Browsing by Author "Workman, Ronald L."

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    Comment on "Evidence for Narrow Baryon Resonances in Inelastic ρρ Scattering"
    L'Vov, A. I.; Workman, Ronald L. (American Physical Society, 1998-08-10)
    In a recent Letter [1], Tatischeff et al. claimed evidence for three neutral baryon resonances N* between the nucleon and the Δ(1232). Two of these have masses M = 1004 and 1044 MeV below mN + mπ and thus their widths (Γ = ­4 to 15 MeV) are radiative. The third resonance M = 1094 MeV) also might have a radiative decay. All of the resonances have to contribute to Compton scattering on the nucleon and result in peaks at energies Eγ 68, 112, and 169 MeV, respectively, which were never observed on protons [2–5] or neutrons [6,7] loosely bound in the deuteron. Since constraints of this type are very sensitive and were not analyzed in the Letter, we give estimates...
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    Delta isobar masses, large N-c relations, and the quark model
    Capstick, S.; Workman, Ronald L. (American Physical Society, 1999-01-01)
    Motivated by recent remarks on the Delta(+) mass and comparisons between the quark model and relations based on large-iri, with perturbative flavor breaking, two sets of Delta masses consistent with these constraints are constructed. These two sets, based either on an experimentally determined mass splitting or a quark model of isospin symmetry breaking, are shown to be inconsistent. The model dependence of this inconsistency is examined, and suggestions for improved experiments are made. An explicit quark model calculation and mass relations based on the large-N-c limit with perturbative flavor breaking are compared. The expected level of accuracy of such relations is realized in the quark model, except for mass relations derived by combining others which correspond to different SU(6) representations. It is shown that the Delta(0) and Delta(++) pole masses and Delta(0) - Delta(+) = (Delta(-) - Delta(++))/3 similar or equal to 1.5 MeV are more consistent with model expectations than the analogous Breit-Wigner masses and their splittings. [S0556-2821(99)02301-2].
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    Energies and residues of the nucleon resonances N(1535) and N(1650)
    Arndt, R. A.; Green, A. M.; Workman, Ronald L.; Wycech, S. (American Physical Society, 1998-12)
    We extract pole positions for the N(1535) and N(1650) resonances using two different models. The positions are determined from fits to different subsets of the existing pi N --> pi N, pi N --> eta N, and gamma p --> eta p data and found to be 1510(10)-i85(15)MeV and 1660(10)-i70(10)MeV, when the data is described in terms of two poles. Sensitivity to the choice of fitted data is explored. The corresponding pi pi and eta eta residues of these poles are also extracted. [S0556-2813(98)07612-2].
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    Pole versus Breit-Wigner resonance description of the orbitally excited baryons
    Workman, Ronald L. (American Physical Society, 1999-06)
    We consider the masses used in recent studies involving the nonstrange sector of the l = 1 baryons. The use of T-matrix and K-matrix poles versus the conventional Breit-Wigner masses is discussed within the context of a large-N-c fitting scheme. [S0556-2813(99)01206-6].
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    A Unified Analysis of the B = 2 System
    Oh, Chang-Heon (Virginia Tech, 1997-04-23)
    Results are presented for a unified analysis of the reactions pp → pp, πd → πd and πd → pp over the center-of-mass energy interval from pion threshold to approximately 2.4 GeV. These results for πd → pp and πd elastic scattering are superior to previous VPI analyses of these reactions. In particular, the overall phase in πd → pp has now been determined. Comparisons and predictions are made with previous (separate and unified) analyses of this two-baryon system. Several partial wave amplitudes show resonance-like behavior in these reactions.