Search for Heavy Neutral and Charged Leptons in e+ e- Annihilation at LEP

Abstract

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.

Figures (6)

• Figure 1: The distribution of the energy in a 30$^{\circ}$ cone around the second most energetic electron candidate. The points are the data, the solid histogram is the background Monte Carlo. The shaded histogram represents the simulated signal for e$^+$e$^- \rightarrow \mathrm{L^0}\overline{\mathrm{L^0}}$ for a sequential Dirac neutral lepton mass of 101 Ge V. Both histograms are normalized to the luminosity of the data. The arrow indicates the value of the applied cut; all other selection cuts are applied.
• Figure 2: The distribution of the sum of the muon energies, $E_{\mu 1}+E_{\mu 2}$, normalized to the beam enery. The points are the data, the solid histogram is the background Monte Carlo. The shaded histogram represents the simulated signal for e$^+$e$^- \rightarrow \mathrm{L^0}\overline{\mathrm{L^0}}$ for a sequential Dirac neutral lepton mass equal to 101 Ge V. Both histograms are normalized to the luminosity of the data. The arrow indicates the value of the applied cut; all other selection cuts are applied.
• Figure 3: The distribution of the cosine of the polar angle of the missing momentum, $\cos\theta_{miss}$. The points are the data, the solid histogram is the background Monte Carlo. The shaded histogram represents the simulated signal for e$^+$e$^- \rightarrow \mathrm{L^0}\overline{\mathrm{L^0}}$ for a sequential Dirac neutral lepton mass equal to 80 Ge V. The normalization for the signal Monte Carlo is scaled by a factor of 2 for better visibility. The arrows indicate the values of the applied cut.
• Figure 4: The distribution of a) the sum, $E_{jet_1} + E_{jet_2}$, of the energies of the hadronic jets normalized to the beam energy, b) the normalized visible energy in the event, c) the acollinearity angle of the two W candidates, d) the total transverse momentum, $p_t$. The points are the data, the solid histogram is the background Monte Carlo. The shaded histogram represents the simulated signal for e$^+$e$^- \rightarrow \mathrm{L^+} \mathrm{L^-}$ for a sequential charged lepton mass equal to 95 Ge V. The normalization for the signal Monte Carlo is scaled by a factor of 2 for better visibility. The arrows indicate the values of the applied cuts after all the other selection requirements.
• Figure 5: The two dimensional distribution of the ionization energy loss of the most energetic track, $dE/dx_1$, and the least energetic track, $dE/dx_2$. The solid circles represent the data and the open circles represent the simulated signal for e$^+$e$^- \rightarrow \mathrm{L^+} \mathrm{L^-}$ for a lepton mass of $0.985\times E_{beam}$. The signal normalization is arbitrary. The lines indicate the values of the applied cut.