CERN scientists capture anti-hydrogen atoms

As part of a major international experiment called ALPHA, based at CERN in Switzerland, researchers have helped to achieve trapping and holding atoms of ‘anti-hydrogen’, which has not been possible until now.

The project involves physicists at Swansea University led by Prof Mike Charlton, Dr Niels Madsen and Dr Dirk Peter van der Werf and Liverpool University under Prof Paul Nolan, all supported by the EPSRC.

This breakthrough will make it possible to study ‘anti-matter’ closely for the first time and so develop unprecedented insight into its composition and structure and improve understanding of the fundamental physical principles that underpin the Universe and the way it works.

For nearly a decade, scientists have been able to undertake the controlled production of anti-hydrogen atoms in the laboratory, a breakthrough that Swansea University contributed to.

But as anti-matter particles are instantly annihilated when they come into contact with matter, it has not, until now, been feasible to study anti-hydrogen atoms in any detail.

ALPHA has developed techniques that not only cool the anti-particles that make up anti-hydrogen and mix them to produce anti-hydrogen atoms, but also trap some anti-atoms long enough to be observed.

The key focus of this effort is said to have been the development of electromagnetic traps that have a number of cold species inside.

These traps don’t just provide the conditions needed to cool the anti-particles prior to mixing.

The cold anti-atoms formed also have a tiny magnetic moment (the product of a magnet’s pole strength and the distance between its poles), so they respond to magnetic fields.

By arranging the magnet coils in the right way, it is possible to set up a magnetic ‘well’ in the centre of the anti-particle mixing zone where anti-hydrogen has been trapped.

‘Every type of particle has its anti-matter equivalent, which is its mirror image in terms of having, for instance, the opposite electrical charge,’ said Charlton. ‘Because hydrogen is the simplest of all atoms, anti-hydrogen is the easiest type of anti-matter to produce in the laboratory. By studying it for the first time, we will be able to understand its properties and establish whether it really is the exact mirror image of hydrogen.

‘That understanding will hopefully enable us to shed light on exactly why almost everything in the known Universe consists of matter, rather than anti-matter, and what the implications are in terms of the fundamental way that the Universe functions.’

In order to detect the anti-hydrogen atoms, they were released from the trap. The silicon detector used to determine the positions of the resulting annihilations was developed and built at Liverpool. 

The initiative is expected to run for several years, with ALPHA commencing tests on anti-hydrogen atoms in around five years.