# First measurement of the CP-violating phase in $B_s^0 \to \phi \phi$ decays

Abellan, Beteta C, Adeva, B, Adinolfi, M, Adrover, C, Affolder, A, Ajaltouni, Z, Albrecht, J, Alessio, F, Alexander, M, Ali, S
et al (show 120 more authors) (2018) First measurement of the CP-violating phase in $B_s^0 \to \phi \phi$ decays. The Journal of High Energy Physics, 2018 (3).

A flavour-tagged time-dependent angular analysis of $B^0_s\to J/\psi\phi$ decays is presented where the $J/\psi$ meson is reconstructed through its decay to an $e^+e^-$ pair. The analysis uses a sample of $pp$ collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb$^{-1}$. The $CP$-violating phase and lifetime parameters of the $B^0_s$ system are measured to be $\phi_s=0.00\pm0.28\pm0.07$ rad, $\Delta\Gamma_s=0.115\pm0.045\pm0.011$ ps$^{-1}$ and $\Gamma_s=0.608\pm0.018\pm0.012$ ps$^{-1}$ where the first uncertainty is statistical and the second systematic. This is the first time that $CP$-violating parameters are measured in the $B^0_s\to J/\psi\phi$ decay with an $e^+e^-$ pair in the final state. The results are consistent with previous measurements in other channels and with the Standard Model predictions.