Lepton Symmetry Experiment – matter / antimatter symmetry test with electron and positron

ongoing

In modern physics we are faced with the unsatisfactory situation that the Standard Model (SM), which condenses our current state of knowledge in the form of quantum field theories, despite its spectacular success in the prediction of laboratory results, fails in explaining even the most basic properties of our Universe, such as the disparity of matter and antimatter and the possible existence of dark matter. In the quest to search for answers to these questions, low energy, high precision experiments in ion traps have taken a pivotal role by allowing precise tests of the charge, parity and time (CPT) reversal symmetry. I propose an ambitious, next-generation Penning-trap experiment that will enable us to directly compare the magnetic moments of electron and positron at 14 digits precision. To this end, we will simultaneously trap a single positron and an electron in the same trap and directly compare their spin precession frequencies. To enable the co-trapping of the oppositely charged particle and antiparticle, we will bind the electron in a hydrogenlike 4He+ ion. As a result of the binding, the spins of both particles show a slow beat, which can be accurately measured. Any deviation of this beat frequency from the prediction by quantum electrodynamics (QED) reveals a CPT violation. This way, LSYM will enable a uniquely sensitive comparison of particle and antiparticle charge, mass and g-factors and thus yield the most stringent CPT test in the lepton sector. To this end, we will develop a novel, superconducting Penning trap apparatus, which can be cooled to millikelvin temperatures to largely eliminate black-body radiation. Building upon techniques recently pioneered by my group, LSYM will allow the coherent “quantum” measurement of the difference of the spin precession frequencies. Furthermore, with this toolbox at hand, we will have access to a new class of intriguing measurements, such as an order of magnitude improved determination of the electron atomic mass.