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.

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