We are developing a high brightness atomic Muonium (Mu = $\mu^+$$e^-$) beam, amenable to the direct measurement of the gravitational interaction of $\mu^+$. The characterization of this source and the prospective gravity experiment require background-free detection of atomic Mu emitted from the surface of T=200 mK superfluid helium (He-II). We developed the prototype of this detector based on the tracking of $\sim$50 MeV e$^+$ from $\mu^+$ decay and the simultaneous measurement of the liberated few-eV atomic e$^-$. The e$^+$ trackers consist of 16 scintillator bars, coupled to silicon photomultipliers (SiPM). The few-eV e$^-$ were first accelerated to $\sim$8 keV energies in an ion funnel, then left a few photon signal in a SiPM coupled to a scintillator pill. We present here the cryogenic development of SiPM detectors down to 170 mK for the first time, the temperature dependence of the single photon detection efficiency and the first test carried out using a surface muon beam at PSI.
|TIPP2020 abstract resubmission?||No, this is an entirely new submission.|