49,671 research outputs found

### Ground State Baryons in U(12) Scheme

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

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

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

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

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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