The Permian-Triassic boundary and Early Triassic sedimentation in Western European basins: an overview

At the scale of the peri-Tethyan basins of western Europe, the “Buntsandstein” continental lithostratigraphic units are frequently attributed to the “Permian-Triassic” because, in most cases, the lack of any “Scythian” (i.e. Early Triassic) biochronological evidence makes it very difficult to attribute the basal beds of the cycle to the Permian or to the Triassic. A careful recognition of unconformities and sedimentary indications of clearly arid climate provide powerful tools for correlation within non-marine successions that are devoid of any biostratigraphic markers, at least on the scale of the West European Plate. From a review of the “Buntsandstein” series of several basins we can characterize the Permian-Triassic boundary and the beginning of Triassic sedimentation at the scale of Western Europe. We clearly show that, except for the Central Germanic Basin, an unconformity can be observed between the Permian and the Triassic. Apart from the Germanic Basin, there is a total lack of typically “Scythian” fossils in the rest of West European basins, and the oldest biochronological markers yielded by these units are palynomorphs allowing to assign an Anisian age generally to the upper part of the “Buntsandstein”, but also its lowermost in a few cases. In the peri-Tethyan basins of western Europe, the Permian-Triassic boundary corresponds to an unconformity overlain by conglomerates containing ventifacts (followed by fluvial sandstones, sometimes rich in paleosols and sometimes totally devoid), which are attributed mainly to the lower Olenekian, i.e. Smithian. Alternatively, the succession passes up directly into fluvial sandstones containing the first paleosols, and then plant debris and palynomorphs attributed to the Anisian. In this way, the lack of typically Early Triassic fossils in most of the peri-Tethyan basins, at the scale of the west European Plate, can be explained by a true stratigraphic hiatus in the earliest Triassic (i.e. Induan) and by arid conditions unfavourable for the development of flora and fauna and their preservation during the Olenekian.En las cuencas peritéthicas de Europa occidental, la unidad litoestratigráfi ca continental “Buntsandstein” es frecuentemente atribuida al “Pérmico-Triásico”, porque, en la mayoría de los casos, la falta de elementos biocronológicos “scythienses” complica la atribución de los niveles basales al Pérmico o al Triásico. Un cuidadoso examen de las discordancias, y el uso de indicadores sedimentarios de climas claramente áridos constituyen herramientas fundamentales para la correlación de estas unidades no marinas, desprovistas de cualquier marcador bioestratigráfi co, al menos en el Oeste de la Placa Europea. La revisión de las series “Buntsandstein” de varias cuencas nos ha permitido caracterizar el límite Pérmico-Triásico y el comienzo de la sedimentación durante el Triásico inferior en el oeste de Europa, demostrando claramente que, excepto en la Cuenca Germánica Central, se puede observar una discordancia entre las series pérmicas y triásicas. Excepto en esta Cuenca Germánica, existe una falta total de fósiles típicamente “scythienses”, y los elementos bioestratigráfi cos más antiguos encontrados son conjuntos de palinomorfos que permiten asignar a los niveles superiores de las series “Buntsandstein” una edad Anisiense, en algunos cortes los niveles inferiores. En las cuencas peritéthicas de Europa occidental, el límite Pérmico-Triásico se corresponde con una discordancia que se recubre por conglomerados con ventifactos (seguidos por areniscas fl uviales, a veces ricas en paleosuelos y a veces totalmente desprovistas de ellos), atribuidos principalmente al Olenekiense inferior (Smithiense), o directamente areniscas fluviales donde aparecen los primeros paleosuelos, así como restos de plantas y palinomorfos, atribuidos al Anisiense. De esta forma en el Oeste de la Placa Europea, la falta de fósiles característicos del Triásico Inferior, en la mayoría de las cuencas perithéticas, puede explicarse por un importante hiato estratigráfi co durante el Triásico Inferior (Induense) y por unas condiciones áridas, desfavorables para la vida y la preservación de fósiles durante el Olenekiense

Measurement of the W+W-gamma Cross Section and Direct Limits on Anomalous Quartic Gauge Boson Couplings at LEP

The process e+e- -> W+W-gamma is analysed using the data collected with the L3 detector at LEP at a centre-of-mass energy of 188.6GeV, corresponding to an integrated luminosity of 176.8pb^-1. Based on a sample of 42 selected W+W- candidates containing an isolated hard photon, the W+W-gamma cross section, defined within phase-space cuts, is measured to be: sigma_WWgamma = 290 +/- 80 +/- 16 fb, consistent with the Standard Model expectation. Including the process e+e- -> nu nu gamma gamma, limits are derived on anomalous contributions to the Standard Model quartic vertices W+W- gamma gamma and W+W-Z gamma at 95% CL: -0.043 GeV^-2 < a_0/Lambda^2 < 0.043 GeV^-2 0.08 GeV^-2 < a_c/Lambda^2 < 0.13 GeV^-2 0.41 GeV^-2 < a_n/Lambda^2 < 0.37 GeV^-2

