Measurement of CP violation in the $B_s^0rightarrowphiphi$ decay and search for the $B^0rightarrow phiphi$ decay

A measurement of the time-dependent CP-violating asymmetry in $B_s^0rightarrowphiphi$ decays is presented. Using a sample of proton-proton collision data corresponding to an integrated luminosity of $5.0$fb$^{-1}$ collected by the $mbox{LHCb}$ experiment at centre-of-mass energies $sqrt{s} = 7$ TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 $B_s^0rightarrowphiphi$ decays is obtained. The CP-violating phase $phi_s^{sbar{s}s}$ is measured to be $-0.073 pm 0.115$(stat)$pm 0.027$(syst) rad, under the assumption it is independent on the helicity of the $phiphi$ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be $|lambda|=0.99 pm 0.05 $(stat)$ pm 0.01 $(syst). In addition, $T$-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in $brightarrowbar{s}sbar{s}$ transitions. Finally, a limit on the branching fraction of the $B^0rightarrow phiphi$ decay is determined to be $mathcal{B}(B^0rightarrow phiphi)<2.7times 10^{-8}$ at 90% confidence level.