We search for neutral heavy leptons that are isosinglets under the standard SU (2)l gauge group. Such neutral heavy leptons are expected in many extensions of the standard model. Three types of heavy leptons Ne, N^, NT associated with the three neutrino types v* have been directly searched for and no evidence for a signal has been found. We set the limit Br(Z° -► z//N*) < 3 x 10" 5 at the 95% CL for the mass range from 3 GeV up to m%.

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We present a study of the inclusive production of neutral pions and charged particles from 112 000 hadronic Z° decays. The measured inclusive momentum distributions can be reproduced by parion shower Monte Carlo programs and also by an analytical QCD calculation. Comparing our results to e+e" data between ^= 9 and 91 GeV, we find that the evolution of the spectra with center of mass energy is consistent with the QCD predictions.

General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 12 May 2018Physics Letters B 271 ( 1991 ) We have measured the ratio of the strong coupling constants as for bottom quarks and light quarks at the Z ° resonance, in order to test the flavour independence of the strong interaction. The coupling strength oq has been determined from the fraction of events with three jets, measured for a sample of all hadronic events, and for inclusive muon and electron events. The b purity is evaluated to be 22% for the first data set and 87% for the inclusive lepton sample. We find cq(b)/as(udsc)=l.O0+ 0.05 (stat.) + 0.06 (syst.).

Citation for published version (APA):Adriani, O., Aguilar-Benitez, M., Ahlen, S. P., Alcaraz, J., Aloisio, A., Alverson, G., ... Linde, F. L. (1992). Determination of alpha-s from hadronic event shapes measured on the Z0 resonance. Physics Letters B, 284, 471-481. DOI: 10.1016/0370-269390463-E General rightsIt is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), other than for strictly personal, individual use, unless the work is under an open content license (like Creative Commons). Disclaimer/Complaints regulationsIf you believe that digital publication of certain material infringes any of your rights or (privacy) interests, please let the Library know, stating your reasons. In case of a legitimate complaint, the Library will make the material inaccessible and/or remove it from the website. Please Ask the Library: http://uba.uva.nl/en/contact, or a letter to: Library of the University of Amsterdam, Secretariat, Singel 425, 1012 WP Amsterdam, The Netherlands. You will be contacted as soon as possible. Download date: 09 May 2018Physics Letters B 284 (1992) We present a study of the global event shape variables thrust and heavy jet mass, of energy-energy correlations and of jet multiplicities based on 250 000 hadronic Z ° decays. The data are compared to new QCD calculations including resummation of leading and next-to-leading logarithms to all orders. We determine the strong coupling constant c~s (91.2 GeV) = 0.125 + 0.003 (exp) + 0.008 (theor). The first error is the experimental uncertainty. The second error is due to hadronization uncertainties and approximations in the calculations of the higher order corrections.

We have searched for direct leptoquark production in Z ° decays from a scan of the Z ° resonance, in the energy range 88.2 ~< x/] ~< 94.2 GeV, using 5.2 pb-~ of data. We exclude the existence of scalar leptoquarks with masses less than 41 to 44 GeV, depending on the charge assignments, at the 95% confidence level.

We search for new resonances, Y, with mass, My, in the range from 30 to 89 GeV, produced via the reaction e+e-,Z°-,),Y, where Y subsequently decays into e + e-, IX +Ix-or hadrons. We use 5.5. pb-1 of data collected in the energy range 88.2 ~ x/~ ~< 94.2 GeV, near the Z ° peak. We obtain the following upper limits, at the 95% confidence level, on the product of the branching ratios: BR(Z°-,~/Y)XBR(Y-.e+e-)<2.8×10-4 for 30

We search for J=ψ radiative decays into a weakly interacting neutral particle, namely an invisible particle, using the J=ψ produced through the process ψð3686Þ → π þ π − J=ψ in a data sample of ð448.1 AE 2.9Þ × 10 6 ψð3686Þ decays collected by the BESIII detector at BEPCII. No significant signal is observed. Using a modified frequentist method, upper limits on the branching fractions are set under different assumptions of invisible particle masses up to 1.2 GeV=c 2. The upper limit corresponding to an invisible particle with zero mass is 7.0 × 10 −7 at the 90% confidence level.