These experiments assumed that a fourth generation ${{\mathit L}^{\pm}}$ decayed to a fourth generation ${{\mathit \nu}_{{L}}}$ (or ${{\mathit L}^{0}}$) where ${{\mathit \nu}_{{L}}}$ was stable, or that ${{\mathit L}^{\pm}}$ decays to a light ${{\mathit \nu}_{{{{\mathit \ell}}}}}$ via mixing.

See the “Quark and Lepton Compositeness, Searches for” Listings for limits on radiatively decaying excited leptons, $\mathit i.e.$ ${{\mathit \ell}^{*}}$ $\rightarrow$ ${{\mathit \ell}}{{\mathit \gamma}}$ . See the “WIMPs and other Particle Searches” section for heavy charged particle search limits in which the charged particle could be a lepton.

VALUE (GeV) CL% DOCUMENT ID TECN  COMMENT $\bf{>100.8}$ 95 ACHARD 2001 B L3 Decay to ${{\mathit \nu}}{{\mathit W}}$ $>101.9$ 95 ACHARD 2001 B L3 ${\mathit m}_{{{\mathit L}}}–{\mathit m}_{{{\mathit L}^{0}}}>15$ GeV • • We do not use the following data for averages, fits, limits, etc. • • $>81.5$ 95 ACKERSTAFF 1998 C OPAL Assumed ${\mathit m}_{{{\mathit L}^{\pm}}}–{\mathit m}_{{{\mathit L}^{0}}}>8.4$ GeV $>80.2$ 95 ACKERSTAFF 1998 C OPAL ${\mathit m}_{{{\mathit L}^{0}}}>{\mathit m}_{{{\mathit L}^{\pm}}}$ and ${{\mathit L}^{\pm}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit W}}$ $\text{<48 or >61}$ 95 1 ACCIARRI 1996 G L3 $>63.9$ 95 ALEXANDER 1996 P OPAL Decay to massless ${{\mathit \nu}}$'s $>63.5$ 95 BUSKULIC 1996 S ALEP ${\mathit m}_{{{\mathit L}}}–{\mathit m}_{{{\mathit L}^{0}}}$ $>7$ GeV $>65$ 95 BUSKULIC 1996 S ALEP Decay to massless ${{\mathit \nu}}$'s $\text{none 10 - 225}$ 2 AHMED 1994 CNTR H1 Collab. at HERA $\text{none 12.6 - 29.6}$ 95 KIM 1991 B AMY Massless ${{\mathit \nu}}$ assumed $>44.3$ 95 AKRAWY 1990 G OPAL $\text{none 0.5 - 10}$ 95 3 RILES 1990 MRK2 For (${\mathit m}_{{{\mathit L}^{0}}}-{\mathit m}_{{{\mathit L}^{0}}})>0.25 - 0.4$GeV $>8$ 4 STOKER 1989 MRK2 For (${\mathit m}_{{{\mathit L}^{+}}}–{\mathit m}_{{{\mathit L}^{0}}}$)= $0.4$ GeV $>12$ 4 STOKER 1989 MRK2 For ${\mathit m}_{{{\mathit L}^{0}}}=0.9$ GeV $\text{none 18.4 - 27.6}$ 95 5 ABE 1988 VNS $>25.5$ 95 6 ADACHI 1988 B TOPZ $\text{none 1.5 - 22.0}$ 95 BEHREND 1988 C CELL $>41$ 90 7 ALBAJAR 1987 B UA1 $>22.5$ 95 8 ADEVA 1985 MRKJ $>18.0$ 95 9 BARTEL 1983 JADE $\text{none 4-14.5}$ 95 10 BERGER 1981 B PLUT $>15.5$ 95 11 BRANDELIK 1981 TASS $>13.$ 12 AZIMOV 1980 $>16.$ 95 13 BARBER 1980 B CNTR $>0.490$ 14 ROTHE 1969 RVUE 1  ACCIARRI 1996G assumes LEP result that the associated neutral heavy lepton mass $>40$ GeV. 2  The AHMED 1994 limits are from a search for neutral and charged sequential heavy leptons at HERA via the decay channels ${{\mathit L}^{-}}$ $\rightarrow$ ${{\mathit e}}{{\mathit \gamma}}$ , ${{\mathit L}^{-}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit W}^{-}}$ , ${{\mathit L}^{-}}$ $\rightarrow$ ${{\mathit e}}{{\mathit Z}}$ ; and ${{\mathit L}^{0}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit \gamma}}$ , ${{\mathit L}^{0}}$ $\rightarrow$ ${{\mathit e}^{-}}{{\mathit W}^{+}}$ , ${{\mathit L}^{-}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit Z}}$ , where the ${{\mathit W}}$ decays to ${{\mathit \ell}}{{\mathit \nu}_{{{{\mathit \ell}}}}}$ , or to jets, and ${{\mathit Z}}$ decays to ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ or jets. 3  RILES 1990 limits were the result of a special analysis of the data in the case where the mass difference ${\mathit m}_{{{\mathit L}^{-}}}–{\mathit m}_{{{\mathit L}^{0}}}$ was allowed to be quite small, where ${{\mathit L}^{0}}$ denotes the neutrino into which the sequential charged lepton decays. With a slightly reduced ${\mathit m}_{{{\mathit L}^{\pm}}}$ range, the mass difference extends to about 4 GeV. 4  STOKER 1989 (Mark II at PEP) gives bounds on charged heavy lepton (${{\mathit L}^{+}}$) mass for the generalized case in which the corresponding neutral heavy lepton (${{\mathit L}^{0}}$) in the SU(2) doublet is not of negligible mass. 5  ABE 1988 search for ${{\mathit L}^{+}}$ and ${{\mathit L}^{-}}$ $\rightarrow$ hadrons looking for acoplanar jets. The bound is valid for ${\mathit m}_{{{\mathit \nu}}}$ $<$ 10 GeV. 6  ADACHI 1988B search for hadronic decays giving acoplanar events with large missing energy. E$_{{\mathrm {cm}}}{}^{ }$ = 52 GeV. 7  Assumes associated neutrino is approximately massless. 8  ADEVA 1985 analyze one-isolated-muon data and sensitive to ${{\mathit \tau}}$ $<$10 nanosec. Assume B(lepton) = 0.30. $\mathit E_{{\mathrm {cm}}}$ = 40$-$47 GeV. 9  BARTEL 1983 limit is from PETRA ${{\mathit e}^{+}}{{\mathit e}^{-}}$ experiment with average $\mathit E_{{\mathrm {cm}}}$ = 34.2 GeV. 10  BERGER 1981B is DESY DORIS and PETRA experiment. Looking for ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit L}^{+}}{{\mathit L}^{-}}$ . 11  BRANDELIK 1981 is DESY-PETRA experiment. Looking for ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit L}^{+}}{{\mathit L}^{-}}$ . 12  AZIMOV 1980 estimated probabilities for ${{\mathit M}}$ + ${{\mathit N}}$ type events in ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit L}^{+}}{{\mathit L}^{-}}$ deducing semi-hadronic decay multiplicities of ${{\mathit L}}$ from ${{\mathit e}^{+}}{{\mathit e}^{-}}$ annihilation data at $\mathit E_{{\mathrm {cm}}}$ = (2/3)${}{\mathit m}_{{{\mathit L}}}$. Obtained above limit comparing these with ${{\mathit e}^{+}}{{\mathit e}^{-}}$ data (BRANDELIK 1980 ). 13  BARBER 1980B looked for ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit L}^{+}}{{\mathit L}^{-}}$ , ${{\mathit L}}$ $\rightarrow$ ${{\mathit \nu}_{{L}}^{+}}$ X with MARK-J at DESY-PETRA. 14  ROTHE 1969 examines previous data on ${{\mathit \mu}}$ pair production and ${{\mathit \pi}}$ and ${{\mathit K}}$ decays.

