This paper presents recent time-dependent measurements of neutral B meson oscillations. Similar to the $K^0$--$\bar{ K}^0$ system, there are two such systems involving the b quark: $B_d^0$--$\bar{ B}_d^0$ and $B_s^0$--$\bar{ B}_s^0$. Thus the physical states are respectively $K_{ S}$ and $K_{ L}$, $(B_d)_S$ and $(B_d)_L$, and $(B_s)_S$ and $(B_s)_L$. The oscillation between each pair of states can be used to determine their mass difference. The present world average for the $(B_d)_S$--$(B_d)_L$ mass difference is $\Delta m_d = 0.457\pm0.019 ps^{ -1}$ (or $(3.01\pm0.13)\times 10^{ -4}$ eV). Using $f_{ B_s}$ = 12\% (the fraction of $B_s$ produced in b events), the current lower limit on the corresponding $\Delta m_s$ is 6.1 ps$^{ -1}$ (or $4.0\times 10^{ -3}$ eV).
Categories: hep-ex