Measurement of the CP-violating phase ${\varphi }_s$ in ${\bar{B}}_s^0\to J\mathrm{/}\psi {\pi }^{+}{\pi }^{-}$ decays

The mixing-induced CP-violating phase ${\varphi }_s$ in $B_s^0$ and ${\bar{B}}_s^0$ decays is measured using the $J\mathrm{/}\psi {\pi }^{+}{\pi }^{-}$ final state in data, taken from 3,fb${}^{-1}$ of integrated luminosity, collected with the LHCb detector in 7 and 8 TeV centre-of-mass $pp$ collisions at the LHC. A time-dependent flavour-tagged amplitude analysis, allowing for direct \CP violation, yields a value for the phase ${\varphi }_s=70\pm 68\pm 8$,mrad. This result is consistent with the Standard Model expectation and previous measurements.