A lake as a microcosm: reflections on developments in aquatic ecology

In the present study, we aim at relating Forbes' remarkable paper on "The lake as a microcosm", published 125 years ago, to the present status of knowledge in our own research group. Hence, we relate the observations Forbes made to our own microcosm, Lake Krankesjon in southern Sweden, that has been intensively studied by several research groups for more than three decades. Specifically, we focus on the question: Have we made any significant progress or did Forbes and colleagues blaze the trail through the unknown wilderness and we are mainly paving that intellectual road? We conclude that lakes are more isolated than many other biomes, but have, indeed, many extensions, for example, input from the catchment, fishing and fish migration. We also conclude that irrespective of whether lakes should be viewed as microcosms or not, the paper by Forbes has been exceptionally influential and still is, especially since it touches upon almost all aspects of the lake ecosystem, from individual behaviour to food web interactions and environmental issues. Therefore, there is no doubt that even if 125 years have passed, Forbes' paper still is a source of inspiration and deserves to be read. Hence, although aquatic ecology has made considerable progress over the latest century, Forbes might be viewed as one of the major pioneers and visionary scientists of limnology

Study of final state photons in hadronic Z0 decay and limits on new phenomena

The differential cross section for final state radiation from primary quarks is obtained from a study of isolated energetic photons produced in the reaction e+ e- --> Z0 --> hadrons + gamma, as measured in the DELPHI detector at the CERN LEP collider. When combined with the measurement of the total hadronic width of the Z0, the observed rate determines the electroweak coupling constants of up and down type quarks, i.e., upsilon(1/3)2 + a(1/3)2 = 1.13 +/- 0.29 and upsilon(2/3)2 + a(2/3)2 = 1.65 +/- 0.43. No evidence is seen for additional photon production from anomalous decays of the Z0 or from decays of new particles. This measurement leads to upper limits on the production cross section times branching fraction of (a) the Higgs boson in the reaction e+ e- --> Z0 --> H +gamma, H --> hadrons, (b) an excited quark, q* --> q + gamma, and (c) the contribution of an anomalous decay of the Z0 into a photon and hadrons. These limits, all at the 95% confidence level, vary from 3 to 10 pb as the mass of the intermediate state (H, q* or Z*) varies from 10 GeV/c2 to 80 GeV/c2

MULTIPLICITY DEPENDENCE OF MEAN TRANSVERSE-MOMENTUM IN E+E- ANNIHILATIONS AT LEP ENERGIES

A strong increase of the mean transverse momentum [p(t)] with the number of charged particles n(ch) is observed in e+e- annihilations into hadrons at LEP energies, The effect resembles correlations observed in hadron-hadron interactions. In e+e- annihilations the [p(t)] and n(ch) correlations can be accounted for by gluon radiation

A MEASUREMENT OF THE LIFETIME OF THE TAU-LEPTON

The lifetime of the tau lepton has been measured by two independent methods using a silicon microvertex detector installed in the DELPHI detector. The signed impact parameter distribution of the one prong decays yielded a lifetime of tau-tau = 321 +/- 36 (stat.) +/- 16 (syst.) fs, while the decay length distribution of three prong decays gave the result tau-tau = 310 +/- 31 (stat. ) +/- 9 (syst.) fs. The final value of the combined result was tau-tau = 314 +/- 25 fs. The ratio of the Fermi coupling constant from tau decay relative to that from muon decay was found to be 0.95 +/- 0.04, compatible with the hypothesis of lepton universality

SEARCH FOR SCALAR LEPTOQUARKS FROM Z(0) DECAYS

We have searched for pair produced scalar leptoquarks each decaying to a quark and a charged lepton in a sample of 116 000 hadronic Z0 events produced at LEP. No candidate was detected and cross section and branching ratio limits are set for the above process at 95% CL. Mass limits are found to be about 42 GeV/c2 depending only slightly on the models used and a coupling times branching ratio exclusion line is drawn for a scalar leptoquark with a free coupling. We have also probed the mass region above 45 GeV/c2 for a singly produced scalar leptoquark and set limits on the cross section and the coupling lambda(2)/4-pi up to 60 GeV

MEASUREMENT OF THE AVERAGE LIFETIME OF B-HADRONS

The average lifetime of B hadrons produced in hadronic Z0 decays has been measured with the DELPHI detector at LEP. The measurement is based on the analysis of the impact parameter distribution of high p(t) muons and hadrons. The resulting mean B lifetimes are tau(B) = (1.30 +/- 0.10 +/- 0.08) ps and tau(B) = (1.27 +/- 0.04 +/- 0.12) ps respectively, giving a combined value of tau(B) = (1.28 +/- 0.10) ps. The hadronic sample was also used to measure the partial Z0 width GAMMA(bbBAR)/GAMMA(h) and gave a value of 0.222(-0.031)+0.033 +/- 0.017

Production rate and decay lifetime measurements of B(s)0 mesons at LEP using D(s) and phi mesons

The study of the properties of inclusive production ofD s mesons and of events in which a ϕ and a muon are present in the same jet provides two independent measurements of the probability,f s w , for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ 0 decays. The combined value of these measurements isf s w =0.19±0.06±0.08. From the flight distance distributions ofD s and of (ϕ-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theB s 0 meson lifetime. Combining these measurements with a previous result based on the study ofD s-μ events, theB s 0 meson lifetime is measured to be: 0.96±0.37 ps