Measurement of the $B_c^+$ meson lifetime using $B_c^+ \to   J\!/\!\psi\mu^+ \nu_{\mu} X$ decays
  The lifetime of the $B_c^+$ meson is measured using semileptonic decays having a $J\!/\!\psi$ meson and a muon in the final state. The data, corresponding to an integrated luminosity of $2\mathrm{~fb^{-1}}$, are collected by the LHCb detector in $pp$ collisions at a centre-of-mass energy of $8\,\mathrm{TeV}$. The measured lifetime is $$\tau = 509 \pm 8 \pm 12 \mathrm{~fs},$$ where the first uncertainty is statistical and the second is systematic. 
LHCb collaboration: R. Aaij, B. Adeva, M. Adinolfi, A. Affolder, Z.   Ajaltouni, J. Albrecht, F. Alessio, M. Alexander, S. A...
hep-ex