A search for neutral Higgs bosons has been performed using the full sample of Z 0 decays collected by the OPAL detector at LEP up to 1995. The data were taken at centre-of-mass energies between 88 GeV and 95 GeV and correspond to an integrated luminosity of approximately 160 pb 1. The present search addresses the processes Z 0 !H 0 Z and h 0 Z , where H 0 is the Higgs boson predicted by the Standard Model and h 0 the lightest neutral scalar Higgs boson predicted in the framework of the Minimal Supersymmetric Standard Model. For the virtual Z 0 boson, Z , the following decay c hannels are considered: Z ! , e + e and +. One candidate event

An event sample enriched in semileptonic decays of b hadrons is selected using an inclusive lepton selection from approximately 3.0 million hadronic Z 0 decays collected with the OPAL detector. This sample is used to investigate B meson oscillations by reconstructing a proper decay time for the parent of each lepton, using a jet charge method to estimate the production flavour of this parent, and using the lepton charge to tag the decay flavour. We measure the mass difference between the two B 0 d mass eigenstatesFor the B 0 s system, we find ∆m s > 3.1 ps −1 at the 95% confidence level. This limit varies only a little if alternative limit setting approaches are adopted. Regions at higher ∆m s values are also excluded with some methods for setting the limit.By studying the charge symmetry of the B 0 d mixing structure, we are able to constrain possible CP and CPT violating effects. We measure the CP violation parameter Re ǫ B = −0.006 ± 0.010 ± 0.006 and the indirect CPT violating parameter Im δ B = −0.020 ± 0.016 ± 0.006 . If we invoke CPT symmetry, then we obtainRe ǫ B = 0.002 ± 0.007 ± 0.003 .

A search for a supersymmetric partner of the top quark (t 1 ) has been performed by the OPAL experiment i n e + e collisions at LEP. The integrated luminosity of the data sample analysed was 69.1 pb 1 , which corresponds to 1.6810 6 produced Z 0 ! q q e v ents. Not 1 candidates have been found. This study excludes the existence of thet 1 with a mass below 45.1 GeV at 95% C.L., where the mixing angle of left-and right-handed partners is smaller than 0.85 rad or greater than 1.15 rad, and the mass dierence between thet 1 and the lightest neutralino is greater than 5 GeV.

The production rates of D * ± mesons in charm and bottom events at centre-of-mass energies of about 91 GeV and the partial width of primary cc pairs in hadronic Z 0 decays have been measured at LEP using almost 4.4 million hadronic Z 0 decays collected with the OPAL detector between 1990 and 1995. Using a combination of several charm quark tagging methods based on fully and partially reconstructed D * ± mesons, and a bottom tag based on identified muons and electrons, the hadronisation fractions of charm and bottom quarks into D * ± mesons have been found to be f (b → D * + X) = 0.173 ± 0.016 ± 0.012 and f (c → D * + X) = 0.222 ± 0.014 ± 0.014 .The fraction of cc events in hadronic Z 0 decays, Γ cc /Γ had = Γ(Z 0 → cc)/Γ(Z 0 → hadrons), is determined to be Γ cc /Γ had = 0.180 ± 0.011 ± 0.012 ± 0.006 .In all cases the first error is statistical, and the second one systematic. The last error quoted for Γ cc /Γ had is due to external branching ratios.

The longitudinal polarization, the transverse polarization, and the forward-backward asymmetry of Λ baryons, have been measured using a sample of 4.34 million hadronic Z 0 decays collected with the OPAL detector at LEP between 1990 and 1995. These results are important as an aid to the understanding of hadronization mechanisms. Significant longitudinal polarization has been observed at intermediate and high momentum. For x E (≡ 2E Λ / √ s) > 0.3, the longitudinal polarization has been measured to be −32.9 ± 5.5 (stat) ± 5.2 (syst)%. We have observed no transverse polarization. A significant forward-backward asymmetry has been measured and can be described by a JETSET model.