Astroparticle Physics with a Trapped Electron

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No one knows what 84% of the matter in the universe is, and the goal of APTE is tofind out. APTE will investigate two leading types of dark matter: axions and millichargedparticles. Axions not only resolve a longstanding puzzle in particle physics, but if theirmass is 0.001-1 meV they are an excellent dark matter candidate. Millicharged particlesarise in some theories beyond the Standard Model and have recently been suggested as a com-ponent of dark matter that could explain the anomalous cooling of hydrogen in the early universe.APTE will use an electron in a cryogenic Penning trap in an entirely new application: aquantum sensor for astroparticle physics. The radial modes of the trapped electron will bemonitored for transitions caused by collisions with millicharged dark matter or the absorptionof single microwave photons from axion decays. Changes in radial quantum state will beimprinted onto the trapped electron's axial frequency using a strong magnetic inhomogeneity,the same principle as used to measure the electron magnetic moment. Drawing on myexperience in BASE, one of the world's most sensitive cryogenic Penning traps, I will pioneerthe use of advanced phase sensitive measurement protocols of my own invention. These willbe used to monitor the electron's axial frequency for phase jumps which occur when the radialmode changes. With this electron single photon counter we will be able to overcome the Stan-dard Quantum Limit which severely degrades our ability to investigate axion masses > 0.04 meV.APTE will perform a first search for dark matter axions with masses around 0.128 meVand millicharged dark matter particles with masses up to at least 1 GeV and charges 10^-1 to 10^-7 e. Both measurements probe important theories in a regime where there is currently nodata and few proposed experiments. This ground-breaking project will lay the foundations fora future program of axion searches, as well as other applications in fundamental physics.