Possible Determination of the Spin of theΞ−from the Angular Asymmetry of Its Decay

The ${\Xi }^{-}$ hyperon is produced in a parity-conserving interaction involving only a proton and two spinless $K$ mesons. Therefore, the ${\Xi }^{-}$ beam in any direction consists of an equal, incoherent mixture of two pure spin states which go into each other under 180° rotation in the production plane. This condition implies a new restriction upon the angular distribution of the ${\Xi }^{-}$ decay products. In particular, the distribution $I(\theta ,\phi )=1+Acos\theta$ is impossible for $A\ne 0$ unless the ${\Xi }^{-}$ spin is ½.