Where has all the antimatter gone?

Researchers have claimed that a new study has brought us a step closer to understanding where all the antimatter has gone.

This matter-antimatter asymmetry is one of the greatest challenges in physics and at this moment in time the universe seems to be composed entirely of matter - the only antimatter around is created by us at places like CERN.

This new research, undertaken by the ALPHA experiment at CERN's Antiproton Decelerator (AD) in Geneva, is the first time that the electric charge of an anti-atom has been measured to high precision. Measuring the electric charge of antihydrogen atoms is a way to study any subtle differences between matter and antimatter which could account for the lack of antimatter in the universe.

The ALPHA experiment reports a measurement of the electric charge of antihydrogen atoms, finding it to be compatible with zero to eight decimal places.

This is the first time that the charge of an anti-atom has been measured to high precision and confirms our expectation that the charges of its constituents, the positron and antiproton, are equal and opposite.

Professor Mike Charlton, who leads the UK effort in ALPHA from Swansea University, said this advance was only possible using ALPHA's trapping technique, and we are optimistic that further developments of their programme will yield many such insights in the future.

To measure the charge of antihydrogen, the ALPHA experiment studied the trajectories of antihydrogen atoms released from the trap in the presence of an electric field. If the antihydrogen atoms had an electric charge, the field would deflect them, whereas neutral atoms would be undeflected. The result, based on 386 recorded events, gives a value of the antihydrogen electric charge as (-1.3 plus minus 1.1plus minus 0.4) x 10-8, the plus or minus numbers representing statistical and systematic uncertainties on the measurement.

With the restart of CERN's accelerator chain getting underway, the laboratory's antimatter research programme is set to resume soon.

The paper has been published in the journal Nature Communications.