Measurement of the Absolute Branching Fraction for   $\Lambda_c^+\rightarrow \Lambda \mu^+\nu_{\mu}$
  We report the first measurement of the absolute branching fraction for $\Lambda^+_{c}\rightarrow \Lambda \mu^+\nu_{\mu}$. This measurement is based on a sample of $e^+e^-$ annihilation data at a center-of-mass energy of $\sqrt{s}=4.6$ GeV collected with the BESIII detector at the BEPCII storage rings. The sample corresponds to an integrated luminosity of 567 pb$^{-1}$. The branching fraction is determined to be $\mathcal B({\Lambda^+_c\rightarrow \Lambda \mu^+\nu_{\mu}})=(3.49\pm0.46({\rm stat})\pm0.27({\rm syst}))\%$. In addition, we calculate the ratio $\mathcal{B}(\Lambda^+_c\rightarrow \Lambda \mu^+\nu_{\mu})/\mathcal{B}(\Lambda^+_c\rightarrow \Lambda e^+\nu_{e})$ to be $0.96\pm0.16({\rm stat})\pm0.04({\rm syst})$. 
M. Ablikim, M. N. Achasov, S. Ahmed, X. C. Ai, O. Albayrak, M.   Albrecht, D. J. Ambrose, A. Amoroso, F. F. An, Q. An, J. Z....
hep-ex