Scientists seek new means of studying anti-matter

Scientists are hoping to reveal some of the secrets of anti-matter by proposing a new way of cooling and studying it.

Researchers from the US and Canada have suggested a way of cooling trapped anti-hydrogen atoms to temperatures 25 times colder than already achieved, which would make them much more stable and easier to experiment on.

The proposed technique would involve hitting anti-hydrogen atoms with a laser in a way that would cause them to lose energy and cool down, provided sufficient light can be transmitted at the right frequency with the ultra-high vacuum equipment needed to make and trap anti-matter.

‘By reducing the anti-hydrogen energy, it should be possible to perform more precise measurements of all of its parameters,’ said Prof Francis Robicheaux of Auburn University in Alabama, co-author of a paper on the proposed method published today in the Institute of Physics’ Journal of Physics B.

‘Our proposed method could reduce the average energy of trapped anti-hydrogen by a factor of more than 10. The ultimate goal of anti-hydrogen experiments is to compare its properties to those of hydrogen. Colder anti-hydrogen will be an important step for achieving this.’

Anti-matter is composed of (anti-)particles that have the opposite charge and spin of the particles that make up the matter we see around us. So whereas a hydrogen atom is made from a proton and an electron, an anti-hydrogen atom is made from an anti-proton and an anti-electron or positron.

The idea of anti-matter was first proposed more than 100 years ago but because it is destroyed as soon as it comes into contact with matter it is very difficult to produce and to study.

It is only in the last three years that scientists have been able to study anti-hydrogen atoms and so far they have only been able to do so for a few minutes at a time. In 2011, researchers at CERN in Geneva were able to trap anti-hydrogen atoms for a record 1,000 seconds.

The new proposed method for cooling anti-hydrogen atoms uses an established way of cooling atoms known as Doppler cooling. The atoms absorb protons from a laser beam in such a way that they reduce the atoms’ momentum, slowing their vibrations and cooling them down.

However, because the techniques needed to trap anti-matter are so complex, it will be difficult to apply Doppler cooling to the anti-hydrogen atoms, said Robicheaux.

‘It is not trivial to make the necessary amount of laser light at a specific wavelength of 121nm. Even after making the light, it will be difficult to mesh it with an anti-hydrogen trapping experiment. By doing the calculations, we’ve shown that this effort is worthwhile.’

Through a series of computer simulations, the researchers have shown that anti-hydrogen atoms could be cooled to around 20 millikelvin — a much lower temperature than the 500 millikelvin achieved so far.

Although the processes that control the trapping are largely unknown, the researchers believe that laser cooling should increase the amount of time anti-hydrogen can be trapped for.

‘Whatever the processes are, having slower moving, and more deeply trapped, anti-hydrogen should decrease the loss rate,’ said Robicheaux.