49,671 research outputs found

    Ground State Baryons in U(12) Scheme

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    The properties of ground-state baryons of light-quarks are investigated in U(12)-classification scheme of hadrons, recently proposed by us. In U(12), in addition to the ordinary 56 of SU(6)SF, the existence of the extra 56 with positive-parity and 70 with negative-parity appear as ground-states in lower mass region. The N(1440), Lambda(1600) and Sigma(1660) have the plausible properties of masses and strong decay widths as the flavor-octet of extra 56, while the ordinary radially-excited octet states are expected not to be observed as resonances because of their large predicted widths of the decays to extra 70 baryons. The extra 70 baryons are not observed directly as resonances for the same reason, except for only the Lambda(1406), of which properties are consistently explained through the singlet-octet mixing. The baryon properties in lower mass regions are consistently explained in U(12) scheme.Comment: 11 pages, uses elsart.cl

    Covariant Description of Composite Meson Systems and Chiral Symmetry

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    Assuming the spin-independence for confining force, we give a covariant quark representation of general composite meson systems with definite Lorentz transformation properties. For benefit of this representation we are able to deduce automatically the transformation rules of composite mesons for general symmetry operations from those of constituent (exciton) quarks. Applying this we investigate especially physical implication of chiral symmetry for the meson systems, and point out a possibility of existence of new meson multiplets.Comment: talk given in HADRON'99 in Beijing, August 1999. 4 pages, uses espcrc1.st

    Light sigma-Meson Production in Excited Upsilon Decay Processes I: Analyses

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    We analyze the pi pi production amplitudes in the excited Upsilon decay processes, Upsilon(2S)-->Upsilon(1S)pi+pi-, Upsilon(3S)-->Upsilon(1S)pi+pi- and Upsilon(3S)-->Upsilon(2S)pi+pi-, and the pi pi and KKbar production amplitudes in the charmonium decay processes, psi(2S)-->J psi pi+pi- and J psi-->phi pi+pi-, phi K+K-. The amplitudes are parametrized by the sum of Breit-Wigner amplitudes for the sigma and the other relevant particles and of the direct 2pi-production amplitude, following the VMW method. All the pi pi (and KKbar) invariant mass spectra are reproduced well with the sigma Breit-Wigner amplitude by using the common parameters, m_sigma=526^(+48)_(-37) MeV and Gamma_sigma =301^(+145)_(-100) MeV, which is almost consistent with the values obtained in our previous phase shift analyses. This strongly suggests the existence of light sigma-meson.Comment: proc. of ``Possible Existence of sigma-Meson and Its Implication to Hadron Physics," YITP, Kyoto, June 12--14, 2000. 5 pages, uses ptptex.st

    Relation between Scattering and Production Amplitude - Case of Intermediate \sigma-Particle in \pi\pi-System

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    The relation between scattering and production amplitudes are investigated, using a simple field theoretical model, from the general viewpoint of unitarity and the applicability of final state interaction(FSI-) theorem. The IA-method and VMW-method, which are applied to our phenomenological analyses suggesting the \sigma-existence, are obtained as the physical state representations of scattering and production amplitudes, respectively. Moreover, the VMW-method is shown to be an effective method to obtain the resonance properties from general production processes, while the conventional analyses based on the ``universality'' of \pi\pi-scattering amplitude are powerless for this purpose.Comment: Talk at HADRON'97, the 7th int. conf. on hadron spectroscopy, BNL, August 1997. 4 pages with no figur

    Covariant Classification Scheme of Hadrons

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    Starting from the multi-local Klein-Gordon equations with Lorentz-scalar squared-mass operator we give a covariant quark representation of the general composite mesons and baryons with definite Lorentz transformation property. The mass spectra satisfy the approximate symmetry under the tilde U(4) transformation group, including the chiral transformation as a subgroup, concerning the spinor freedom of light constituent quarks, and this symmetry predicts the existence of new type of chiral mesons and baryons out of the conventional framework in non-relativistic quark model: For example, for light qqbar systems, the scalar sigma- and axial-vector a_1-nonets, and for heavy-light Qqbar and qQbar systems the scalar and axial-vector mesons are predicted to exist as relativistic S-wave states besides the ordinary P-wave state mesons. The existence of two ``exotic'' 1^-+ meson nonets is predicted as the relativistic P-wave states in qqbar systems. For light quark baryons the extra 56 with positive parity and the extra 70 with negative parity of the static SU(6) are predicted to exist as the ground state chiral particles.Comment: proc. of "Hadron '01," Protvino, Russia, Aug, 2001. 10 pages, uses ptptex.st
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