Search for a new weakly interacting particle

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

Measurement of the forward - backward asymmetry in Z ---> b anti-b and Z ---> c anti-c

From a sample of 150 000 hadronic Z decays collected with the ALEPH detector at LEP, events containing prompt leptons are used to measure the forward-backward asymmetries for the channels and , giving the results AFBb=0.126±0.028±0.012 and AFBc=0.064±0.039±0.030. These asymmetries correspond to the value of effective electroweak mixing angle at the Z mass sin2θW(mZ2) = 0.2262±0.0053

Charged particle pair production associated with a lepton pair in Z decays: Indication of an excess in the tau channel

In a sample of 200 000 Z decays, events with two leptons and an additional pair of charged particles are studied. The 35 events found show a possible excess in the tau channel compared with the expectation from electroweak processes. The features of the events are consistent with radiation of virtual photons