Production of Single W Bosons at \sqrt{s}=189 GeV and Measurement of WWgamma Gauge Couplings

Single W boson production in electron-positron collisions is studied with the L3 detector at LEP. The data sample collected at a centre-of-mass energy of \sqrt{s} = 188.7GeV corresponds to an integrated luminosity of 176.4pb^-1. Events with a single energetic lepton or two acoplanar hadronic jets are selected. Within phase-space cuts, the total cross-section is measured to be 0.53 +/- 0.12 +/- 0.03 pb, consistent with the Standard Model expectation. Including our single W boson results obtained at lower \sqrt{s}, the WWgamma gauge couplings kappa_gamma and lambda_gamma are determined to be kappa_gamma = 0.93 +/- 0.16 +/- 0.09 and lambda_gamma = -0.31 +0.68 -0.19 +/- 0.13

Search for an invisibly decaying Higgs boson in e^+e^- collisions at \sqrt{s} = 183 - 189 GeV

A search for a Higgs boson decaying into invisible particles is performed using the data collected at LEP by the L3 experiment at centre-of-mass energies of 183 GeV and 189 GeV. The integrated luminosities are respectively 55.3 pb^-1 and 176.4 pb^-1. The observed candidates are consistent with the expectations from Standard Model processes. In the hypothesis that the production cross section of this Higgs boson equals the Standard Model one and the branching ratio into invisible particles is 100%, a lower mass limit of 89.2 GeV is set at 95% confidence level

Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV

A search for the lightest neutral scalar and neutral pseudoscalar Higgs bosons in the Minimal Supersymmetric Standard Model is performed using 176.4 pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of 189 GeV. No signal is observed, and the data are consistent with the expected Standard Model background. Lower limits on the masses of the lightest neutral scalar and pseudoscalar Higgs bosons are given as a function of tan(beta). Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h > 77.1 GeV and m_A > 77.1 GeV

Measurement of Bose-Einstein Correlations in e+e- -> W+W- at root(s)=189GeV

We investigate Bose-Einstein correlations (BEC) in W-pair production at root(s)=189GeV using the L3 detector at LEP. We observe BEC between particles from a single W decay in good agreement with those from a light-quark Z decay sample. We investigate their possible existence between particles coming from different W's. No evidence for such inter-W BEC is found

Measurement of the Lifetime of the Tau Lepton

The tau lepton lifetime is measured with the L3 detector at LEP using the complete data taken at centre-of-mass energies around the Z pole resulting in tau_tau = 293.2 +/- 2.0 (stat) +/- 1.5 (syst) fs. The comparison of this result with the muon lifetime supports lepton universality of the weak charged current at the level of six per mille. Assuming lepton universality, the value of the strong coupling constant, alpha_s is found to be alpha_s(m_tau^2) = 0.319 +/- 0.015(exp.) +/- 0.014 (theory)

Search for Extra Dimensions in Boson and Fermion Pair Production in e+e- Interactions at LEP

Extra spatial dimensions are proposed by recent theories that postulate the scale of gravity to be of the same order as the electroweak scale. A sizeable interaction between gravitons and Standard Model particles is then predicted. Effects of these new interactions in boson and fermion pair production are searched for in the data sample collected at centre-of-mass energies above the Z pole by the L3 detector at LEP. In addition, the direct production of a graviton associated with a Z boson is investigated. No statistically significant hints for the existence of these effects are found and lower limits in excess of 1 TeV are derived on the scale of this new theory of gravity

Measurement of the Probability of Gluon Splitting into Charmed Quarks in Hadronic Z Decays

We have measured the probability, n(g->cc~), of a gluon splitting into a charm-quark pair using 1.7 million hadronic Z decays collected by the L3 detector. Two independent methods have been applied to events with a three-jet topology. One method relies on tagging charmed hadrons by identifying a lepton in the lowest energy jet. The other method uses a neural network based on global event shape parameters. Combining both methods, we measure n(g->cc~)= [2.45 +/- 0.29 +/- 0.53]%

Measurement of Triple-Gauge-Boson Couplings of the W Boson at LEP

We report on measurements of the triple-gauge-boson couplings of the W boson in e+e- collisions with the L3 detector at LEP. W-pair, single-W and single-photon events are analysed in a data sample corresponding to a total luminosity of 76.7 pb^{-1} collected at centre-of-mass energies between 161 GeV and 183 GeV. CP-conserving as well as both C- and P-conserving triple-gauge-boson couplings are determined. The results, in good agreement with the Standard-Model expectations, confirm the existence of the self coupling among the electroweak gauge bosons and constrain its structure