Evidence for $B^0\to\rho^0\rho^0$ decays

We present the results of a search for $B^0\rightarrow\rho^0\rho^0$ decays. The analysis is based on a sample of 384 million $B\bar{B}$ pairs recorded with the BaBar detector. We extract $100^{+32}_{-31}\pm 17$ $\rho^0\rho^0$ events, corresponding to a branching fraction of $(1.07^{+0.34+0.19}_{-0.32-0.18})\times 10^{-6}$, and a fraction of longitudinally polarized events of $0.87^{+0.12}_{-0.13}\pm 0.04$. The significance of the signal is 3.5$\sigma$ including systematics. We estimate the systematic uncertainty on the CKM unitarity angle $\alpha$, due to penguin contributions, to be $18^{\circ}$ at the 1$\sigma$ level.