$CP$ Invariance Study of $J/psitoLambdabarLambda$ and $Lambda$ Nonpleptonic Decays in Helicity Frame

We present the joint helicity amplitudes for $J/psi to Lambda bar{Lambda}$, $Lambda(barLambda)$ decays to different final states in the helicity frame. Two observables to search for $CP$ violation in $J/psitoLambdabarLambda$ can be expressed with the information of helicity angles of baryon and antibaryon. Four decay parameters of $Lambda$ and $barLambda$, namely, $alpha_-,alpha_+,alpha_0$ and $baralpha_0$, can be obtained with the joint helicity amplitude equations by the likelihood fit method. With the data sample of $10^{10}$ $J/psi$ decays accumulated by BESIII, the precision of the measurements is estimated to be about $10^{-3}$.