Search for the Decay B0 --> ρ0 ρ0

The B0 --> ρ0ρ0 decay mode is searched for in a data sample of about 227 million Υ(4S) --> B(bar B) decays collected with the BABAR detector at the PEP-II asymmetric B factory at SLAC. No significant signal is observed, and an upper limit of 1.1x10-6 (90% C.L.) on the branching fraction is set. Implications on the penguin contribution and constraints on the CKM angle α with B --> ρρ decays are discussed. All results are preliminary