Limit on B0s oscillation using a jet charge method

A lower limit is set on the B0s meson oscillation parameter Δms using data collected from 1991 to 1994 by the ALEPH detector. Events with a high transverse momentum lepton and a reconstructed secondary vertex are used. The high transverse momentum leptons are produced mainly by b hadron decays, and the sign of the lepton indicates the particle/antiparticle final state in decays of neutral B mesons. The initial state is determined by a jet charge technique using both sides of the event. A maximum likelihood method is used to set a lower limit of Δms. The 95% confidence level lower limit on Δms ranges between 5.2 and 6.5 (</(c2)) ps-1 when the fraction of b quarks fromZ0 decays that form B0s mesons is varied from 8% to 16%. Assuming that the B0s fraction is 12%, the lower limit would be Δms > 6.1 (</(c2)) ps-1 at 95% confidence level. For xs = ΔmsτBs, this limit also gives xs > 8.8 using the B0s lifetime of τBs = 1.55 +/- 0.11 ps and shifting the central value of τBs down by 1σ.