Antimatter at CERN

The first atoms of antihydrogen – the antimatter counterpart of the simplest atom, hydrogen – were created at CERN in 1995. An atom of antihydrogen consists of an antiproton and a positron (an antielectron), which makes it the simplest antiatom. Unfortunately, this does not make it any easier to produce in the lab. It was a difficult task both for the physicists and for the operation team at CERN’s Low Energy Antiproton Ring (LEAR) – where the discovery of antihydrogen took place. The researchers allowed antiprotons circulating inside LEAR to collide with atoms of a heavy element. Any antiprotons passing close enough to heavy atomic nuclei could create an electron-positron pair; in a tiny fraction of cases, the antiproton would bind with the positron to make an atom of antihydrogen.

However, the fleeting existence of the antiatoms meant that they could not be used for further studies. Each one existed for only about 40 billionths of a second, travelling at nearly the speed of light over a path of 10 metres before it annihilated with ordinary matter. In 2011, ALPHA – an international collaboration currently running experiments at CERN's Antiproton Decelerator facility – succeeded in trapping antihydrogen atoms for 1000 seconds. By precise comparisons of hydrogen and antihydrogen, several experimental groups hope to study the properties of antihydrogen and see if it has the same spectral lines as hydrogen. One group, AEGIS, will even attempt to measure g, the gravitational acceleration constant, as experienced by antihydrogen atoms.

The ACE experiment is testing the use of antiprotons for cancer therapy. From 2016, a facility called ELENA will enable all experiments working at the Antiproton Decelerator to get lower energy and more abundant antiproton beams, making it even easier to produce antihydrogen in large quantities.

Voir en français

Featured updates on this topic

21 Jan 2016 – ALPHA shows the most accurate measurement yet of the electric charge of antihydrogen atoms in a new Nature paper


4 Apr 2018 – The ALPHA experiment at CERN has measured a light-induced transition in antihydrogen with unprecedented precision

7 Mar 2018 – A project called PUMA aims to transport antimatter from one CERN facility to another in order to investigate exotic nuclear phenomena

19 Oct 2017 – The BASE collaboration breaks its own precision measurement record of antiproton’s magnetic moment

24 Aug 2017 – GBAR (Gravitational Behaviour of Antihydrogen at Rest) has just had a brand new part installed – an antiproton decelerator

4 Aug 2017 – The first antiproton beam has been successfully injected and circulated into ELENA, the Extra Low ENergy Antiproton deceleration ring

3 Aug 2017 – The ALPHA experiment at CERN’s Antiproton Decelerator reports the first observation of the hyperfine structure of antihydrogen

17 Mar 2017 – What is the effect of gravity on antimatter? A new experiment at CERN is preparing to join the quest to find the answer to this question in physics

18 Jan 2017 – CERN experiment reports sixfold improved measurement of the magnetic moment of the antiproton

20 Dec 2016 – BASE has kept a shot of antiprotons trapped for more than one year: it is the longest-lived, coldest, known baryonic antimatter object in the Universe

28 Nov 2016 – The commissioning of ELENA, a new antiproton deceleration ring, has begun