Search for the decay $B^0\to \phi \phi$

A search for the decay $B^0\to \phi \phi$ is made using $pp$ collision data collected with the LHCb detector at centre-of-mass energies of 7, 8 and 13 TeV, corresponding to an integrated luminosity of $9$ fb${}^{-1}$. No significant signal is observed, and an upper limit on the branching fraction of $1.3(1.4)\times {10}^{-8}$ at $90(95)\mathrm{\%}$ confidence level is set. This result supersedes the previous LHCb study and improves the upper limit by a factor of two.