  The measurement of $\sin 2 \beta$ is discussed within and beyond the standard
model. In the presence of new physics, the angle $\beta$ extracted from the
global fit(denoted by $\beta^{SM}_{fit}$) and the one extracted from $B\to
J/\psi K_S$ (denoted by $\beta_{J/\psi}$) are in general all different from the
'true' angle $\beta$ which is the weak phase of CKM matrix element $V^*_{td}$.
Possible new physics effects on the ratio $R_{\beta}=\sin2\beta_{J/\psi}/\sin
2\beta^{SM}_{fit}$ is studied and parameterized in a most general form. It is
shown that the ratio $R_{\beta}$ may provide a useful tool in probing new
physics. The experimental value of $R_{\beta}$ is obtained through an update of
the global fit of the unitarity triangle with the latest data and found to be
less than unity at 1$\sigma$ level. The new physics effects on $R_{\beta}$ from
the models with minimum flavor violation (MFV) and the standard model with
two-Higgs-doublet (S2HDM) are studied in detail. It is found that the MFV
models seem to give a relative large value $R_{\beta}\geq 1$. With the current
data, this may indicate that this kind of new physics may be disfavored and
alternative new physics with additional phases appears more relevant. As an
illustration for models with additional phase beyond CKM phase, the S2HDM
effects on $R_{\beta}$ are studied and found to be easily coincide with the
data due to the flavor changing neutral Higgs interaction.
