arXiv subjects
Publications and source records attributed to Tsuneaki Tsuru.
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.
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.
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.
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.
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.
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.
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.
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.