The paper "Measurement of the branching fraction, polarization and time-dependent \(CP\) asymmetry in \(B^0 \to \rho^+\rho^-\) decays and constraint on the CKM angle \(\phi_2\)" in which Ryogo Okubo has contributed as the main author, was published in Physical Review D.

This paper reports measurements of the branching fraction, the polarization, and the matter-antimatter asymmetry (CP asymmetry) of the decay time distributions of the \(B^0\to \rho^+\rho^-\) decays. The results of these measurements are used to determine the parameter of the unitary triangle in the Kobayashi-Maskawa theory, which is crucial for constraining the effects of physics beyond the Standard Model in the \(B^0-\bar{B}^0\) mixing. Our isospin analysis of the \(B\to\rho\rho\) system, using the results of this study, improves the precision of \(\phi_2 (\alpha)\), which is one of the parameters of the unitary triangle, by \(10\ \%\) relative to the world average.

Paper information:
I. Adachi et al., "Measurement of the branching fraction, polarization and time-dependent \(CP\) asymmetry in \(B^0 \to \rho^+\rho^-\) decays and constraint on the CKM angle \(\phi_2\)"
[Phys. Rev. D, 111, 092001, 2025. https://doi.org/10.1103/PhysRevD.111.092001]