jeudi 24 septembre 2015

Antihydrogen at CERN: 20 years and going strong

CERN - European Organization for Nuclear Research logo.

Sept. 24, 2015

Twenty years ago a team of scientists at CERN led by Walter Oelert succeeded in producing the first atoms made of antimatter particles.

The nine atoms of antihydrogen – the antimatter counterpart of the simplest atom, hydrogen – were made at CERN’s Low Energy Antiproton Ring (LEAR) facility. This world premiere happened exactly 30 years after the discovery of the antiproton and opened a new chapter in the study of antimatter.

Low Energy Antiproton Ring (LEAR) facility. Image Credit: CERN

Comparisons of hydrogen and antihydrogen atoms constitute one of the best ways to make precise tests of differences between matter and antimatter. Their spectra are predicted to be identical, so any tiny differences would open a window to new physics, and could help in solving the antimatter mystery.

The atoms produced in 1995 remained in existence for about 40 billionths of a second, travelling for 10 metres at nearly the speed of light before being annihilated by ordinary matter and producing the signal that showed the anti-atoms had been formed.

Seven years later, CERN's Antiproton Decelerator (AD) made headlines around the world when the ATHENA and ATRAP experiments successfully produced large numbers of antihydrogen atoms for the first time.

Image above: The ALPHA experiment, one of five experiments that are studying antimatter at CERN (Image: Maximilien Brice/CERN).

Today, the AD serves five experiments that are studying antimatter in different ways: AEgIS, ALPHA, ASACUSA, ATRAP and BASE.

ALPHA – ATHENA’s successor – is specifically designed to trap antihydrogen particles for longer than its predecessors, so they can be studied in finer detail than ever before. The ALPHA collaboration has already measured the electric charge of an antiatom to a much higher precision than before. The ASACUSA collaboration, which also has high-precision studies of antihydrogen in its sights, has demonstrated the first-ever production of a beam of antiatoms.

Earlier this year further advances were made when the Baryon Antibaryon Symmetry Experiment (BASE) reported the most precise comparison of the charge-to-mass ratio of the proton to that of its antimatter equivalent, the antiproton. The study, which took 13,000 measurements over a 35-day period, showed that protons and antiprotons have identical mass-to-charge ratios.

The AEgIS experiment, which has just started operation this year, is designed specifically to measure the gravitational interaction of antimatter. Another, future experiment, GBAR, will make similar investigations.

These recent successes mark a growth in antimatter research that CERN’s AD can no longer keep up with, as more and more low-energy antiprotons are needed for experiments. An upgrade to the AD, called ELENA, will become operational in 2017. This is where GBAR will be installed.

ELENA will decelerate the antiprotons from the AD still further, allowing many more to be trapped by the experiments. With the additional ability to serve four experiments almost simultaneously, ELENA will usher in a new era in the investigation of the relationship between matter and antimatter in the universe.

For more read: "In the steps of the antiproton":


CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 22 Member States.

Related links:

CERN's Antiproton Decelerator (AD):

ATRAP experiment:

ALPHA experiment:

ELENA experiment:

Related article:

BASE compares protons to antiprotons with high precision:

For more information about the European Organization for Nuclear Research (CERN), visit:

Images (mentioned), Text, Credits: CERN/Harriet Jarlett.

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