305 research outputs found

    Photoproduction of Pseudoscalar Mesons

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    Experiments that study the photoproduction of pseudoscalar mesons; pions, etas and kaons, have the potential to increase our knowledge of baryon and hyperon resonance properties. Recent experiments at JLab, Mainz, GRAAL, and Bonn are beginning to produce results in the form of polarization and asymmetry measurements and determinations of the differential and integrated cross sections. These new data are essential to the performance of Partial-Wave Analyses that are less model dependent and coupled-channels calculations that incorporate unitarity dynamically,combining hadronic reaction channels together with electromagnetic processes. This approach is necessary to extract resonance properties and may lead to the identification of missing, but predicted, resonances. Some recent experimental and phenomenological results for single and double pseudoscalar meson photoproduction are discussed.Comment: 4 pages, 4 figures, Proceedings of Particles and Nuclei, PANIC2002, Osaka, Japan, Sept.30-Oct.4, 200

    Extraction of the πNN\pi NN coupling constant from NN scattering data

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    We reexamine Chew's method for extracting the πNN\pi NN coupling constant from np differential cross section measurements. Values for this coupling are extracted below 350 MeV, in the potential model region, and up to 1 GeV. The analyses to 1~GeV have utilized 55 data sets. We compare these results to those obtained via χ2\chi^2 mapping techniques. We find that these two methods give consistent results which are in agreement with previous Nijmegen determinations.Comment: 12 pages of text plus 2 figures. Revtex file and postscript figures available via anonymous FTP at ftp://clsaid.phys.vt.edu/pub/n

    Model dependence of single-energy fits to pion photoproduction data

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    Model dependence of multipole analysis has been explored through energy-dependent and single-energy fits to pion photoproduction data. The MAID energy-dependent solution has been used as input for an event generator producing realistic pseudo data. These were fitted using the SAID parametrization approach to determine single-energy and energy-dependent solutions over a range of lab photon energies from 200 to 1200 MeV. The resulting solutions were found to be consistent with the input amplitudes from MAID. Fits with a χ\chi-squared per datum of unity or less were generally achieved. We discuss energy regions where consistent results are expected, and explore the sensitivity of fits to the number of included single- and double-polarization observables. The influence of Watson's theorem is examined in detail.Comment: 12 pages, 8 figure

    Multipole Amplitudes of Pion Photoproduction on Nucleons up to 2GeV within Dispersion Relations and Unitary Isobar Model

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    Two approaches for analysis of pion photo- and electroproduction on nucleons in the resonance energy region are checked at Q2=0Q^2=0 using the results of GWU(VPI) partial-wave analysis of photoproduction data. The approaches are based on dispersion relations and unitary isobar model. Within dispersion relations good description of photoproduction multipoles is obtained up to W=1.8GeVW=1.8 GeV. Within unitary isobar model, modified with increasing energy by incorporation of Regge poles, and with unified Breit-Wigner parametrization of resonance contributions, good description of photoproduction multipoles is obtained up to W=2GeVW=2 GeV.Comment: 23 pages, LaTe

    Coherent bubble-sum approximation for coupled-channel resonance scattering

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    For coupled-channel resonance scattering we derive a model with a closed form solution for the TT-matrix that satisfies unitarity and analyticity. The two-channel case is handled explicitly for an arbitrary number of resonances. The method focuses on the expansion of the transition matrix elements, Γ(s)\Gamma(s), in known analytical functions. The appropriate hadronic form factors and the related energy shifts can be determined from the scattering data. The differences between this method and the KK-matrix and the Breit-Wigner approximation are illustrated in the case of the S11S_{11} resonances S11(1535)S_{11}(1535) and S11(1650)S_{11}(1650).Comment: 8 pages, 1 figure, code available from http://www.phyast.pitt.edu/~norbertl/bubblegum2

    Angle-dependent normalization of neutron-proton differential cross sections

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    Systematic errors in the database of npnp differential cross sections below 350 MeV are studied. By applying angle-dependent normalizations with the help of the energy-dependent Nijmegen partial-wave analysis PWA93 the χ2\chi^2-values of some seriously flawed data sets can be reduced significantly at the expense of a few degrees of freedom. It turns out that in these special cases the renormalized data sets can be made statistically acceptable such that they do not have to be discarded any longer in partial-wave analyses of the two-nucleon scattering data.Comment: 11 pages, 1 figure; expanded versio

    Delta rho pi interaction leading to N* and Delta* resonances

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    We have performed a calculation for the three body Δρπ\Delta \rho \pi system by using the fixed center approximation to Faddeev equations, taking the interaction between Δ\Delta and ρ\rho, Δ\Delta andπ\pi, and ρ\rho and π\pi from the chiral unitary approach. We find several peaks in the modulus squared of the three-body scattering amplitude, indicating the existence of resonances, which can be associated to known I=1/2,3/2I=1/2, 3/2 and JP=1/2+,3/2+J^P=1/2^+, 3/2^+ and 5/2+5/2^+ baryon states.Comment: Presented at the 21st European Conference on Few-Body Problems in Physics, Salamanca, Spain, 30 August - 3 September 201

    On the pion-nucleon coupling constant

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    In view of persisting misunderstanding about the determination of the pion-nucleon coupling constants in the Nijmegen multienergy partial-wave analyses of pp, np, and pbar-p scattering data, we present additional information which may clarify several points of discussion. We comment on several recent papers addressing the issue of the pion-nucleon coupling constant and criticizing the Nijmegen analyses.Comment: 19 pages, Nijmegen preprint THEF-NYM-92-0
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