Prospects for B degrees(s) ? p degrees p degrees and B degrees(s) ? ?? modes and corresponding CP asymmetries at Tera-Z

The physics potential of measuring B0(3) -r0r0 and B0(3) -eta eta decays via four-photon final states at Tera-Z phase of CEPC or FCC-ee is investigated in this paper. We propose an electromagnetic calorimeter (ECAL) with both high energy resolution and excellent separation power to efficiently reconstruct r0 and eta from hadronic final states with high photon multiplicity. The resulting B-meson mass resolution is approximately 30 MeV, allowing 3 sigma separation between B0 and B30. With the assistance of the b-jet tagging, the relative sensitivities to B0- r0r0, B30 -r0r0, B0 -eta eta, and B30 -eta eta signal strengths at Tera-Z are projected as 0.45%, 4.5%, 18%, and 0.95%, respectively. Their dependence on various detector performances is also discussed. In addition, B0 -r0r0 and its two isospin-related modes are paid special attention due to their roles in the determination of the CKM angle alpha (phi 2). The anticipated precisions of their branching-ratio and CP- asymmetry measurements at Tera-Z are evaluated. We show that the measurement of the time-integrated B0 -r0r0 CP asymmetry at Tera-Z is complementary to B-factory ones. The precision on alpha combining Z- and B-factory results reaches0.4?, lower than the systematic uncertainties attached to isospin breaking.