Cited research Phys. Rev. Lett. 105, 013003 (2010)

A cloud of antiprotons has been cooled to the coldest temperature yet, paving the way for a fundamental test of the symmetry of matter and antimatter, say Jeffrey Hangst of Aarhus University in Denmark and his colleagues.

They cooled about 4,000 antiprotons to 9 kelvin using an evaporative technique previously used on neutral atoms. By 'tipping' an electromagnetic trap, the hottest antiprotons from an initial batch of 45,000 escaped, leaving behind the colder bunch. The team's next step will be to combine the cooled antiprotons with antielectrons and make a batch of anti-hydrogen atoms cold enough to be trapped and measured — to see if their properties mirror those of hydrogen.