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Tomohito Maeda

Publications and source records attributed to Tomohito Maeda.

15 recordsLinked to original sources
arXiv2019

Radiative decays of light-quark mesons to a pion revisited in the covariant oscillator quark model

The present talk consists of two parts. The first one is allocated for consideration of the dimension of bilocal meson fields for quark-antiquark meson systems, which have been so far treated as the bosonic fields independent of constituent quark flavors, in the covariant oscillator quark model. Revisiting the electromagnetic currents of quark-antiquark meson systems, we show that the bilocal meson fields should be bosonic for light-quark meson systems, while fermionic for heavy-light and heavy-heavy meson systems. In the second part we apply the effective electromagnetic interactions of meson systems derived in the first part to radiative decay processes for the excited states of light-quark mesons. The calculated results for the $πγ$ decay widths of the $a_1(1260)$, $a_2(1320)$, $b_1(1235)$ and $π_2(1670)$ mesons are in fair agreement with experiment, except for the $b_1(1235)$ meson. As for the $ρ(770)^0 γ$ decay width of the $f_1(1285)$ the present model strongly supports the experimental results in 1995 and 2016, respectively, of VES and CLAS Collaborations, not the average value by the Particle Data Group.

hep-ph↗
arXiv2018

Proper-time Quantum Mechanics for Multi-Quark System and Composite-Hadron Spectroscopy

One of the most important problem in hadron physics is to establish the Lorentz-invariant classification scheme of composite hadrons, extending the framework of non-relativistic quark model. We present an attempt, by developing proper-time $τ$ quantum mechanics on a multi-quark system in particle frame (with constant boost velocity $\boldsymbol{v}$). We start from the variational method on a classical mechanics action where a constituent quark has Pauli-type $SU(2)_σ$ spin. Then the $SU(2)_{\mathfrak{m}}$ symmetry, concerning the sign-reversal on quark mass, has arisen with the basic vectors, the normal Dirac spinor with $J^{P}=(1/2)^{+}$ and the chiral one with $J^{P}=(1/2)^{-}$, appearing as a "shadow" of the former. Herewith, the mass reversal between these basic vectors become equivalent to the chirality, which is a symmetry of the standard gauge theory. We describe the role of chirality in hadron spectroscopy and regard it as attribute {$χ$} of "elementary" hadrons in addition to {$J, P, C$}. A novel feature of our hadron spectroscopy is, in the example of $q\bar{q}$ meson system, that the "Regge trajectories", are given by mass-squared vs. the number of quantum $N$ ; where $M^2 =M_{0}^2 +2NΩ$ ($N=2n$, $n$ the radial quantum number, $Ω$ the oscillator quantum), and the intrinsic spin of hadrons $\boldsymbol{J}$ comes only from quark spin $\boldsymbol{S}$, $\boldsymbol{J}=\boldsymbol{S}$. Some phenomenological facts crucial to its validity are pointed out on the light-through-heavy quarkonium system.

hep-ph↗
arXiv2013

Radiative pi^pm gamma transitions of excited light-quark mesons in the covariant oscillator quark model

The COMPASS collaboration, as a part of their hadron spectroscopy program, is going to measure the radiative decay widths of light-quark mesons via the Primakoff reactions. In this letter we study the photon couplings of light-quark q qbar states in the covariant oscillator quark model and evaluate the transition rates for {rho(770), b_1(1235), a_1(1260), a_2(1320), pi_2(1670), rho_3(1690), rho(1700)}^pm to pi^pm gamma, which are expected to be measured by the COMPASS. Such photon couplings could be useful not only for understanding the internal structures of observed light-quark mesons and their quark-model classification but also for the ongoing experimental studies by COMPASS.

hep-ph↗
arXiv2010

D_{s1}^{*}(2710) and D_{sJ}^{*}(2860) in the U~(12)*O(3,1)-scheme

In order to classify the charmed-strange mesons, including puzzling D_{s0}^{*}(2317) and D_{s1}(2460), and recently observed D_{s1}^{*}(2710) and D_{sJ}^{*}(2860), we employ the U~(12)*O(3,1) level-classification scheme of hadrons proposed and developed by us in recent years. The scheme has a new degree of freedom, SU(2)_ρ, which leads to a number of extra states out of conventional SU(6)-scheme, named chiralons. Applying this novel classification scheme, we investigate the strong decays of S- and P-wave c\bar{s} mesons with one pseudoscalar emission by using the covariant oscillator quark model. As a result it is shown that D_{s0}^{*}(2317) and D_{s1}(2460) are described as {}^{1}S_{0}^χ and {}^{3}S_{1}^χ chiralons, forming the SU(2)_ρ doublet with the ground-state D_{s}^{} and D_{s}^{*}, respectively. Furthermore, the observed decay properties of D_{s1}^{*}(2710) is consistently explained as the vector chiralon {}^{1}P_{1}^χ. On the other hand, it is also found that the controversial narrow state, D_{sJ}^{*}(2860), does not fit as predicted properties of our P-wave vector chiralon.

