Search for a new weakly interacting particle

Fachbereich Physik, Universität Siegen, W-5900 Siegen, FRG
Physics Letters B 06/1991; 262(1):139-147. DOI: 10.1016/0370-2693(91)90657-C


A search for events of the type e+e−→ℓ+ℓ−X0, where X0 can be any weakly interacting particle which couples to the Z, has been performed with the ALEPH detector at LEP, by searching for acollinear lepton pairs. Such particles can be excluded up to a mass of 7.0 GeV/c2 for a value of the ratio of branching fractions, Br(Z→X0l+l−)/Br(Z→l+l−), greater than 2.5 × 10−3 if the X0 has third component of isospin, I3 greater than and decays to a pair of virtual gauge bosons. When this analysis is combined with the previous results of the Higgs particle searches from ALEPH, this limit can be extended to an X0 mass of 60 GeV/c2.

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