The Standard Model of Particle Physics precisely predicts the cross-sections for the processes $B_s \rightarrow \mu\mu$ and $B_d \rightarrow \mu\mu$ which are suppressed in the SM. Beyond SM (BSM) contribution can enhance the decay rates. Precise measurement of branching fractions and of the $B_s \rightarrow \mu\mu$ decay effective lifetime is of prime concern for experiments like CMS in the quest for new physics. The SM also precisely predicts the CP violating phase $\phi_s$ in the $B_s \rightarrow \phi\phi \rightarrow$ 4 Kaons decay, a significant deviation from the SM prediction would provide a clear signature for BSM. During the High Luminosity (HL) period of the LHC, also known as LHC Phase-2, which will start from 2026, CMS will tr...