hep-ph↗
arXiv2008

The qqbar S-wave axial-vector mesons in the covariant U~(12)-scheme

We study the properties of axial vector mesons a1 and b1 as relativistic S-wave states which are predicted in the U~(12)-scheme, through the analyses of their radiative and pionic decays. Specifically, partial widths of the strong a1 (b1) -> rho(omega) pi processes, their D/S-wave amplitude ratios, and radiative transition widths of a1(b1) -> pi gamma processes are calculated by using a simple decay interaction model, and made a comparison with the respective experimental values.

hep-ph↗
arXiv2006

Radiative Decays of q bar q Chiral States in the U~(12)-Scheme

The radiative transitions between ground-states (GS) of light q bar q mesons are investigated in the U~(12)-scheme. In this scheme the rich decay-spectra are offered even in transition between GS due to the appearance of chiral states. As a result the radiative decay widths of the ordinary V -> P gamma process are well reproduced, and furthermore, the predicted width of b_{1}(1235) -> pi gamma process (Gamma_{theor}=229 keV), by assigning b_{1}(1235) as a member of the {}^{3}S_{1} chiral states A^{(E)}, is in good agreement with experimental one (Gamma_{exp} =230 +- 60 keV). From this results it is indicated that b_{1}(1235) meson, classified as {}^{1}P_{1} state in conventional non-relativistic (NR) classification scheme, is a good candidate of chiral state in the U~(12)-scheme. The other radiative transition widths of some chiral states are also predicted. Accordingly the predicted values given here, will provide useful insights in their search at BES.

hep-ph↗
arXiv2005

Four Quark cn - nbar cbar States in U(12)-Scheme and X(3872)/Y(3940)

The properties of four quark cn - nbar cbar states are investigated as cn di-quark and nbar cbar di-antiquark system in U(12)-classification scheme of hadrons, recently proposed by us. We consider the negative-parity di-quark and di-antiquark in ground states, which form with the ordinary positive-parity ones the respective linear representations of chiral symmetry. The masses and widths of ground-states are predicted by using Joint Spring Quark Model, and the observed properties of X(3872) and Y(3940) are consistent, respectively, with those of the JPC=1++ and 2++ states from the negative-parity di-quark and di-antiquark. Their narrow-widths are explained from an orthogonality of spinor wave functions. The properties of ground-state cs - sbar cbar system are also predicted in this scheme.

hep-ph↗
arXiv2005

Chiral Mass Splitting for c \bar{s} and c \bar{n} Mesons in the \tilde{U}(12)-Classification Scheme of Hadrons

We investigate the chiral mass splitting of parity-doubled J=0,1 states for c \bar{s} and c \bar{n} meson systems in the \tilde{U}(12)_{SF}-classification scheme of hadrons, using the linear sigma model to describe the light-quark pseudoscalar and scalar mesons together with the spontaneous breaking of chiral symmetry, and consequently predict the masses of as-yet-unobserved (0^{+},1^{+}) c \bar{n} mesons. We also mention some indications of their existence in the recent published data from the Belle and BABAR Collaborations.

hep-ph↗
arXiv2005

The DsJ*(2317) and DsJ(2460) mesons in U~(12)-classification scheme of hadrons

The narrow mesons, DsJ*(2317) and DsJ(2460), observed recently in the final states Ds+ pi0 and Ds*+ pi0 are pointed out to be naturally assigned as the ground-state scalar and axial-vector chiral states in the csbar system, which would newly appear in the covariant U~(12) hadron-classification scheme proposed a few years ago. We predict the comparatively large electromagnetic decay widths to other models, which are due to the intrinsic electric dipole moment. The SELEX state DsJ(2632) is also able to be assigned to the P-wave chiral state with JP=1- in the U~(12)-classification scheme.

hep-ph↗
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↗
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

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

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.

hep-ph↗