New Limit for Isotopic Spin Conservation in Strong Interactions from an Experimental Limit onσ(d+d→He4+π0)

The strong reaction $d+d\to {\mathrm{He}}^4+{\pi }^0$, which is forbidden by isotopic spin conservation, has been looked for with a 460-MeV deuteron beam from the Berkeley 184-in. cyclotron. Preliminary results were reported elsewhere. A more comprehensive analysis of this same experiment has recently been completed. From this analysis, an upper limit for the differential cross section for the reaction in the c.m. system at about ${\Theta }_{\mathrm{c}.\mathrm{m}.\mathrm{}}=90\mathrm{}$ deg is found to be (0.097±0.027)×${10}^{-33\mathrm{}}$ ${\mathrm{cm}}^2$/sr. The data are consistent with no ${\pi }^0$ production. From a comparison of this upper limit with the theoretical prediction of the cross section for this reaction if isotopic spin need not be conserved, we conclude that isotopic spin is at least (99.74±0.08)% conserved in this strong interaction.