First measurement of the CP-violating phase inB${}_s^0$ → J/$\psi$(→$e^{+}{e}^{-}$)$\varphi$ decays

A flavour-tagged time-dependent angular analysis of B${}_s^0$ → J/$\psi \varphi$ 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${}_s^0$ system are measured to be ${\varphi }_s$ = 0.00±0.28±0.07 rad, $\Delta {\Gamma }_s$ = 0.115±0.045±0.011 ps${}^{-1}$ and ${\Gamma }_s$ = 0.608±0.018±0.012 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${}_s^0$ → J/$\psi \varphi$ 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.