These limits are obtained from ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \nu}^{*}}{{\mathit \nu}^{*}}$ and thus rely only on the (electroweak) charge of ${{\mathit \nu}^{*}}$. Form factor effects are ignored unless noted. The ${{\mathit \nu}^{*}}$ coupling is assumed to be of sequential type unless otherwise noted. All limits assume a dominant ${{\mathit \nu}^{*}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit \gamma}}$ decay except the limits from $\Gamma\mathrm {({{\mathit Z}})}$.

VALUE (GeV) CL% DOCUMENT ID TECN  COMMENT $\bf{> 1600}$ 95 1 AAD 2015 AP ATLS ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit \nu}^{*}}{{\mathit \nu}^{*}}{{\mathit X}}$ • • We do not use the following data for averages, fits, limits, etc. • • 2 ABBIENDI 2004 N OPAL $>102.6$ 95 3 ACHARD 2003 B L3 ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \nu}^{*}}{{\mathit \nu}^{*}}$ Homodoublet type 1  AAD 2015AP search for ${{\mathit \nu}^{*}}$ pair production in evens with three or more charged leptons in ${{\mathit p}}{{\mathit p}}$ collisions at $\sqrt {s }$ = 8 TeV. The quoted limit assumes ${{\mathit \Lambda}}$ = ${\mathit m}_{{{\mathit \nu}^{*}}}$, ${{\mathit f}}$ = ${{\mathit f}^{\,'}}$ = 1. The contact interaction is included in the ${{\mathit \nu}^{*}}$ production and decay amplitudes. 2  From ${{\mathit e}^{+}}{{\mathit e}^{-}}$ collisions at $\sqrt {s }$ = $192 - 209$ GeV, ABBIENDI 2004N obtain limit on ${\mathit \sigma (}$ ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ $\rightarrow$ ${{\mathit \nu}^{*}}{{\mathit \nu}^{*}}{)}$ B${}^{2}$( ${{\mathit \nu}^{*}}$ $\rightarrow$ ${{\mathit \nu}}{{\mathit \gamma}}$ ). See their Fig.2. The limit ranges from 20 to 45 fb for ${\mathit m}_{{{\mathit \nu}^{*}}}$ $>$ 45 GeV. 3  From ${{\mathit e}^{+}}{{\mathit e}^{-}}$ collisions at $\sqrt {\mathit s }$ = $189 - 209$ GeV. ${{\mathit f}}$ = $\text{-}{{\mathit f}^{\,'}}$ is assumed. ACHARD 2003B also obtain limit for ${{\mathit f}}$ = ${{\mathit f}^{\,'}}$: ${\mathit m}_{{{\mathit \nu}_{{e}}^{*}}}>101.7$ GeV, ${\mathit m}_{{{\mathit \nu}_{{\mu}}^{*}}}>101.8$ GeV, and ${\mathit m}_{{{\mathit \nu}_{{\tau}}^{*}}}>92.9$ GeV. See their Fig.$~$4 for the exclusion plot in the mass-coupling plane.

References:

AAD 2015AP JHEP 1508 138 Search for New Phenomena in Events with Three or More Charged Leptons in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 8 TeV with the ATLAS Detector ABBIENDI 2004N PL B602 167 Multiphoton Events with Large Missing Energy in ${{\mathit e}^{+}}{{\mathit e}^{-}}$ Collisions at $\sqrt {s }$ = $192 - 209$ GeV ACHARD 2003B PL B568 23 Search for Excited Leptons at LEP