Improving the measurement of the CKM phase $phi_2 = alpha$ in $B to pi pi$ and $B to rho rho$ decays

CP-violating asymmetries in $B to pi pi$ and $B to rho rho$ decays can help specify the weak phase $phi_2 = alpha$ of the Cabibbo-Kobayashi-% Maskawa (CKM) matrix. We discuss the impact of improved measurements of these processes such as will be available in the near future, finding special value in better measurement of the time-dependent CP violation parameter $S_{00}$ in $B^0 to pi^0 pi^0$ and $B^0 to rho^0 rho^0$. Reducing the errors on $B to rho rho$ measurements by a factor of two can potentially lead to an error in $phi_2 = alpha$ just above $2^circ$, at which level isospin-breaking corrections must be considered.