Link to publication Citation for published version (APA):Abreu, P., Boudinov, E., Holthuizen, D. J., Kjaer, N. J., Kluit, P. M., Mulders, M. P., ... van Eldik, J. E. (1997). Search for neutral heavy leptons produced in $Z$ decays. Zeitschrift für Physik. C, Particles and Fields, 74, 57. DOI: 10.1007/s002880050370 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 2018 Z. Phys. C 74, 57-71 (1997) ZEITSCHRIFT FÜR PHYSIK C Abstract. Weak isosinglet Neutral Heavy Leptons (ν m ) have been searched for using data collected by the DEL-PHI detector corresponding to 3.3 × 10 6 hadronic Z 0 decays at LEP1. Four separate searches have been performed, for short-lived ν m production giving monojet or acollinear jet topologies, and for long-lived ν m giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z 0 → ν m ν) of about 1.3 × 10 −6 at 95% confidence level for ν m masses between 3.5 and 50 GeV/c 2 . Outside this range the limit weakens rapidly with the ν m mass. The results are also interpreted in terms of limits for the single production of excited neutrinos.

Using the entire CLEO-c c ð3770Þ ! D " D event sample, corresponding to an integrated luminosity of 818 pb À1 and approximately 5:4 Â 10 6 D " D events, we present a study of the decays D 0 ! À e þ e , D 0 ! K À e þ e , D þ ! 0 e þ e , and D þ ! " K 0 e þ e . Via a tagged analysis technique, in which one D is fully reconstructed in a hadronic mode, partial rates for semileptonic decays by the other D are measured in several q 2 bins. We fit these rates using several form factor parametrizations and report the results, including form factor shape parameters and the branching fractions BðD 0 ! À e þ e Þ ¼ ð0:288 AE 0:008 AE 0:003Þ%, BðD 0 ! K À e þ e Þ ¼ ð3:50 AE 0:03 AE 0:04Þ%, BðD þ ! 0 e þ e Þ ¼ ð0:405 AE 0:016 AE 0:009Þ%, and BðD þ ! "K 0 e þ e Þ ¼ ð8:83 AE 0:10 AE 0:20Þ%, where the first uncertainties are statistical and the second are systematic. Taking input from lattice quantum chromodynamics, we also find jV cd j ¼ 0:234 AE 0:007 AE 0:002 AE 0:025 and jV cs j ¼ 0:985 AE 0:009 AE 0:006 AE 0:103, where the third uncertainties are from lattice quantum chromodynamics.

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Using 20.7 pb −1 of e + e − annihilation data taken at √ s = 3.671 GeV with the CLEO-c detector, precision measurements of the electromagnetic form factors of the charged pion, charged kaon, and proton have been made for timelike momentum transfer of |Q 2 | = 13.48 GeV 2 by the reaction e + e − → h + h − . The measurements are the first ever with identified pions and kaons of |Q 2 | > 4 GeV 2 , with the results F π (13.48 GeV 2 ) = 0.075 ± 0.008(stat) ± 0.005(syst) and F K (13.48 GeV 2 ) = 0.063±0.004(stat)±0.001(syst). The result for the proton, assumingGeV 2 ) = 0.014 ± 0.002(stat) ± 0.001(syst), which is in agreement with earlier results.