Tests of fundamental symmetries using antihydrogen: the ALPHA experiment at CERN

by Prof. Jeffrey Scott Hangst (Aarhus University (DK))

Monday 24 Nov 2025, 11:00 → 12:00 Europe/Zurich

BSP 626 (EPFL)

The ALPHA experiment at CERN is unique in its demonstrated ability to study the physical properties of antihydrogen – the antimatter equivalent of the simplest atom. Such studies are motivated by the apparent absence of antimatter in the observable universe, and they probe the fundamental symmetries that underlie current theory. For example, the Standard Model requires that hydrogen and antihydrogen have the same spectrum. The possibility of applying the precision measurement and manipulation techniques of atomic physics to an antimatter atom makes antihydrogen a very compelling testbed for symmetries such as CPT and the Weak Equivalence Principle of General Relativity. To study antihydrogen, it must first be produced, trapped, and then held for long enough to make a measurement – typically using very few anti-atoms. I will discuss the latest developments in antihydrogen physics, including the state-of-the art of spectroscopic and gravitational studies using the ALPHA-2 and ALPHA-g machines. ALPHA-g is designed to measure the direction and magnitude of the gravitational acceleration of antimatter in the field of the Earth1. In ALPHA-2, we have studied several laser and microwave driven transitions and demonstrated laser cooling of trapped antihydrogen2. Very recently, we have shown that it is possible to accumulate more than 104 anti-atoms in a single day. I will illustrate the techniques necessary to achieve these many milestones and consider the future of antihydrogen studies.

 

1. Observation of the effect of gravity on the motion of antimatter (ALPHA Collaboration) Nature 621,716–722 (2023).

2. Laser cooling of antihydrogen atoms (ALPHA Collaboration) Nature 592, 35–42 (2021).