Trapped Anti-Hydrogen at CERN ALPHA

Antimatter you can study in the lab

First published: G. B. Andresen et al. (ALPHA), "Trapped antihydrogen", *Nature* 468 (2010): 673–676.

CERN traps 38 antihydrogen atoms for 172 milliseconds, opening direct precision tests of CPT symmetry and gravitational behaviour.

After decades of producing antiprotons and positrons separately, the ALPHA experiment at CERN combined them to form neutral antihydrogen atoms and trapped them magnetically — 38 atoms for 172 ms in the 2010 result, extended to ~1000 seconds by 2011. Subsequent work has measured the antihydrogen 1S-2S transition to a few parts in 10¹², matching ordinary hydrogen to that precision. The 2023 ALPHA-g experiment also reported antihydrogen falling under gravity exactly as ordinary matter does. The work is the first precision test of CPT symmetry in bound antimatter and provides empirical constraints on cosmological matter-antimatter asymmetry.