2,704 research outputs found

    The Glueball in a Chiral Linear Sigma Model with Vector Mesons

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    We present a two-flavour linear sigma model with global chiral symmetry and (axial-)vector mesons as well as an additional glueball degree of freedom. We study the structure of the well-established scalar resonances f0(1370) and f0(1500): by a fit to experimentally known decay widths we find that f0(1370) is predominantly a \bar{q}q state and f0(1500) is predominantly a glueball state. The overall phenomenology of these two resonances can be well described. Other assignments for our mixed quarkonium-glueball states are also tested, but turn out to be in worse agreement with the phenomenology. As a by-product of our analysis, the gluon condensate is determined.Comment: 8 page

    Role of heavy-meson exchange in pion production near threshold

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    Recent calculations of ss-wave pion production have severely underestimated the accurately known ppppπ0pp\rightarrow pp\pi^0\ total cross section near threshold. In these calculations, only the single-nucleon axial-charge operator is considered. We have calculated, in addition to the one-body term, the two-body contributions to this reaction that arise from the exchange of mesons. We find that the inclusion of the scalar σ\sigma-meson exchange current (and lesser contributions from other mesons) increases the cross section by about a factor of five, and leads to excellent agreement with the data. The results are neither very sensitive to changes in the distorting potential that generates the NNNN wave function, nor to different choices for the meson-nucleon form factors. We argue that ppppπ0pp\rightarrow pp\pi^0\ data provide direct experimental evidence for meson-exchange contributions to the axial current.Comment: 28 Pages, IU-NTC #93-0

    Dependence of pp->pp pi0 near Threshold on the Spin of the Colliding Nucleons

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    A polarized internal atomic hydrogen target and a stored, polarized beam are used to measure the spin-dependent total cross section Delta_sigma_T/sigma_tot, as well as the polar integrals of the spin correlation coefficient combination A_xx-A_yy, and the analyzing power A_y for pp-> pp pi0 at four bombarding energies between 325 and 400 MeV. This experiment is made possible by the use of a cooled beam in a storage ring. The polarization observables are used to study the contribution from individual partial waves.Comment: 6 pages, 1 table, 4 figures, corrected equations 2 and

    A search for two body muon decay signals

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    Lepton family number violation is tested by searching for μ+e+X0\mu^+\to e^+X^0 decays among the 5.8×108\times 10^8 positive muon decay events analyzed by the TWIST collaboration. Limits are set on the production of both massless and massive X0X^0 bosons. The large angular acceptance of this experiment allows limits to be placed on anisotropic μ+e+X0\mu^+\to e^+X^0 decays, which can arise from interactions violating both lepton flavor and parity conservation. Branching ratio limits of order 10510^{-5} are obtained for bosons with masses of 13 - 80 MeV/c2^2 and with different decay asymmetries. For bosons with masses less than 13 MeV/c2^{2} the asymmetry dependence is much stronger and the 90% limit on the branching ratio varies up to 5.8×1055.8 \times 10^{-5}. This is the first study that explicitly evaluates the limits for anisotropic two body muon decays.Comment: 7 pages, 5 figures, 2 tables, accepted by PR