References:

ACHARD 2001B PL B517 75 Search for Heavy Neutral and Charged Leptons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at LEP ACKERSTAFF 1998C EPJ C1 45 Search for Unstable Heavy and Excited Leptons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions at $\sqrt {s }$ = $170 - 172$ GeV ACCIARRI 1996G PL B377 304 Search for Unstable Sequential Neutral and Charged Heavy Leptons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at $\sqrt {s }$ = 130 and 136 GeV ALEXANDER 1996P PL B385 433 Search for Unstable Neutral and Charged Heavy Leptons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions at $\sqrt {s }$ = 130 and 136 GeV BUSKULIC 1996S PL B384 439 Search for Heavy Lepton Pair Production in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions at the Centre-of-Mass Energies of 130 and 136 GeV AHMED 1994 PL B340 205 A Search for Heavy Leptons at HERA KIM 1991B IJMP A6 2583 Searches for Charged Heavy Leptons with Arbitrary Neutrino Masses in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilations at $\sqrt {s }$ = 50-60.8 GeV AKRAWY 1990G PL B240 250 A Direct Search for New Charged Heavy Leptons at LEP RILES 1990 PR D42 1 Search for a Nearly Degenerate Lepton Doublet (${{\mathit \ell}^{-}}$, heavy-lepton${}^{0}$) STOKER 1989 PR D39 1811 Limits on New Lepton Pairs (${{\mathit \ell}^{-}}$, heavy-lepton${}^{0}$) with Arbitrary Neutrino Mass ABE 1988 PRL 61 915 Search for New Charged Leptons Decaying into Massive Neutrinos and Stable Charged Leptons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions ADACHI 1988B PR D37 1339 Search for Sequential Heavy Leptons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions at $\sqrt {s }$ = 52 GeV BEHREND 1988C ZPHY C41 7 A Search for New Leptons ALBAJAR 1987B PL B185 241 Events with Large Missing Transverse Energy at the CERN Collider: Search for the Decays of ${{\mathit W}^{\pm}}$ into Heavy Leptons and ${{\mathit Z}^{0}}$ into Noninteracting Particles. Paper 2 ADEVA 1985 PL 152B 439 New Particles Searches Also PRPL 109 131 A Summary of Experimental Results from MARK-J: High Energy ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions at PETRA BARTEL 1983 PL 123B 353 A Search for New Heavy Leptons at PETRA BERGER 1981B PL 99B 489 Lepton Pair Production and Search for a New Heavy Lepton in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation BRANDELIK 1981 PL 99B 163 Search for New Sequential Leptons in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Annihilation at PETRA Energies AZIMOV 1980 JETPL 32 664 Predicted Properties of a Superheavy Lepton BARBER 1980B PRL 45 1904 Experimental Study of Heavy Charged Leptons and Search for Scalar Partners of Muons at PETRA (12 GeV ${}\leq{}$ $\mathit E_{{\mathrm {cm}}}{}\leq{}$ 36.7 GeV) ROTHE 1969 NP B10 241 Are There Heavy Leptons?