Precision measurement of CP violation in $B^0_s \rightarrow J/\psi K^+K^−$ decays

by Roel Aaij (CERN)

Thursday 2 Apr 2015, 11:00 → 12:00 Europe/Zurich

4/2-011 - TH common room (CERN)

The CP-violating phase $\phi_s$ arises in the interference between the amplitude of $B^0_s$ decaying directly to CP eigenstate proceeding via the $b\rightarrow c \bar{c} s$ transition and those decaying after oscillation. The predicted value is small in the SM and effects of New Physics could change its value significantly. The time-dependent CP asymmetry in $B^0_s\rightarrow J/\psi K^+K^-$ decays is measured by LHCb collaboration using pp collision data, corresponding to an integrated luminosity of 3.0fb$^−1$, collected at centre-of-mass energies of 7 and 8TeV. In a sample of 96 000 $B^0_s\rightarrow J/\psi K^+K^-$ decays, the CP-violating phase $\phi_s$ is measured and the value obtained is $\phi_s=-0.058\pm 0.049_{\rm stat}\pm 0.006_{\rm syst}$ rad. This is the most precise single measurement to date. A combined analysis with $B^0_s \rightarrow J/\psi \pi^+\pi^-;$ decays gives $\phi_s=−0.010\pm0.039$ rad. All measurements are in agreement with the Standard Model predictions.

Slides slides.pdf