Test of time-reversal invariance in the beta decay ofCo56

A limit on time reversal noninvariance is obtained by measuring the $\beta -\gamma$ angular correlation in the decay of oriented ${}_{}{}^{56}{}_{}{}^{}\mathrm{Co}$. From a search for a correlation of the form $E_1\left(\hat{J}·\hat{k}\right)(\hat{J}·\hat{p}\times \hat{k})$, where $\hat{J}$, $\hat{p}$, and $\hat{k}$ are unit vectors in the direction of the orientation axis, positron momentum, and photon momentum, respectively, we obtain $E_1=\frac{2ysin\phi }{(1+v^2)}=-0.011\mathrm{}\pm 0.022$, where $y{e}^{i\phi }=\frac{C_{\mathrm{V}}{M}_{\mathrm{F}}}{C_{\mathrm{A}}{M}_{\mathrm{GT}}}$.