Speaker
Description
A search for the rare B_(s)^0 \to \mu^+ \mu^- \mu^+ \mu^- decays is presented using proton-proton collision data collected by the CMS experiment at \sqrt{s} = 13.6 TeV between 2022 and 2024, corresponding to an integrated luminosity of 170 fb^{-1}. These Cabibbo-suppressed flavor-changing neutral current processes are highly suppressed in the Standard Model and are sensitive to potential new physics contributions in short-distance b \to s\ell^+\ell^- transitions.
Signal candidates are reconstructed in fully identified four-muon final states and normalized to the kinematically similar B_s^0 \to J/\psi(\mu^+\mu^-)\,\phi(\mu^+\mu^-) decay. A combination of optimized selections on muon quality, vertexing, and kinematics, together with machine learning classifiers, is employed to efficiently suppress combinatorial background while maintaining high signal efficiency.
No significant excess above the expected background is observed, and upper limits are set on the corresponding branching fractions, representing the most stringent constraints to date and providing a solid basis for future studies aimed at further constraining the Wilson coefficients governing b \to s \ell^+\ell^- transitions.