Last year physicists working on the ALPHA experiment at the CERN particle-physics lab became the first to capture and store atoms of antimatter for long enough to examine it in detail. They trapped 38 antihydrogen atoms for about one fifth of a second. Now, the same team has posted a paper on the arXiv preprint server describing how it trapped 309 antihydrogen atoms for 1000 s. This boost in both number and trapping time should lead to important insights into the nature of antimatter.

Antihydrogen – the antimatter version of the hydrogen atom – is an atomic bound state of a positron and antiproton that was first produced at CERN towards the end of 1995. The study of antimatter is important in developing our understanding of the universe and in finding out why it contains so much more matter than antimatter.

With members from seven nations, the ALPHA team shared the Physics World 2010 Breakthrough of the Year award for its capture of antihydrogen. As well as extending the previous capture time by almost four orders of magnitude, the team has gained some interesting insights into the energy distribution of the captured anti-atoms.

Ground state first

The ALPHA team produced the antihydrogen by merging two clouds of cold plasmas: one containing positrons and the other antiprotons. By improving their trapping techniques, the researchers managed to hold the antihydrogen for more than 1000 s. These advances also meant that five times as many atoms were trapped per attempt. Calculations based on data from the experiment suggest that after about 0.5 s, most of the trapped antihydrogen atoms reach their lowest energy or ground state. As a result, the team says that its trapped sample is the first antihydrogen obtained in the ground state.

The researchers have also managed to make the first measurements of the energy distribution of the trapped anti-atoms. These data, along with computer simulations, should pave the way to a better understanding of trapping dynamics. The team carried out 40,000 simulated trapped antihydrogen events and compared them with the 309 experimental ones, to study the trapping and release processes.

Studying CPT violation

The ability to trap antihydrogen for long periods of time could lead to precision tests of charge–parity–time (CPT) violation, which could help explain why the universe contains so little antimatter. Other possible experiments include microwave spectroscopy of the antimatter and even laser and adiabatic cooling of antihydrogen to temperatures where gravitational effects are observable, according to the researchers.

The paper is currently under review for journal publication and therefore the ALPHA researchers were unable to comment further.

The research is described in arXiv:1104.4982.

For a detailed explanation about how the ALPHA experiment creates antimatter see "Antihydrogen trapped at CERN".