MASS AND WIDTH OF THE SIGMA(750) SCALAR MESON FROM MEASUREMENTS OF PI-N-]PI(-)PI-N+ ON POLARIZED TARGETS

The measurements of reactions pi(-)p(up arrow)-->pi(-)pi(+)n at 17.2 G eV/c and pi(+)n(up arrow)-->pi(+)pi(-)p at 5.98 and 11.85 GeV/c on pol arized targets at CERN provide model-independent and solution-independ ent evidence for a narrow scalar state sigma(750). The original chi(2) minimization method and the recent Monte Carlo method for the amplitu de analysis of data at 17.2 GeV/c are in excellent agreement. Both met hods find that the mass distribution of the measured amplitude \(S) ov er bar\(2) Sigma with recoil transversity ''up'' resonates near 750 Me V while the amplitude \S\(2) Sigma with recoil transversity ''down'' i s large and nonresonating. The amplitude \S\(2) Sigma contributes as a strong background to S-wave intensity I-s=(\S\(2)+\(S) over bar\(2))S igma and distorts the determinations of sigma resonance parameters fro m I-s. To avoid this problem we perform a series of Breit-Wigner fits directly to the measured distribution \(S) over bar\(2) Sigma. The inc lusion of various backgrounds causes the width of sigma(750) to become very narrow. Our best fit with a t-averaged coherent background yield s m(sigma)=753 +/- 19 MeV and Gamma(sigma)=108 +/- 53 MeV. These value s are in excellent agreement with the Ellis-Lanik theorem for the widt h of scalar gluonium. The gluonium interpretation of sigma(750) is als o supported by the absence of sigma(750) in reactions gamma gamma-->pi pi. We also show how data on polarized target invalidate essential as sumptions of past determinations of pi pi phase shifts which explains the absence of sigma(750) in the conventional phase shift delta(0)(0). We examine the interference of sigma(750) with f(0)(980) and find it has only st very small effect on the determination of the sigma(750) m ass and width. The data on the amplitude \(S) over bar\(2) Sigma in th e mass range of 1120-1520 MeV show the existence of a scalar resonance f(0)(1300) with a mass of 1280 +/- 12 MeV and a width of 192 +/- 26 M eV. Our results emphasize the need for a systematic study of productio n processes on the level of spin amplitudes measured in experiments wi th polarized targets.