Measurement of the lifetime of the $B_c^+$ meson using the $B_c^+rightarrow J/psipi^+$ decay mode

The difference in total widths between the $B_c^+$ and $B^+$ mesons is measured using 3.0fb$^{-1}$ of data collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the LHC. Through the study of the time evolution of $B_c^+ rightarrow J/psi pi^+$ and $B^+rightarrow J/psi K^+$ decays, the width difference is measured to be $$ DeltaGamma equiv Gamma_{B_c^+} - Gamma_{B^+} = 4.46 pm 0.14 pm 0.07mm^{-1}c,$$ where the first uncertainty is statistical and the second systematic. The known lifetime of the $B^+$ meson is used to convert this to a precise measurement of the $B_c^+$ lifetime, $$tau_{B_c^+} = 513.4 pm 11.0 pm 5.7fs,$$ where the first uncertainty is statistical and the second systematic.