1AKERS 1995R give the 95$\%$ CL limit $\sigma\mathrm {({{\mathit X}} {{\overline{\mathit X}}})}/\sigma\mathrm {({{\mathit \mu}} {{\mathit \mu}})}$ $<1.8 \times 10^{-4}$ for the pair production of singly- or doubly-charged stable particles. The limit applies for the mass range $40.4 - 45.6$ GeV for ${{\mathit X}^{\pm}}$ and $<45.6$ GeV for ${{\mathit X}^{\pm\pm}}$. See the paper for bounds for $\mathit Q$ = $\pm2$/3, $\pm4$/3.
References:
AKERS
1995R
ZPHY C67 203
Search for Heavy Charged Particles and for Particles with Anomalous Charge in ${{\mathit e}^{+}}$ ${{\mathit e}^{-}}$ Collisions at LEP
AKRAWY
1990O
PL B252 290
Search for Pair Produced Stable Singly-Charged Heavy Particles in ${{\mathit Z}^{0}}$ Decays