Cern physicists trap antimatter for 16 minutes

Scientists at the European particle physics lab will use trapping techniques to study the structure of anti-hydrogen, and the effects of gravity on antimatter
Written by Tom Espiner, Contributor

Physicists at Cern have trapped a quantity of antimatter atoms for 1,000 seconds, a breakthrough that should allow them to better study the vulnerable particles.

Alpha experiment Cern

Physicists at Cern working on the Alpha experiment have trapped antimatter atoms for 1,000 seconds, or 16 minutes. Photo credit: Cern

Scientists at Cern's Alpha experiment can now start to study anti-hydrogen atoms in greater depth, Alpha experiment spokesman Jeffrey Hangst told ZDNet UK on Monday, following  the publication on Sunday of a paper from Alpha experiment physicists in Nature Physics, outlining how they traped antimatter for 16 minutes.

"We can now start to measure the structure of anti-hydrogen," said Hangst. "We can do a measurement now even with a few atoms."

Alpha experiment physicists have captured a total of 300 atoms, one at a time, and are working hard to increase the rate of capture, said Hangst. The experiment mixes positrons — the antimatter equivalent of electrons — with anti-protons from Cern's Antiproton Decelerator to create the anti-hydrogen.

When first created, anti-hydrogen atoms are unstable due to their high-energy state, and would be annihilated if they came into contact with ordinary matter, said Hangst. Physicists get round the the initial high instability by capturing the antimatter atoms in a vacuum.

The antimatter is held in an electromagnetic field by superconducting magnets and cooled to a maximum temperature of 0.5° above absolute zero. This puts the anti-hydrogen in its ground state, the minimal energy configuration for any atom. This increases the stability of the particle by bringing the orbit of the anti-electron closer to the anti-proton, said Hangst.

Microwave experiment

In the short term, physicists hope to perform a number of experiments. One experiment, which Hangst described as "simple and elegant", involves shining microwaves at the right frequency to flip the antimatter from one magnetic polarity to another.

This will be a resonant interaction. If we can deliver that, we will have done the first internal probe of antimatter.
– Jeffrey Hangst

"This will be a resonant interaction," said Hangst. "If we can deliver that, we will have done the first internal probe of antimatter."

The anti-hydrogen atom, when hit with the right microwave frequency, will escape the trap. Physicists can then detect when the antimatter is annihilated, and draw conclusions about its structure.

The experiment will test if anti-hydrogen behaves in the same way as hydrogen, which a group of theories about how the universe works called the Standard Model predicts should happen.

"If there's a difference [in behaviour], then something has been overlooked in the Standard Model," said Hangst. Moreover, capturing and holding antimatter for 16 minutes will allow physicists in the long term to study the effects of gravity on anti-hydrogen, he said.

CPT symmetry

In addition, allowing the particles to relax into a ground state will allow physicists to study CPT (charge, parity, time) symmetry. CPT symmetry thought experiments involve: swapping the charges of particles; swapping the parity, which is like looking at the the particle in a three-dimensional mirror; and reversing the flow of time.

Although a highly successful and productive model, CPT symmetry cannot explain why the observed universe is almost entirely matter. The theory says instead that roughly equal amounts of matter and antimatter should have been created at the Big Bang, a starting state that could not have evolved to today's universe under our current understanding of physics.

Scientists at Cern announced in November that they had managed to trap antimatter.

The Cern Alpha antimatter experiment is running at the same time as a space-based experiment called the Alpha Magnetic Spectrometer (AMS), aboard the International Space Station. The two experiments, which are not directly related, are looking at different aspects of antimatter.

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