Searching for the dark sector in two-body antimuon decay with the polarization of monochromatic positrons

The mu(+) -> e+ X decay, where X is a dark sector boson, provides one of the strongest available bounds on the scale of dark sector interactions. The X boson can be an axion or a dark photon. We show that the concurrent determination of the antimuon and positron polarizations makes it possible to distinguish with a confidence level of 99% between the two dark sector portals with as few as 6 observed events in the case of the massless dark photon. Instead, the massive spin-1, dimension 4 dark portal cannot be distinguished from the axionlike case. We also discuss the possibility that the X boson be a massive spin-2 particle.

Automated summary

Research has shown that by simultaneously determining antimuon and positron polarizations, it is possible to distinguish between the axion and dark photon of the dark sector with a 99% confidence level with as few as 6 observed events. However, the massive spin-1 dark portal cannot be distinguished from the axionlike case, and the possibility of the X boson being a massive spin-2 particle is also discussed.