arXiv subjects

Shin Ishida

Publications and source records attributed to Shin Ishida.

At least 37 records · Page 2Linked to original sources

arXiv2002

Possible Evidence for a Chiral Particle B_0chi, Scalar Meson in the B Meson System

In the covariant level-classification scheme of hadrons proposed recently, the existence of "chiral particles", scalar and axial-vector mesons as the partners of the ground-state pseudo-scalar and vector mesons, respectively, were predicted in the D meson and B meson systems, realizing a linear representation of chiral symmetry. In this work we reanalyze the B0 pi mass spectra through Z0 decays to show a possibility for the scalar B_0chi.

hep-ph↗

arXiv2002

U(12) A New Symmetry Possibly Realizing in Hadron Spectroscopy

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 phenomenologically observed hadron mass spectra is pointed out to satisfy possibly the approximate symmetry under the tilde U(4) transformation group concerning the spinor freedom of light constituent quarks, including the chiral transformation as a subgroup. This symmetry predicts the existence of new type of chiral mesons and baryons out of the conventional framework in non-relativistic quark model: For light q qbar systems, the scalar sigma- and axial-vector a1-nonets are predicted to exist as relativistic S-wave states besides the ordinary P-wave state mesons. Two "exotic" JPC=1-+ mesons are predicted to exist as relativistic P-wave states, which are possibly assigned as pi1(1400) and pi1(1600). 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.

hep-ph↗

arXiv2001

Possible Evidence for a Chiral Axial-Vector State in the D Meson System

We reanalyze the D^{*+} pi^- mass spectrum from CLEO II by the VMW method in order to examine the existence of a chiral axial-vector state, which is predicted in a covariant level-classification scheme recently proposed, other than normal orbitally-excited P-wave states in the D meson system. A result of the present analysis seems to suggest that there exists an extra axial-vector meson, in addition to the two normal ones, in a similar mass region.

hep-ph↗

arXiv2001

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.

hep-ph↗

arXiv2001

The sigma-Meson Production in Excited Upsilon Decay Processes

We analyze the pipi production amplitudes in the excited Upsilon decay processes, Upsilon (2S) to Upsilon (1S)pi^+pi^-, Upsilon (3S) to Upsilon (1S)pi^+pi^- and Upsilon (3S) to Upsilon (2S)pi^+pi^-, and the pipi and KKbar production amplitudes in the charmonium decay processes, psi (2S) to Jpsi pi^+pi^- and Jpsi to phi pi^+pi^-, phi K^+K^-, including the possible effect of light sigma production. 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 pipi (and KKbar mass spectra are reproduced well with the obtained values of sigma-parameters, m_sigma =526(+48,-37)MeV and Gamma_sigma =301(+145,-100)MeV, which is almost consistent with the values in our previous phase shift analyses.

hep-ph↗

arXiv2001

Property of Chiral Scalar and Axial-Vector Mesons in Heavy-Light Quark Systems

Recently we have proposed a new level-classification scheme of hadrons with a manifestly covariant framework. In this scheme the requirement of chiral symmetry on the light quark leads to a prediction of existence of new type of scalars X_B, X_D and axial-vectors X_B^*,X_D^* as the chiral partners of ground state pseudoscalar B,D and vector B^*,D^* mesons, respectively. They belong to ``relativistic S-wave states,'' and are discriminated from the conventional P-wave mesons with j_q=1/2 appearing in the heavy quark effective theory. In this talk we examine the properties of these chiral mesons: The mass-splittings between the respective chiral partners are predicted to be equal, and the decay widths of one pion emission of X_B, X_D, X_B^* and X_D^* are to take the same value due to both chiral and heavy quark symmetries. Some experimental indications for existence of X_B and X_D^* are also given, which are consistent with the above prediction.

hep-ph↗

arXiv2001

Confirmation of sigma(450--600)-Meson in Upsilon' to Upsilon pipi and Other pipi-Production Processes

Applying the effective amplitude, which is evidently consistent with general constraints from chiral symmetry, the pipi spectra in the relevant processes are analyzed, leading to a strong evidence for existence of the light sigma meson. It is also pointed out that the pipi scattering process, which had been one of the main sources for PDG table for these many years, is, in principle, exceptionally difficult to investigate the property of sigma-meson.

