Optimizing Adiabatic Expansion Cooling to Improve Precision Measurements on Antihydrogen

As a test of the fundamental asymmetries between matter and antimatter, one can measure the electric charge of antihydrogen. In 2016, the ALPHA (Antihydrogen Laser PHysics Apparatus) experiment at CERN used stochastic acceleration (random electric kicks applied to putatively charged antiatoms) to place a limit on the charge of antihydrogen to about one part per billion [Ahmadi, M., Baquero-Ruiz, M., Bertsche, W. et al. An improved limit on the charge of antihydrogen from stochastic acceleration. Nature 529, 373–376 (2016)]. This measurement also set the best-known bounds on the positron charge. Here we use orbit simulations to investigate incorporating adiabatic expansion cooling into the measurement. We find that we can improve the limit on the charge of antihydrogen by a factor of one thousand and, to a lesser extent, improve the positron charge bound.