Measurement of the weak mixing phase $\phi_s$ through time-dependent $CP$ violation in $B_s^0 \rightarrow J/\psi\phi$ decay in ATLAS

In the Standard Model of particle physics, $CP$ violation arises due to a single complex phase in the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix. Testing the validity of the CKM mechanism as the only source of $CP$ violation is one of the major experimental challenges in particle physics today. Precise measurement of the CKM parameters therefore constrains the Standard Model, and may reveal effects beyond the Standard Model. Measurement of the time-dependent decay rates of $B_s^0 \rightarrow J/\psi\phi$ provides a theoretically clean method for extracting $CP$-violating weak mixing phase $\phi_s$. The Standard Model predicts $\phi_s$ to be very small and it is very well constrained, while in many new physics models large $\phi_s$ values are expected. $B_s^0 \rightarrow J/\psi\phi$ decay channel is sensitive to the new physics contributions, and already small deviations in a measurement of $\phi_s$ would be hints for the existence of the new particles. The most recent results from ATLAS are presented in $CP$-violating mixing phase $\psi_s$ and several other parameters describing the $B_s^0$ meson system.