We have measured the branching ratio of the three-body process in the nonmesonic weak decay of ${}_{\Lambda }{}^{12}\mathrm{C}$ to be $0.29\pm 0.13$. This result was obtained by reproducing the nucleon and the nucleon pair yields introducing a measured final state interaction. At the same time, we have determined the absolute decay widths, ${\Gamma }_n$ and ${\Gamma }_p$, along with ${\Gamma }_{2N}$, whose relative ratio has been a long-standing puzzle. Including the three-body process, we have successfully reproduced the nucleon energy distribution, the coincidence two-nucleon angular correlation, and the momentum sum distribution simultaneously.

• Received 5 August 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.182502