ATRAP – Antihydrogen TRAP

Peer inside atoms of antihydrogen

ATRAP is an experiment to compare hydrogen atoms with their antimatter equivalents – antihydrogen atoms. In 2002, ATRAP provided the first glimpse inside these antiatoms after researchers successfully created and measured a large number of them.

An atom of antihydrogen consists of an antiproton and a positron (an antielectron). One of the difficulties in making antimatter is the energy the antiprotons possess when they are first made, shooting out at close to the speed of light. The researchers needed to slow them down as much as possible and this meant cooling them. ATRAP was the first to use cold positrons to cool antiprotons. The two ingredients were confined in the same trap and when they had both reached a similar temperature, some combined to form atoms of antihydrogen (a positron orbiting an antiproton). This technique was developed from another experiment at CERN called TRAP, the predecessor of ATRAP.

The current experiment was set up in the late 1990s at the same time as the experiment called ATHENA. Both had the same goals and similar methods for producing the antihydrogen atoms, but they used different detection methods.

While the ATHENA experiment came to an end in 2004, ATRAP is still in operation. It continues with its goal creating antihydrogen cold enough and trapped for long enough for precise measurements to compare with ordinary hydrogen.