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Shin Ishida

Publications and source records attributed to Shin Ishida.

54 records · Page 3Linked to original sources
arXiv1999

Weak Radiative Decay Lambda_b to Lambda gamma and Quark-Confined Effects in the Covariant Oscillator Quark Model

Motivated by the observation of the decay B to K* gamma by the CLEO collaboration, we have systematically analyzed the weak radiative decay Lambda_b to Lambda gamma, evaluating the confined effects of quarks in the covariant oscillator quark model. This decay process receives both short distance (electromagnetic penguins at the one loop level) the long distance contributions in the quark level. The long distance contributions are analyzed using the vector meson dominance (VMD) method. The estimated branching ratio is found to be 0.23 times 10^-5.

hep-ph↗
arXiv1999

Covariant Classification of q q bar-Meson Systems and Existence of New Scalar and Axial-Vector Mesons

The level classification of quark-antiquark systems is generally made by the LS-coupling scheme, resorting to the non-relativistic quark model. However, it has been well known that the pi-meson with the (L,S)=(0,0) shows also the properties as a Nambu-Goldstone boson in the case of spontaneous breaking of a relativistic symmetry, the chiral symmetry. In this talk I present a covariant classification scheme for describing both the non-relativistic and the relativistic q q bar-mesons and point out possibility for existence of the new scalar meson nonet (to be assigned to the sigma nonet) and also of the new axial-vector meson nonet, ``chiralons,'' which should be discriminated from the conventional ^3P_0 and ^3P_1 states, respectively.

hep-ph↗
arXiv1999

Controversies on and a Reasoning for Existence of the light sigma-particle

The light sigma-particle is, regardless of the strong criticism, reviving recently due to the works done from various sides. I review essential points of the controversies (especially related to our works) and of their answer: Conventionally a large concentration of the iso-scalar S-wave 2 pi events below 1 GeV (being, correctly, due to the sigma-production), which is observed in most of production processes, is interpreted as a mere background from the viewpoint of, so called, universality argument. However, I show, by resorting to a simple field theoretical model, that the argument is not correct and the production process has ``its own value'' independent of the scattering process. Thus it is suggested that the present index ``f_0(400-1200) or sigma'' in PDG'98 is to be changed as ``sigma(400-800)'' in the PDG 2000.

hep-ph↗
arXiv1999

Observed Properties of sigma-particle

Recently we obtained the evidence for the existence of sigma(600) meson, which had been sought but missing for a long time, by reanalyzing the I=0 S-wave pi pi scattering phase shift. The sigma-existence was also suggested through the analyses of pi pi production processes, pp central collision pp to pp pi^0 pi^0 and J/psi to omega pi pi decay. The observed properties through these works of sigma meson satisfy the mass and width relation of SU(2) linear sigma model. The physical origin of the repulsive background phase shift delta_{BG}, which was essential to lead to the sigma-existence in our phase shift analysis, is also due to the "compensating lambda phi^4-interaction" in linear sigma model. Furthermore in this talk the experimental property of the delta_{BG} is shown to be describable quantitatively in the framework of linear sigma model including rho-meson contribution.

hep-ph↗
arXiv1999

Exclusive Weak Radiative Decays of B Mesons in the Covariant Oscillator Quark Model

Exclusive weak radiative B meson decays are studied using the covariant oscillator quark model. The branching ratios for the processes B0 to K*0 gamma and B to K* gamma have been estimated. These are in reasonable agreement with the available experimental data. The calculation has been extended to the CKM-suppressed decay processes B- to rho- gamma and Bs to K*0 gamma .

hep-ph↗
arXiv1999

Non-leptonic Two-meson Decays of B-Mesons in the Covariant Oscillator Quark Model with Factorization Ansatz

Exclusive nonleptonic bottom meson decays are studied in the covariant osillator quark model using the factorization assumption. The main feature of this model is that it can simultaniously be applied to both heavy to heavy and heavy to light transitions, satisfying the constraints of the heavy quark effective theory (HQET) in the appropriate limit. The results obtained are in overall agreement with the present experimental data for various B decays.

hep-ph↗
arXiv1999

Hadronic Weak Decays of Lambda b Baryon in the Covariant Oscillator Quark Model

Cabibbo allowed two-body hadronic weak decays of Lambda b baryons are analyzed in the factorization approximation. We use the covariant oscillator quark model to evaluate the heavy to heavy and heavy to light form factors. When applied in the heavy quark limit, our form factors satisfy all the constraints imposed by heavy quark symmetry. The decay rates and up-down asymmetries for Lambda b baryon decaying into Lambda c +P(V) are calculated. It is found that the up-down asymmetry is negative in all these decay modes. Furthermore, the prediction Br(Lambda b to Lambda+J/psi)=2.49 times 10^-4 is consistent with the recent experimental data. Finally it is pointed out that the CKM-Wolfenstein parameter rho^2+eta^2, where eta is the CP phase, can be determined from the ratio of the widths Lambda b to Lambda bar D^0 and Lambda b to Lambda J/psi, independent of the QCD parameter. The value of (rho^2 +eta^2)^1/2 calculated in our model agrees very well with the value recently predicted by Rosner.

hep-ph↗
arXiv1998

Relation between Scattering and Production Amplitudes - concerning sigma Particle in pi pi System -

In a series of previous papers the present authors and collaborators have shown strong evidence for existence of the long-sought sigma-particle by analyzing the pi pi-scattering and pi pi-production processes, applying, respectively, the IA method and the VMW method. In this paper we examine the relation between the scattering amplitude T and the production amplitude F from the viewpoint of the unitarity and the final state interaction (FSI) theorem by using a simple field theoretical model. As a result it is shown that the amplitudes in the physical state representation are directly represented through the Breit-Wigner amplitudes of the relevant resonances, and the respective forms of T and F coincide with those in the IA and VMW methods, justifying our methods of analyses.

