# Search for Neutral Heavy Leptons Produced in Z Decays

Abstract : Weak isosinglet Neutral Heavy Leptons ($\nu_m$) have been searched for using data collected by the DELPHI detector corresponding to $3.3\times 10^{6}$ hadronic~Z$^{0}$ decays at LEP1. Four separate searches have been performed, for short-lived $\nu_m$ production giving monojet or acollinear jet topologies, and for long-lived $\nu_m$ 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$^0\rightarrow \nu_m \overline{\nu})$ of about $1.3\times10^{-6}$ at 95\% confidence level for $\nu_m$ masses between 3.5 and 50 GeV/$c^2$. Outside this range the limit weakens rapidly with the $\nu_m$ mass. %Special emphasis has been given to the search for monojet--like topologies. One event %has passed the selection, in agreement with the expectation from the reaction: %$e^+e^- \rightarrow\ell \bar\ell \nu\bar\nu$. The results are also interpreted in terms of limits for the single production of excited neutrinos.
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Journal articles

Cited literature [12 references]

http://hal.in2p3.fr/in2p3-00001151
Contributor : Sylvie Flores <>
Submitted on : Wednesday, December 9, 1998 - 10:53:36 AM
Last modification on : Wednesday, September 23, 2020 - 4:33:36 AM
Long-term archiving on: : Friday, May 29, 2015 - 3:21:48 PM

### Identifiers

• HAL Id : in2p3-00001151, version 1

### Citation

P. Abreu, W. Adam, T. Adye, I. Ajinenko, G D. Alekseev, et al.. Search for Neutral Heavy Leptons Produced in Z Decays. Zeitschrift für Physik C Particles and Fields, Springer Verlag, 1997, 74, pp.57-71. ⟨in2p3-00001151⟩

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