Search for W-exchange decays B0 -> Ds(*)- Ds(*)+

The authors report a search for the decays B0 → Ds-Ds+, B0 → D*s-Ds+ and B0 → D*s-D*s+ in a sample of 232 million Υ(4S) decays to B(bar B) pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+e- storage ring. They find no significant signal and set upper bounds for the branching fractions: Β(B0 → Ds-Ds+) < 1.0 x 10-4, Β(B0 → D*s- Ds+) < 1.3 x 10-4 and Β(B0 → D*s- D*s+) < 2.4 x 10-4 at 90% confidence level