Measurement of the CP violation phase $\phi_s$ in $B_s^0 \rightarrow J/ \psi \phi$ decay in ATLAS using 80.5 $fb^{-1}$ of LHC data at 13 TeV

Measurement of the weak mixing phase phi_s through time-dependent CP violation in Bs0—>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 Bs0—>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. Bs0—>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. A measurement of the B0s decay parameters in Bs0—>J/psi phi channel using an integrated luminosity of 80.5 fb−1 collected by the ATLAS detector from 13 TeV pp collisions at the LHC is presented. The measured parameters include the CP-violating phase phi_s, the width difference ∆Γs between the mass eigenstates and the average decay width Γs.