Experimental limits on quantum decoherence from $B$ meson systems

Neutral $B$-meson systems serve as critical tests of the Standard Model and play a key role in limiting its extensions. While these systems are typically studied under the assumption of perfect quantum coherence, interactions with the environment can lead to decoherence. Such decoherence effects can obscure the measured values of key parameters such as the oscillation frequency $\Delta m$ and $CP$-violating parameter $\sin 2\beta$. Using the experimental data, we present the first combined analysis of mixing asymmetry and $CP$-asymmetry measurements for $B_d$-mesons, which indicates that $\lambda_d$ is non-zero at approximately $6 \,\sigma$. We also establish the first experimental constraints on the decoherence parameter $\lambda_s$ for $B_s$-mesons, finding it to be non-zero at $3 \,\sigma$.