Particle Physics: Measuring the charge of antimatter

The most precise constraint on the charge of the antihydrogen atom, to date, is presented by the ALPHA Collaboration at CERN in this week’s Nature Communications. The finding puts a new limit on any potential differences between matter and antimatter.

Our present theoretical understanding of the nature of matter and antimatter is that they should behave in similar ways; any difference, no matter how small, would alter the physical models we have. However, the absence of antimatter in any appreciable scale in the universe makes experimental tests of this very difficult. Efforts are underway to produce antimatter and store it in sufficient volumes to enable such tests, though only very small volumes can currently be produced.

The ALPHA Collaboration at CERN has performed a retrospective analysis of their recent experimental efforts to trap and study antihydrogen atoms, looking for any deviation from the expected neutral charge (which has already been obtained to high precision for ordinary hydrogen). This analysis consisted of looking for any deflection of antihydrogen atoms by electric fields in the apparatus, which would signal that they have a net charge.

From their data, combined with thorough numerical modelling, they found that antihydrogen is charge neutral to (-1.3 ± 1.1 ± 0.4) × 10-8 times the fundamental electric charge. This measurement is around one million times more precise than previous estimates and allows researchers to rule out some effects in related measurements of the acceleration of antihydrogen under gravity.