Experimental Determination ofReξfromKμ30Decay

From measurements of the polarization of muons from $K_{\mu 3}^{}{}_{}{}^0$ decay, we have found the average longitudinal component to be 0.88 ± 0.25, and the average component in the plane of decay but perpendicular to the muon momentum to be 0.369 ± 0.036. From these we determined $\mathrm{Re}\xi =-{1.75}_{-0.2\mathrm{}}^{+0.5\mathrm{}}$, assuming constant form factors. The behavior of $\mathrm{Re}\xi \mathrm{}\left(0\right)\mathrm{}$ with varying form factors is discussed.