$\alpha $ PARAMETER FOR ${{\boldsymbol \eta}}$ $\rightarrow$ 3 ${{\boldsymbol \pi}^{0}}$
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See the ``Note on ${{\mathit \eta}}$ Decay Parameters'' in our 1994 edition, Phys.Rev.$\mathbf {D50}$, 1 August 1994, Part$~$I, p.$~$1454. The value here is of $\alpha $ in $\vert $matrix element$\vert ^2$ = 1 + 2${}\alpha {}\mathit z$.