hep-ph↗

arXiv2001

Property of Chiral Scalar and Axial-Vector Mesons in Heavy-Light Quark System

We investigate the properties of new scalar X_B, X_D and axial-vector X_B*, X_D* mesons, which are recently predicted, in the covariant meson-classification scheme, to exist as the partners of ground-state pseudoscalar B, D and vector B*, D* mesons, respectively, realizing a linear representation of chiral symmetry for the light quark component in heavy-light-quark meson system. The mass splittings between the respective chiral partners are shown to be equal, and the decay widths of one pion emission of X_B, X_D, X_B* and X_D* become to have a common value, due to chiral and heavy quark symmetry.

hep-ph↗

arXiv2000

Production of 3pi0 and eta 2pi0 from pi-p Collision in GAMS Experiment

The data on the pi- p --> M0 n, with M0 = pi0 pi0 pi0 or pi0 pi0 eta obtained in the GAMS experiment may be useful to study the sigma(400--700) and a_1^chi (1000), which can be taken as chiral partners of pi and rho, respectively. A preliminary analysis for 3pi0 invariant mass spectra gives a support for the assumed a_1^chi with a mass of 930 MeV and Gamma = 170 MeV.

hep-ph↗

arXiv2000

S-matrix Bases and Relation between pi pi Scattering and Production Amplitudes

It is stated that the requirement of unitarity and of analyticity should be made on the S-matrix elements with right bases, and the ``universality argument" made with the bases, which do not regard quark physical picture, is not right. Accordingly the result of the conventional analyses of the pi pi production amplitudes following to this argument, leading to non-existence of the light sigma-meson, is proved to lose its theoretical bases.

hep-ph↗

arXiv2000

Light sigma-Meson Production in Excited Upsilon Decay Processes II: Theoretical Investigation

The results of analyses obtained in Part I are examined from the viewpoint of chiral symmetry. The mass spectra of pi pi system are widely believed to be suppressed generally near the threshold, because of the derivative coupling property of Nambu-Goldstone pi meson. However, this suppression does not hold in the processes with large energy release, and the steep increase from the pi pi threshold observed in the transition Upsilon (3S-->1S) is shown to be consistent with general constraints from chiral symmetry.

hep-ph↗

arXiv2000

Covariant Level-Classification Scheme and Chiral Symmetry

Starting from the bi-local Klein-Gordon Equation with spin-independent squared-mass operator, 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 present a covariant level-classification scheme, leading to a possible existence of new meson multiplets of "chiralons."

hep-ph↗

arXiv2000

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.

hep-ph↗

arXiv2000

Effect of light sigma-meson Production in ppbar --> 3 pi0 at rest

The pi0 pi0 mass spectra and angular distributions around KKbar -threshold and at 1.5 GeV in ppbar (at rest) --> 3 pi0 in the Crystal Barrel experiment are reanalyzed by applying the new method, which is consistent with unitarity of S-matrix and expressed directly by resonance parameters. The effects of light sigma-meson production are clearly seen to improve the fit with sigma, in comparing with the fit without sigma.

hep-ph↗

arXiv2000

Covariant Quark-Representation 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.

hep-ph↗

arXiv2000

Semi-Leptonic B Meson Decays to Excited D Mesons in the Covariant Oscillator Quark Model

The spectra and branching ratios of the weak semi-leptonic B meson decays to the first excited D mesons are predicted, taking into account the confined effects of quarks using the covariant oscillator quark model (COQM). In the COQM the same relation between general weak transition form factors as that in HQET is derived, and the concrete form of the Isgur-Wise function is given with no free parameters. Our results are somewhat different from those of other models. The present experimental data are not sufficient for comparison.

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arXiv2000

Covariant Description of Composite Meson Systems and Chiral Symmetry

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arXiv1999

Effect of sigma(600)-Production in pp_bar to 3pi0 at rest

The pi0 pi0 mass spectra and angular distributions around KK_bar-threshold and at 1.5 GeV in pp_bar(at rest) to 3pi0 in the Crystal Barrel experiment are reanalyzed by applying the new method, which is consistent with unitarity of S-matrix and expressed directly by resonance parameters. The effects of light sigma-meson production are clearly seen to improve the fit with sigma, in comparing with the fit without sigma.

hep-ph↗