented for investigating the nucleon resonances (N*) in the meson production reactions induced by pions and photons. Our objective is to extract the N* parameters and to investigate the meson production reaction mechanisms for mapping out the quark-gluon substructure of N* from the data. The model is based on an energy-independent Hamiltonian which is derived from a set of Lagrangians by using a unitary transformation method. The constructed model Hamiltonian consists of (a) {Gamma}V for describing the vertex interactions N*{leftrightarrow}MB,{pi}{pi}N with MB={gamma}N,{pi}N,{epsilon}N,{pi}{Delta},{rho}N,{sigma}N, and {rho}{leftrightarrow}{pi}{pi} and {sigma}{leftrightarrow}{pi}{pi}, (b) v22 for the non-resonant MB{yields}M'B' and {pi}{pi}{yields}{pi}{pi} interactions, (c) vMB,{pi}{pi}N for the non-resonant MB{yields}{pi}{pi}N transitions, and (d) v{pi}{pi}N,{pi}{pi}N for the non-resonant {pi}{pi}N{yields}{pi}{pi}N interactions. By applying the projection operator techniques, we derive a set of coupled-channel equations which satisfy the unitarity conditions within the channel space spanned by the considered two-particle MB states and the three-particle {pi}{pi}N state. The resulting amplitudes are written as a sum of non-resonant and resonant amplitudes such that the meson cloud effects on the N* decay can be explicitly calculated for interpreting the extracted N* parameters in terms of hadron structure calculations. We present and explain in detail a numerical method based on amore » spline-function expansion for solving the resulting coupled-channel equations which contain logarithmically divergentone-particle-exchange driving terms {sup (E)}{sub M B, M' B'} resulted from the {pi}{pi}N unitarity cut. This method is convenient, and perhaps more practical and accurate than the commonly employed methods of contour rotation/deformation, for calculating the two-pion production observables. For completeness in explaining our numerical procedures, we also present explicitly the formula for efficient calculations of a very large number of partial-wave matrix elements which are the input to the coupled-channel equations. Results for two pion photo-production are presented to illustrate the dynamical consequence of the one-particle-exchange driving term Z{sup (E)}{sub M B, M' B'} of the coupled-channel equations. We show that this mechanism, which contains the effects due to {pi}{pi}N unitarity cut, can generate rapidly varying structure in the reaction amplitudes associated with the unstable particle channels {pi}{Delta}, {rho}N, and {sigma}N, in agreement with the analysis of Aaron and Amado [Phys. Rev. D13 (1976) 2581]. It also has large effects in determining the two-pion production cross sections. Our results indicate that cautions must be taken to interpret the N* parameters extracted from using models which do not include {pi}{pi}N cut effects. Strategies for performing a complete dynamical coupled-channel analysis of all of available data of meson photo-production and electro-production are discussed.« less

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); JAPAN SOCIETY FOR PROMOTION OF SCIENCE
OSTI Identifier:
914942
Report Number(s):
ANL/PHY/JA-58490
Journal ID: ISSN 0370-1573; PRPLCM; TRN: US0804854
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys. Rep.; Journal Volume: 439; Journal Issue: 5-6 ; Feb. 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; MESONS; NUCLEONS; PRODUCTION; RESONANCE

