$CP$ violation in $B_s^0$ decays at LHCb

Latest LHCb measurements of $CP$ violation in the interference between mixing and decay are presented based on $pp$ collision data collected during LHC Run I, corresponding to an integrated luminosity of $3.0, {rm fb}^{-1}$. Approximately $27, 000$ $B_s^0to J/psi pi^+pi^-$ signal events are used to make what is at the moment the most precise single measurement of the $CP$-violating phase in $bto cbar{c}s$ transitions, $phi_s^{cbar{c}s}=0.070pm0.068{rm (stat.)}pm0.008{rm (syst.)}$ rad. The most accurate measurement of the $CP$-violating phase in $bto sbar{s}s$ transitions, $phi_s^{sbar{s}s}$, is found from approximately $4, 000$ $B_s^0to phiphi$ signal events to be $phi_s^{sbar{s}s}=-0.17pm{rm (stat.)}0.15pm0.03{rm (syst.)}$ rad.

Measurement of CP violation in $B_s^0 to phi phi$ decays

A measurement of the decay time dependent CP-violating asymmetry in $B_s^0 to phiphi$ decays is presented, along with measurements of the $T$-odd triple-product asymmetries. In this decay channel, the CP-violating weak phase arises from the interference between $B_s^0$-$bar{B}_s^0$ mixing and the loop-induced decay amplitude. Using a sample of proton-proton collision data corresponding to an integrated luminosity of $3.0, fb^{-1}$ collected with the LHCb detector, a signal yield of approximately 4000 $B_s^0 to phiphi$ decays is obtained. The CP-violating phase is measured to be ${phi_s =-0.17pm0.15mathrm{,(stat)}pm0.03mathrm{,(syst)}}$ rad. The triple-product asymmetries are measured to be ${A_U=-0.003pm0.017mathrm{,(stat)}pm0.006mathrm{,(syst)}}$ and ${A_V=-0.017pm0.017mathrm{,(stat)}pm0.006mathrm{,(syst)}}$. Results are consistent with the hypothesis of CP conservation.

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

A first flavour-tagged measurement of the time-dependent CP-violating asymmetry in $B_s^0 to phiphi$ decays is presented. In this decay channel, the CP-violating weak phase arises due to CP violation in the interference between $B_s^0$-$bar{B}_s^0$ mixing and the $b to s bar{s} s $ gluonic penguin decay amplitude. Using a sample of $pp$ collision data corresponding to an integrated luminosity of $1.0; fb^{-1}$ and collected at a centre-of-mass energy of $7 rm TeV$ with the LHCb detector, $880 B_s^0 to phiphi$ signal decays are obtained. The CP-violating phase is measured to be in the interval [-2.46, -0.76] rm rad$ at 68% confidence level. The p-value of the Standard Model prediction is 16%.

Measurement of the polarization amplitudes and triple product asymmetries in the B_s^0 -> phi phi decay

Using 1.0 fb^{-1} of pp collision data collected at a centre-of-mass energy of sqrt{s}=7 TeV with the LHCb detector, measurements of the polarization amplitudes, strong phase difference and triple product asymmetries in the B_s^0 -> phi phi decay mode are presented. The measured values are |A_0|^2 = 0.365 +- 0.022 (stat) +- 0.012 (syst), |A_perp|^2 = 0.291 +- 0.024 (stat) +- 0.010 (syst), cos(delta_parallel) = -0.844 +- 0.068 (stat) +- 0.029 (syst), A_U = -0.055 +- 0.036 (stat) +- 0.018 (syst), A_V = 0.010 +- 0.036 (stat) +- 0.018 (syst) .