29 research outputs found
Further Analysis on \sigma-particle Properties
In a previous work, we have reanalyzed the I=0 S-wave \pi\pi-scattering
phase-shift through a new method of Interfering Breit-Wigner amplitudes, and
have shown the existence of a light scalar, \sigma particle, accompanied by a
negative "repulsive core"-type background phase-shift, whose origin may have
some correspondence to a ``compensating'' \pi\pi contact interaction. In this
work we make further analysis on the phase shift under KKbar threshold from the
same standpoint, to determine precise values of \sigma mass and width, so far
as present experimental data are concerned.Comment: Updated with recent progres
Re-analysis of \pi\pi / K\pi Phase Shift and Existence of \sigma$(600) / \kappa(900)-Particle
Re-analyzing the old phase shift data of I=0, \pi\pi (I=1/2, K\pi)
scattering, we show an evidence for existence of the \sigma-particle
(\kappa-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 \delta_{BG} of repulsive core type. The \chi^2-fits of the both
\pi\pi- and K\pi- phase shifts are improved greatly with the \delta_{BG} over
the conventional fits without it.Comment: Talk at HADRON'97, the 7th int. conf. on hadron spectroscopy, BNL,
August 1997. 4 pages with 3 eps figure
\sigma-Particle in Production Processes
A S-wave \pi\pi resonance below 1 GeV/c^2, sigma has been observed in
analyses of the phase shift data of \pi\pi scatterings. It is important to
observe it in production processes. A huge events of \pi^0\pi^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 \pi^0\pi^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 \pi^+\pi^- data of J/\psi
\to \omega\pi\pi decay, and is shown that not only \pi^+\pi^- mass spectrum but
also its cos\theta_\pi distributions are described well.Comment: Talk at HADRON'97, the 7th int. conf. on hadron spectroscopy, BNL,
August 1997. 4 pages with 2 eps figure
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.Comment: 8 pages, 1 Postscript figure, uses ptptex.st
Production of and from 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