2π0Mass Spectrum and Determination of the Spin of thef0Usingπ−+p→π0+π0+nat 10 BeV/c*

The properties of the ${\pi }^0-{\pi }^0$ system have been studied using the interaction ${\pi }^{-}+p\to {\pi }^0+{\pi }^0+n$ at 10 BeV/c, by observing only the four gammas produced. The ${\pi }^0{\pi }^0$ mass spectrum shows a strong $f^0$ peak centered at 1275±25 MeV. A broad second enhancement, extending from threshold to Å800 MeV, cannot be interpreted definitively because of a large beckground (only in this mass region) of gammas from $3{\pi }^0$ events. The $f^0$ differential production cross section falls off initially as $e^{\mathrm{At}}$ where $A\approx 10$. For small four-momentum transfer events ($t\le 5m_{\pi }^{}{}_{}{}^2$), the $\pi \pi$ scattering distribution in the $f^0$ rest frame agrees well with ${\left[P_2\right(cos{\theta }_{\pi \pi }\left)\right]}^2$, where $P_2$ is the second Legendre polynomial. This indicates that the simplest one-pion-exchange model is applicable under these conditions, and allows us to conclude that the $f^0$ spin is 2, not 0 or 4. The $f^0$ production cross section times its branching ratio for $2{\pi }^0$ decay is 20±5 μb. The $g^0$ meson ($2\pi$ resonance at 1670 MeV) is not observed and an upper limit of 5 μb is set for its production cross section times its branching ratio into $2{\pi }^0\text{'}\mathrm{s}$.