A method to measure the absolute branching fractions of $\Lambda_c$ decays

It is proposed to exploit the decay of the meson ${B}^+ \rightarrow p \pi^+ \pi^+ \bar{\Sigma}_c^{--}$ and of its charge conjugate $B^-$ copiously produced at LHC to obtain a sample of $\Lambda_c$ baryons through the strong decay $\Sigma_c \rightarrow \Lambda_c \pi$. The sample thus obtained is not affected by biases typically introduced by selections that depend on specific decay modes. Therefore it allows a measurement of the absolute branching fraction for the decay of the $\Lambda_c$ baryon into $ p K \pi$ or into other observable final states to be performed in a model independent manner. The accuracy that can be achieved with this method is discussed and it is shown that it would be either competitive with or an improvement over current measurements.