• Energy Research

A search for exotic unstable neutral and charged heavy leptons as well as for stable charged heavy leptons is performed with the L3 detector at LEP. Sequential, vector and mirror natures of heavy leptons are considered. No evidence for their existence is found and lower limits on their masses are set.

A search for exotic unstable neutral and charged heavy leptons as well as for stable charged heavy leptons is performed with the L3 detector at LEP. Sequential, vector and mirror natures of heavy leptons are considered. No evidence for their existence is found and lower limits on their masses are set.

We have studied the structure of hadronic events with a hard, %radiated isolated photon in the final state ($\mathrm{e^{+}e^{-}} \rightarrow$ Z $\rightarrow$ hadrons $+$ $\gamma$) in the 3.6 million hadronic data collected with the L3 detector at centre-of-mass energies around 91 GeV. The centre-of-mass energy of the hadronic system is in the range 30 GeV to 86 GeV. Event shape variables have been measured at these reduced centre-of-mass energies and have been compared with the predictions of different QCD Monte Carlo programs. The event shape variables and the energy dependence of their mean values are well reproduced by QCD models. We fit distributions of several global event shape variables to resummed $\cal{O} \alpha_{s}^{2})$ calculations to determine the strong coupling constant $\alpha_{s}$ over a wide range of energies. We find that the strong coupling constant $\alpha_{s}$ decreases with increasing energy, as expected from QCD.