Citation Formats

Matsuyama, A., Sato, T., Lee, T.-S. H., Physics, Shizuoka Univ., Osaka Univ., and Jefferson Lab. Dynamical coupled-channel model of meson production reactions in the nucleon resonance region.. United States: N. p., 2007. Web. doi:10.1016/j.physrep.2006.12.003.
Matsuyama, A., Sato, T., Lee, T.-S. H., Physics, Shizuoka Univ., Osaka Univ., & Jefferson Lab. Dynamical coupled-channel model of meson production reactions in the nucleon resonance region.. United States. doi:10.1016/j.physrep.2006.12.003.
Matsuyama, A., Sato, T., Lee, T.-S. H., Physics, Shizuoka Univ., Osaka Univ., and Jefferson Lab. Thu . "Dynamical coupled-channel model of meson production reactions in the nucleon resonance region.". United States. doi:10.1016/j.physrep.2006.12.003.
@article{osti_914942,
title = {Dynamical coupled-channel model of meson production reactions in the nucleon resonance region.},
author = {Matsuyama, A. and Sato, T. and Lee, T.-S. H. and Physics and Shizuoka Univ. and Osaka Univ. and Jefferson Lab.},
abstractNote = {A dynamical coupled-channel model is presented for investigating the nucleon resonances (N*) in the meson production reactions induced by pions and photons. Our objective is to extract the N* parameters and to investigate the meson production reaction mechanisms for mapping out the quark-gluon substructure of N* from the data. The model is based on an energy-independent Hamiltonian which is derived from a set of Lagrangians by using a unitary transformation method. The constructed model Hamiltonian consists of (a) {Gamma}V for describing the vertex interactions N*{leftrightarrow}MB,{pi}{pi}N with MB={gamma}N,{pi}N,{epsilon}N,{pi}{Delta},{rho}N,{sigma}N, and {rho}{leftrightarrow}{pi}{pi} and {sigma}{leftrightarrow}{pi}{pi}, (b) v22 for the non-resonant MB{yields}M'B' and {pi}{pi}{yields}{pi}{pi} interactions, (c) vMB,{pi}{pi}N for the non-resonant MB{yields}{pi}{pi}N transitions, and (d) v{pi}{pi}N,{pi}{pi}N for the non-resonant {pi}{pi}N{yields}{pi}{pi}N interactions. By applying the projection operator techniques, we derive a set of coupled-channel equations which satisfy the unitarity conditions within the channel space spanned by the considered two-particle MB states and the three-particle {pi}{pi}N state. The resulting amplitudes are written as a sum of non-resonant and resonant amplitudes such that the meson cloud effects on the N* decay can be explicitly calculated for interpreting the extracted N* parameters in terms of hadron structure calculations. We present and explain in detail a numerical method based on a spline-function expansion for solving the resulting coupled-channel equations which contain logarithmically divergentone-particle-exchange driving terms {sup (E)}{sub M B, M' B'} resulted from the {pi}{pi}N unitarity cut. This method is convenient, and perhaps more practical and accurate than the commonly employed methods of contour rotation/deformation, for calculating the two-pion production observables. For completeness in explaining our numerical procedures, we also present explicitly the formula for efficient calculations of a very large number of partial-wave matrix elements which are the input to the coupled-channel equations. Results for two pion photo-production are presented to illustrate the dynamical consequence of the one-particle-exchange driving term Z{sup (E)}{sub M B, M' B'} of the coupled-channel equations. We show that this mechanism, which contains the effects due to {pi}{pi}N unitarity cut, can generate rapidly varying structure in the reaction amplitudes associated with the unstable particle channels {pi}{Delta}, {rho}N, and {sigma}N, in agreement with the analysis of Aaron and Amado [Phys. Rev. D13 (1976) 2581]. It also has large effects in determining the two-pion production cross sections. Our results indicate that cautions must be taken to interpret the N* parameters extracted from using models which do not include {pi}{pi}N cut effects. Strategies for performing a complete dynamical coupled-channel analysis of all of available data of meson photo-production and electro-production are discussed.},
doi = {10.1016/j.physrep.2006.12.003},
journal = {Phys. Rep.},
number = 5-6 ; Feb. 2007,
volume = 439,
place = {United States},
year = {Thu Feb 01 00:00:00 EST 2007},
month = {Thu Feb 01 00:00:00 EST 2007}
}
  • A dynamical coupled-channel model is presented for investigating the nucleon resonances (N*) in the meson production reactions induced by pions and photons. Our objective is to extract the N* parameters and to investigate the meson production reaction mechanisms for mapping out the quark-gluon substructure of N* from the data. The model is based on an energy-independent Hamiltonian which is derived from a set of Lagrangians by using a unitary transformation method.
  • As a first step to analyze the electromagnetic meson production reactions in the nucleon resonance region, the parameters of the hadronic interactions of a dynamical coupled-channel model, developed in {\it Physics Reports 439, 193 (2007)}, are determined by fitting the empiricalmore » $$\pi N$$ elastic scattering amplitudes of SAID up to 2 GeV. The channels included in the calculations are $$\pi N$$, $$\eta N$$ and $$\pi\pi N$$ which has $$\pi\Delta$$, $$\rho N$$, and $$\sigma N$$ resonant components. The non-resonant meson-baryon interactions of the model are derived from a set of Lagrangians by using a unitary transformation method. One or two bare excited nucleon states in each of $S$, $P$, $D$, and $F$ partial waves are included to generate the resonant amplitudes in the fits. The predicted total cross sections of $$\pi N$$ reactions and $$\pi N\rightarrow \eta N$$ reactions are in good agreement with the data. Applications of the constructed model in analyzing the electromagnetic meson production data as well as the future developments are discussed.« less
  • As a first step to analyze the electromagnetic meson production reactions in the nucleon resonance region, the parameters of the hadronic interactions of a dynamical coupled-channels model, developed in Physics Reports 439, 193 (2007), are determined by fitting the {pi}N-scattering data. The channels included in the calculations are {pi}N,{eta}N, and {pi}{pi}N, which has {pi}{delta},{rho}N, and {sigma}N resonant components. The nonresonant meson-baryon interactions of the model are derived from a set of Lagrangians by using a unitary transformation method. One or two bare excited nucleon states in each of S,P,D, and F partial waves are included to generate the resonant amplitudesmore » in the fits. The parameters of the model are first determined by fitting as much as possible the empirical {pi}N elastic-scattering amplitudes of SAID up to 2 GeV. We then refine and confirm the resulting parameters by directly comparing the predicted differential cross section and target polarization asymmetry with the original data of the elastic {pi}{sup {+-}}p{yields}{pi}{sup {+-}}p and charge-exchange {pi}{sup -}p{yields}{pi}{sup 0}n processes. The predicted total cross sections of {pi}N reactions and {pi}N{yields}{eta}N reactions are also in good agreement with the data. Applications of the constructed model in analyzing the electromagnetic meson production data as well as the future developments are discussed.« less
  • We construct a unitary Deck model with coupled K*..pi.. and Krho channels, including only one resonance in the Q region. Adjusting the resonance parameters, we achieve a satisfactory description of the experimental phase variations and the structure in the mass spectra. The resonance is determined to belong to the J/sub P//sub C/=1/sup + -/ SU(3) octet, and is thus the Q/sub B/. The relative coupling strength K*..pi../Krho is approx.2/3. (AIP)
  • A unitary coupled-channel effective Lagrangian model is applied to the combined analysis of the ({pi},{gamma})N{yields}K{lambda} reactions in the energy region up to 2 GeV. To constrain the resonance couplings to the K{lambda} final state the recent photoproduction data obtained by the SAPHIR, Spring-8, and CLAS groups are included in the calculations. The main resonance contributions to the process stem from the S{sub 11}(1650),P{sub 13}(1720), and P{sub 13}(1900) states. The second peak at 1.9 GeV seen in the photoproduction cross-section data is described as a coherent sum of the resonance and background contributions. The prediction for the beam polarization observable ismore » presented.« less