Two-axigluon decay of the Z0

In the realm of the chiral color model, we compute the decay widths of the Z⁰ into two axigluons as a function of the axigluon mass. The results indicate that an axigluon with a mass under 41 GeV should be clearly detectable at LEP or SLC.     

B* production in Z0 decays

The process B*→Bγ has been observed in a sample of approximately 4.1 million hadronic Z⁰ decays collected by the OPAL detector at LEP in the years 1991–1995. Inclusively reconstructed B mesons have been combined with converted photons to reconstruct approximately 1900 B* mesons. The B*–B mass difference is found to be ΔM(B* ?B) = 46.2 ± 0.3 ± 0.8 MeV/c ², and the rate of B* meson production relative to that of B mesons is found to be σ _B*/σ _B = 0.760 ± 0.036 ± 0.083, where the first errors are statistical and the second systematic. The angular distribution of the transition photon in the B* rest frame has been measured and the relative contribution of longitudinal B* polarization states found to be σ _l/(σ _l + σ _t ) = 0.36 ± 0.06 ± 0.07, consistent with a simple spin counting picture. These results average over B⁰, B± and B _s ⁰ mesons.     

THE MIXEFIFNECTG OF Z0 AND TOPONIUN

It is shown that the mixing effect between the Z⁰ and the toponium will significantly affect various properties of toponium state.     

Measurement of inclusive π0 production in hadronic Z 0 decays

An analysis is presented of inclusive π⁰ production in Z ⁰ decays measured with the DELPHI detector. At low energies, π⁰ decays are reconstructed by using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to $x_p={2cdot p?/{sqrt s}=0.75}$) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for qq? and bb? events. The number of π⁰’s per hadronic Z ⁰ event is $N(?^0)/Z_{had} ^0=9.2pm 0.2({? stat})pm 1.0 ({? syst})$ and for bb? events the number of π⁰’s is ${? N}(?^0)/{? b?r b}=10.1pm 0.4({? stat})pm 1.1 ({? syst})$. The ratio of the number of π⁰’s in bb? events to hadronic Z ⁰ events is less affected by the systematic errors and is found to be 1.09 ±0.05 ±0.01. The measured π⁰ cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the $xi_{? p}={? ln}(1/{? x_p})$ distribution is $xi_p^{?ar}=3.90_{-0.14}^{+0.24}.$ The average number of π⁰’s from the decay of primary B hadrons is found to be N(B → π⁰ X)/B hadron = 2.78 ± 0.15(stat) ± 0.60(syst).     

Evolution effects in Z0 fragmentation into Charmonium

In Z⁰ decay into prompt charmonium, i.e. charmonium not originating from B-meson decays, the most important contribution is expected to come from colour-octet mechanisms. However, previous fixed-order calculations of the colour-octet contribution contain large logarithms which, in a more complete treatment, should be resummed to all orders. We study this resummation by using a Monte Carlo QCD cascade model and find that the fixed-order colouroctet result is diminished by 15%. We compare the Monte Carlo calculations with results obtained by using analytical evolution equations.     

Strange baryon production in hadronic Z0 decays

The production of the $J^{P}={1?er 2}^{+}$ octet baryons Λ and Ξ^?, the $J^{P}={3?er 2}^{+}$ decuplet baryons Σ(1385)^±Ξ(1530)⁰, and Ω^?, and the $J^{P}={3?er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z⁰ decays. The integrated rates and the differential cross-sections as a function of x _E, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ^? baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ^?, Σ(1385)^±Ξ(1530)⁰, and Λ(1520) are also compared to the predictions of an analytical QCD formula.     

Signals of supersymmetry at the Z0 resonance

The Z⁰ boson can have a sizeable branching ratio into a pair of neutralinos (the fermionic superpartners of the neutral gauge and Higgs bosons). All the subsequent decays of the heavier neutralinos lead to very distinctive signatures in e⁺e⁻ collisions at the Z⁰ pole. This may even be an efficient way to produce the Higgs boson. We study the various branching ratios as functions of the parameters of the underlying supersymmetric theory, making no ad hoc assumptions on the actual composition of the physical neutralino states.