LEP Collaborations Research Articles

New particle searches at LEP

Considerable effort has been expended by the LEP collaborations since the start of data taking on the search for new particles and phenomena. Two early results provided evidence that only three families of quarks and leptons exist in nature: the width of the Z established to high precision the existence of only three neutrinos and a direct search for particles belonging to a fourth family proved negative. The search for the mass mechanism of the Standard Model has taken up much effort. Different models predict the existence of one or more Higgs bosons, of supersymmetric particles or of effects arising from compositeness; so far no evidence has been found for any such particles. The paper describes the principles, techniques and results of these searches by the four LEP collaborations. Improvements to some of the published limits, obtained by combining the separate results of the collaborations, are presented.

Neutral current and LEP constraints on an extra E 6 neutral gauge boson. A global fit to electroweak parameters

We perform an analysis of the laboratory constraints on the parameters of an additional neutral gauge boson from the E 6 gauge group. We combine the recent constraints on the mass of the Z as well as its leptonic, hadronic and total decay widths obtained by the four LEP collaborations, with those that follow from deep-inelastic ν μ N scattering and other low energy neutral current experiments, in a global fit. The constraints on the mass and mixing of the Z′ are given for the general unconstrained E 6 model as well as for the case of constrained string models.

Plastic streamer tube calorimeters

The use of streamer tubes in the construction of electromagnetic and hadron calorimeters has been considered by several groups within LEP Collaborations. The results of various tests on these calorimeters is reviewed and the possibility to have an integrated muon-hadron detection system in hadron calorimeters with streamer tubes is discussed, together with possible applications when high energy and high rates are concerned.