Search for anomalous production of di-lepton events with missing transverse momentum in e(+)e(-) collisions at root s = 161 and 172 GeV

Events containing a pair of charged leptons and significant missing transverse momentum are selected from a data sample corresponding to a total integrated luminosity of 20.6 pb^-1 at centre-of-mass energies of 161 GeV and 172 GeV. The observed number of events, four at 161 GeV and nine at 172 GeV, is consistent with the number expected from Standard Model processes, predominantly arising from W+W- production with each W decaying leptonically. This topology is also an experimental signature for the pair production of new particles that decay to a charged lepton accompanied by one or more invisible particles. Further event selection criteria are described that optimise the sensitivity to particular new physics channels. No evidence for new phenomena is observed and limits on the production of scalar charged lepton pairs and other new particles are presented

Tests of the standard model and constraints on new physics from measurements of fermion-pair production at 130-172GeV at LEP

Production of events with hadronic and leptonic final states has been measured in e(+)e(-) collisions at centre-of-mass energies of 130-172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z gamma events, and compared to Standard Model expectations. The ratio R-b of the cross-section for production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of gamma-Z interference. The energy dependence of alpha(em) has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for t-channel contributions from new massive particles and to place limits on gaugino pair production with subsequent decay of the gaugino into a light gluino and a quark pair

Search for unstable heavy and excited leptons in e(+)e(-) collisions at root s=170-172 GeV

We have searched for unstable neutral and charged heavy leptons, N and L+/-, and for excited states of neutral and charged leptons, v*, e*, mu* and tau*, in e(+)e(-) collisions at centre-of-mass energies of 170 and 172 GeV using the OPAL detector at LEP. No evidence for their existence was found. Front the analysis of charged-current decays of pair-produced unstable heavy leptons, and of charged-current and photonic decays of pair-produced excited leptons, lower limits on their masses are derived. From the analysis of charged-current and photonic decays of singly-produced excited leptons, upper Limits on the ratio of the coupling to the compositeness scale, f/A, are determined for masses up to the kinematic limit

Search for CP violation in Z0 ---> tau+ tau- and an upper limit on the weak dipole moment of the tau lepton

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