hep-ph↗
arXiv1998

Reply to the criticism raised by Pennington on our pipi-Production Amplitudes

A recent criticism raised by M.R.Pennington on our pipi-production amplitudes seems to be due to his misunderstanding on our description, and is not right. Essential point of the relation between our scattering and production amplitudes is, in connection to the unitarity and the final state interaction theorem, briefly explained.

hep-ph↗
arXiv1997

Existence of σ(600)/κ(900)-Particle and New Chiral Scalar Nonet ``Chiralons''

The σ(600) and κ(900), observed in the phase shift analyses, satisfy rather well the mass and width relation predicted by the SU(3)LsM and the SU(3)LsM with the vector and axial-vector meson nonets, and deserve to be the members of scalar σ-nonet, together with the observed resonances a_0(980) and f_0(980), as a chiral partner of pseudoscalar π-nonet. In the phase shift analyses an introduction of repulsive background phase δ_{BG} is essential, whose origin has a close connection to the λϕ^4 interaction in LsM. It is argued that the members of this σ-nonet, "Chiralons", have different properties and should be discriminated from the conventional ^3P_0-qqbar-scalar nonet.

hep-ph↗
arXiv1997

Re-analysis of ππ/ KπPhase Shift and Existence of σ$(600) / κ(900)-Particle

Re-analyzing the old phase shift data of I=0, ππ(I=1/2, Kπ) scattering, we show an evidence for existence of the σ-particle (κ-particle) with a comparatively light mass, which has been missing for a long time: In the analysis we have applied a new method of interfering Breit-Wigner amplitudes, which makes the scattering amplitude parametrized in terms of only physical quantities, mass and width of resonant particles, in conformity with unitarity. We have introduced phenomenologically a background phase shift δ_{BG} of repulsive core type. The χ^2-fits of the both ππ- and Kπ- phase shifts are improved greatly with the δ_{BG} over the conventional fits without it.

hep-ph↗
arXiv1997

σ-Particle in Production Processes

A S-wave ππresonance below 1 GeV/c^2, sigma has been observed in analyses of the phase shift data of ππscatterings. It is important to observe it in production processes. A huge events of π^0π^0 below 1 GeV/c^2 is seen in the central production of the GAMS experiment. Its mass spectrum is well described by the variant mass and width method (VMW) including f_0(980), f_2(1270) and a S-wave resonance which might be assigned to be a sigma. We report here that the angular distributions of the π^0π^0 system are also described with the S-wave resonance interfering with f_0(980) and the tail of f_2(1270) by VMW. The same method is applied to the π^+π^- data of J/ψ\to ωππdecay, and is shown that not only π^+π^- mass spectrum but also its cosθ_πdistributions are described well.

hep-ph↗
arXiv1997

Relation between Scattering and Production Amplitude - Case of Intermediate σ-Particle in ππ-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 σ-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 ππ-scattering amplitude are powerless for this purpose.

hep-ph↗
arXiv1997

On existence of the σ(600) - Its physical implications and related problems

We make a re-analysis of I=0 ππscattering phase shift δ_0^0 through a new method of S-matrix parametrization (IA; interfering amplitude method), and show a result suggesting strongly for the existence of σ-particle -- long-sought Chiral partner of π-meson. Furthermore, through the phenomenological analyses of typical production processes of the 2π-system, the pp-central collision and the J/Ψ\to ωππdecay, by applying an intuitive formula as sum of Breit-Wigner amplitudes, (VMW; variant mass and width method), the other evidences for the σ-existence are given. The validity of the methods used in the above analyses is investigated, using a simple field theoretical model, from the general viewpoint of unitarity and the applicability of final state interaction(FSI-) theorem, especially in relation to the ``universality'' argument. It is shown that the IA and VMW are obtained as the physical state representations of scattering and production amplitudes, respectively. The VMW is shown to be an effective method to obtain the resonance properties from production processes, which generally have the unknown strong-phases. The conventional analyses based on the ``universality'' seem to be powerless for this purpose.

hep-ph↗
arXiv1997

Further Analysis on σ-particle Properties

In a previous work, we have reanalyzed the I=0 S-wave ππ-scattering phase-shift through a new method of Interfering Breit-Wigner amplitudes, and have shown the existence of a light scalar, σparticle, accompanied by a negative "repulsive core"-type background phase-shift, whose origin may have some correspondence to a ``compensating'' ππcontact interaction. In this work we make further analysis on the phase shift under KKbar threshold from the same standpoint, to determine precise values of σmass and width, so far as present experimental data are concerned.

hep-ph↗
arXiv1997

Analysis of Kπ-scattering phase shift and existence of κ(900)-particle

Recently we have shown an evidence for existence of σ-particle in the previous works; where the ππS-wave phase shift is reanalyzed, by introducing a repulsive background suggested by the chiral symmetry, and by applying a new method of Interfering Breit-Wigner Amplitudes. In this work we also show, reanalyzing the KπS-wave phase shift from a similar standpoint, an evidence for existence of κ(900), possibly to be a member of σ-nonet.

hep-ph↗
arXiv1997

Spectra of Exclusive Semi-Leptonic Decays of B-meson in the Covariant Oscillator Quark Model

The spectra and form factors of exclusive semi-leptonic decays of B-meson are analyzed, taking account of confined effects of quarks by the Covariant Oscillator Quark Model. The predicted B --> (D*,D)l nubar_l spectra with the conventional value of V_cb are fit well to the high-precision experiment. It is also shown the values of V_cb and V_ub obtained through decay widths for the B --> (D,D*,rho)l nubar_l processes are consistent with the presently accepted ones.

hep-ph↗