Search for a Non-Relativistic Boson in Two-Body Antimuon Decay

Abstract

We demonstrate the feasibility of probing the charged lepton flavor violating decay ${\mu }^{+}\to e^{+}{X}^0$ for the presence of a slow-moving neutral boson $X^0$ capable of undergoing gravitational binding to large structures, and as such able to participate in some cosmological scenarios. A short exposure to surface antimuons from beamline M20 at TRIUMF generates a branching ratio limit of $\lesssim 10^{-5}$. This is comparable or better than previous searches for this channel, although in a thus-far unexplored region of $X^0$ phase space very close to the kinematic limit of the decay. The future improved sensitivity of the method using a customized p-type point contact germanium detector is described.

arXiv comment5 pages, 5 figures. V.2 includes a comparison with future sensitivity of Mu3e in final figure

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