Study of the $B_s^0\rightarrow\phi\phi$ Decay and Measurement of its Branching Ratio with CDF

We present a measurement of the $B_s^0\rightarrow\phi\phi$ branching ratio using approximately 2.9~fb$^{-1}$ of data collected with the CDF\,II detector at the Fermilab Tevatron. The first measurement of this decay mode was performed at CDF in 2005 using a 180~pb$^{-1}$ data sample where eight signal events were seen. We select events in the displaced track trigger sample and optimize the event selection requirements. The procedure to optimize the selection and estimates of the expected background are described. The preliminary result for the branching ratio is in agreement with theoretical predictions and the previous analysis. It is now dominated by the experimental uncertainty in the $B_s^0 \rightarrow J/\psi \phi$ branching ratio which is used for normalization.