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.

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DELPHI (DEtector with Lepton, Photon and Hadron Identication) is a detector for e + e physics, designed to provide high granularity o v er a 4 solid angle, allowing an eective particle identication. It has been operating at the LEP (Large Electron-Positron) collider at CERN since 1989. This article reviews its performance.(To be submitted to Nucl. Inst. and Meth.) ii

Cross sections for the reaction pp -• e + e~ have been measured at s = 8.9,12.4, and 13.0 GeV 2 . The cross sections have been analyzed to obtain the proton electromagnetic form factors in the timelike region. We find that GM(Q 2 ) OC q~Aoc 2 {q 2 ) for q 2 > 5 (GeV/c) 2 .The understanding of nucleon structure is one of the central problems of hadronic physics. Measurements of the electric and magnetic form factors, GE and GM> &S functions of the four-momentum transfer q 2 provide experimental information relating to the nucleon structure. A large body of precise data obtained primarily from elastic scattering of electrons by protons and deuterons now exists for these form factors, with the form factors of the proton known up to q 2 = 31 (GeV/c) 2 [1]. However these data are primarily for spacelike momentum transfers (q 2 < 0). Results for GM in the timelike region (s --q 2 c 2 > 0) exist only for a small interval near threshold, 4m 2 c 4 < s < 5.6 GeV 2 . These data include precise measurements recently obtained at the Low Energy Antiproton Ring (LEAR) facility at CERN from the reaction pp -• e + e~ [2]. For larger momentum transfers only upper limits have been established by earlier e + e~ -* pp and pp -> e + e~ experiments [3]. Perturbative QCD predicts [4] that for large momentum transfers Q A \GM\/^Pshould be nearly proportional to the square of the running coupling constant for strong interactions, OL 2 (q 2 ). Recent data [1] for large spacelike momentum transfers are in remarkable agreement with this prediction for q 2 as small as 5 (GeV/c) 2 . It is of great interest to find out if a similar behavior holds for timelike momentum transfers.In this Letter we present the results of our measurements of the cross section for the reactionat y/s = 3.0, 3.5, and 3.6 GeV. These measurements were made as a part of Fermilab experiment E-760, which is dedicated to the study of charmonium by resonant formation in pp annihilations [5]. The differential cross section for process (1) can be expressed in terms of the proton magnetic and electric form factors as [6] da _ 7ra 2 (hc) 2 d(cos<9*) SEP 4772 |G M | 2 (1 + cosV) + -^|O s | 2 sin 2^*where E and P are the center of mass energy and momentum of the antiproton, and 0* is the angle between the e~ and the p in the center of mass system.

The spin density matrix elements for the 0 , K 0 (892) and produced in hadronic Z 0 decays are measured in the DELPHI detector. There is no evidence To be submitted to Physics Letters B ii