The σ-meson production in excited ϒ decay processes: constraint from chiral symmetry

We analyze the ππ production amplitudes in the excited Υ decay processes, Υ (2S) → Υ (1S)π + π − , Υ (3S) → Υ (1S)π + π − and Υ (3S) → Υ (2S)π + π − , and the ππ and KK production amplitudes in the charmonium decay processes, ψ(2S) → J/ψπ + π − and J/ψ → φπ + π − , φK + K − , including the possible effect of light σ production. The amplitudes are parametrized by the sum of Breit-Wigner amplitudes for the σ and the other relevant particles and of the direct 2π-production amplitude, following the VMW method. All the ππ (and KK) mass spectra are reproduced well with the obtained values of σ-parameters, mσ = 526 +48 −37 MeV and Γσ = 301 +145 −100 MeV, which is almost consistent with the values in our previous phase shift analyses. §1. IntroductionWhether the light σ-meson really exists or does not is an important problem in hadron physics. For many years, its existence had been neglected phenomenologically mainly due to the negative result of the analyses of I = 0 S-wave ππ scattering phase shift.In many ππ-production experiments, a large event concentration or a bump structure in the spectra of ππ invariant mass m ππ around 500 MeV had been observed, however, conventionally it was not regarded as σ-resonance, but as a mere ππ-background, under influence of the so callled "universality argument." 1) In this argument, it is stated that because of the unitarity of S-matrix and of the analyticity of the amplitudes, the ππ production amplitude F takes the form F = α(s)T (T being the ππ scattering amplitude), with a slowly varying real function α(s). The pole position of S-matrix is determined solely through the analysis of T , which was believed to have no light σ-pole at that time.Recently the data of ππ-scattering phase shift had been reanalyzed by many groups 2) including ours and the existence of light σ(450 ∼ 600) was strongly suggested. The result of no σ-existence in the conventional analyses was pointed out 3) to be due to the lack of consideration on the cancellation mechanism guaranteed by chiral symmetry, and shown to be not correct. Furthermore, we have pointed out that the "universality argument" should be revised, taking into account the quark physical picture of hadrons 4) : The essential point is that the strong interaction is a residual interaction of QCD among all color-neutral bound states of quarks, anti-

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“…The consistency of our result of analyses with the general constraints from chiral symmetry is discussed in the separate talk 10) .…”

Section: Results and Conclusionsupporting

confidence: 67%

The σ-Meson Production in Excited ϒ Decay Processes

Komada

Ishida

2002

AIP Conference Proceedings

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“…In addition, by the end of the nineties and throughout the first decade of the new millennium, virtually all approaches that fitted either heavy meson decays and/or ππ scattering phases containing at the very least some minimal implementation of chiral symmetry, unitarity and analyticity obtained a pole around 430 to 550 MeV corresponding to a broad resonance whose width lied between 400 to 600 MeV (for references on these years see [74,75,76,96,98,99,100,101,102,103,104]). This can be checked in Fig.4. …”

Section: Poles From Unitarity and Chiral Perturbation Theorymentioning

confidence: 99%

“…By analyzing ππ [98] and Kπ [322] scattering data they found that σ and κ poles where necessary. In these works an ad hoc deformation of the Breit-Wigner formalism was used.…”

Section: Extended and Unitarized Lσmmentioning

confidence: 99%

From controversy to precision on the sigma meson: A review on the status of the non-ordinary f0(500) resonance

2016

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The existence and properties of the sigma meson have been controversial for almost six decades, despite playing a central role in the spontaneous chiral symmetry of QCD or in the nucleonnucleon attraction. This controversy has also been fed by the strong indications that it is not an ordinary quark-antiquark meson. Here we review both the recent and old experimental data and the model independent dispersive formalisms which have provided precise determinations of its mass and width, finally settling the controversy and leading to its new name: f 0 (500). We then provide a rather conservative average of the most recent and advanced dispersive determinations of its pole position √ s σ = 449 +22−16 −i(275±12). In addition, after comprehensive introductions, we will review within the modern perspective of effective theories and dispersion theory, its relation to chiral symmetry, unitarization techniques, its quark mass dependence, popular models, as well as the recent strong evidence, obtained from the QCD 1/N c expansion or Regge theory, for its non ordinary nature in terms of quarks and gluons.

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“…However, the immediate conceptual problem arises, since, whatever this meson is called, the strength of the two pion distribution does not follow the shape provided by the exchange of such a heavy and broad meson. The isoscalar two pion distribution at low energies is governed by the scattering matrix of two pions in L=0, I=0, which has a broad bump consisting of a large background on top of the effects of the σ pole, which is now present in all modern theoretical [23,24,25] and experimental analyses [26,27], (see also the proceedings of the σ Workshop [28] ). The pole of the σ appears in all these approaches with a mass around 500 MeV and a width around 400 MeV, and, as mentioned above, there is also a large background present in the ππ t-matrix.…”

Section: Introductionmentioning

confidence: 99%

Two pion decay of the Roper resonance

2002

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We evaluate the two pion decay of the Roper resonance in a model where explicit re-scattering of the two final pions is accounted for by the use of unitarized chiral perturbation theory. Our model does not include an explicit ǫ or σ scalar-isoscalar meson decay mode, instead it generates it dynamically by means of the pion re-scattering. The two ways, explicit or dynamically generated, of introducing this decay channel have very different amplitudes. Nevertheless, through interference with the other terms of the model we are able to reproduce the same phenomenology as models with explicit consideration of the ǫ meson.

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The σ-meson production in excited ϒ decay processes: constraint from chiral symmetry

Cited by 30 publications

References 26 publications

The σ-Meson Production in Excited ϒ Decay Processes

The σ-Meson Production in Excited ϒ Decay Processes

From controversy to precision on the sigma meson: A review on the status of the non-ordinary f0(500) resonance

Two pion decay of the Roper resonance

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