Search for Majoron at the COMET Experiment

A new Goldstone particle named Majoron is introduced in order to explain the origin of neutrino mass by some new physics models assuming that neutrinos are Majorana particle. By expanding signal region and using likelihood analysis, it becomes possible to search for Majoron at experiments that is originally designed to search for $\mu -e$ conversion. For the COMET experiment, the sensitivity of process $\mu \to eJ$ is able to reach $\mathcal{B}(\mu \to eJ)=2.3\times {10}^{-5}$ in Phase-I and $O({10}^{-8})$ in Phase-II. Meanwhile, the sensitivities to search for Majoron at future experiments are also discussed in this article.