Results of a search for the pair production of charged heavy leptons in e+e- annihilations over the center-of-mass energy range of 50 to 60.8 GeV are reported. We assume that the leptons are of the sequential type but have allowed for the case where the associated neutrino might be massive. Separate searches for evidence for decays to hadronic and leptonic final states, searches specialized for the case where the charged lepton and its associated neutrino are close in mass, and a search for stable heavy leptons have uncovered no evidence for the production of such particles at these energies. Mass limits for heavy leptons and their associated neutrinos are determined for a range of hadronic and leptonic decay branching fractions. A sequential charged heavy lepton with mass between 12.6 and 29.6 GeV/c2 and with massless neutrino is excluded at the 95% confidence level.

Results of a search for the pair production of charged heavy leptons in e+e− annihilations over the center-of-mass energy range of 50 to 60.8 GeV are reported. We assume that the leptons are of the sequential type but have allowed for the case where the associated neutrino might be massive. Separate searches for evidence for decays to hadronic and leptonic final states, searches specialized for the case where the charged lepton and its associated neutrino are close in mass, and a search for stable heavy leptons have uncovered no evidence for the production of such particles at these energies. Mass limits for heavy leptons and their associated neutrinos are determined for a range of hadronic and leptonic decay branching fractions. A sequential charged heavy lepton with mass between 12.6 and 29.6 GeV/c2 and with massless neutrino is excluded at the 95% confidence level.

We report on a search for the pair production of leptoquarks and colored leptons in e+e− annihilations t center-of-mass energies from 50 to 60.8 GeV, using the AMY detector at TRISTAN. No evidence for such particles is found and 95% CL mass limits are given.

We report results of a study of four-lepton final states produced in e+e− collisions at center-of-mass energies from 50 to 61.4 GeV using the AMY detector at the TRISTAN collider. For the cases where two or three charged tracks are produced at large angles relative to the beam direction, the cross sections agree with QED. However, we observe an excess of e+e−→e+e−μ+μ− events with four tracks at wide angles and with dimuon mass less than 1.0 GeV/c2.

We present the general properties of multihadron final states produced by e+e− annihilation at center-of-mass energies from 52 to 57 GeV in the AMY detector at the KEK collider TRISTAN. Global shape, inclusive charged-particle, and particle-flow distributions are presented. Our measurements are compared with QCD+fragmentation models that use either leading-logarithmic parton-shower evolution or QCD matrix elements at the parton level, and either string or cluster fragmentation for hadronization.Received 20 November 1989DOI:https://doi.org/10.1103/PhysRevD.41.2675©1990 American Physical Society

A search for the pair production of charged Higgs particles decaying via the H−→τν¯ mode has been made in e+e− annihilations at center-of-mass energies between 50 and 60.8 GeV using the AMY detector at the KEK collider TRISTAN. No evidence for their existence is observed and 95%-C.L. mass limits are presented. The result has been interpreted in terms of the tanβ parameter in the Higgs sector.Received 27 February 1990DOI:https://doi.org/10.1103/PhysRevD.42.949©1990 American Physical Society

Abstract Searches for the pair production of the supersymmetric partner particles of leptons, quarks, and non-minimal Higgs have been made in e + e − annihilations at center-of-mass energies between 50 and 60.8 GeV using the AMY detector at TRISTAN. No evidence for their existence is observed and 95% CL mass limits are presented.

QED processes up to O(α4) have been studied at center-of-mass energies between 50 and 57 GeV using the AMY detector at TRISTAN. A possible substructure of the electron and muon is investigated in terms of chiral invariant contact interactions and also in terms of excited lepton production. The differential cross section data for e+e−→e+e− are consistent with the standard model at a confidence level of only 3.5%. From the absence of excited lepton production, we establish new upper limits on the coupling to excited electrons of mass up to 56 GeV/c2 and on the coupling to excited muons of mass up to 52 GeV/c2.

A search for unstable heavy neutral leptons has been made at center-of-mass energies from 50 to 60.8 GeV with the AMY detector at the KEK Storage ring TRISTAN. The neutral leptons are assumed to decay via mixing to electrons and muons. Events with two leptons were searched for. No evidence for their existence was found. Limits in the mass range \ensuremath{\le}28.1 GeV/${c}^{2}$ and mixing-parameter range 9\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$\ensuremath{\le}\ensuremath{\Vert}${U}_{\mathrm{lL}}$${\ensuremath{\Vert}}^{2}$\ensuremath{\le}1 are presented for Dirac- and Majorana-type neutrinos.