Illustration: Carin Cain

Figure 1: (Top) Proton-antiproton ($pp¯$) collisions sometimes create a $Bs0$-$B¯s0$ pair among the spray of new particles. Subsequent decays may then produce muons: a $μ+$ from $Bs0$, or a $μ-$ from $B¯s0$. Due to the possibility for a $B¯s0$ to “oscillate”—transmute—into a $Bs0$, and vice versa, muons of the same electric charge can be produced. Finally, comparing $μ+μ+$ (as shown) to $μ-μ-$ (the $CP$-mirrored process, with matter and antimatter inverted) reveals if these oscillations display a $CP$ asymmetry. (Bottom) The weak interaction, mediated by $W$ bosons, can change any quark with electric charge −$1/3$ ($d,s,b$ quarks) into any quark with electric charge $+2/3$ ($u,c,t$ quarks) and vice versa. As time flows from left to right in the diagram above, the successive exchange of two $W$ bosons allows a $B¯s0$ to oscillate into its antimatter partner, a $Bs0$. The standard model also predicts a small $CP$ asymmetry in these oscillations. It would not be surprising for physics beyond the standard model to include new particles which can mediate the oscillations, and hence alter the predicted asymmetry, allowing us to indirectly discern their existence.