Study of $B_{s}$ oscillations

This document contains two ALEPH Reports on three different analyses of $B_{s}$ oscillations, based on the statistics collected by the ALEPH experiment during 1991-1995. $B_{s}$ mesons are fully reconstructed in several hadronic decay channels, yielding a small sample of candidates with excellent decay length and momentum reconstruction. Semileptonic decays with a fully recontructed $D_{s}$ meson yield larger statistics with equally high $B_{s}$ purity, but somewhat degraded momentum resolution. Inclusive semileptonic decays of b hadrons yield the highest sensitivity to $B_{s}$ oscillations, due to the much higher statistics. The combination of the above three with the other ALEPH analyses gives a limit of $\Delta m_{s} > 10.7$ ps$^{-1}$ at 95% C.L. with a sensitivity equal to $13.1$ ps$^{-1}$.