Is antimatter stable in a vacuum

Searching for new physics with rays of antimatter

Geneva (Switzerland) - Laser cannons, proton torpedoes and many other terrifying weapons are known from science fiction films and computer games. Antimatter rays are also very popular in space scenarios. Because when they hit normal matter, they immediately dissipate with it into large amounts of pure energy. Such exotic rays are currently still at the stage of pure basic research.

At Geneva’s CERN, too, it’s about the fundamental understanding of antimatter. As a research group now reports in the journal “Nature Communications”, they have succeeded in generating a beam of anti-atoms for the first time. However, these rays do not harbor any destructive powers. The handling of the volatile antimatter is so delicate that the scientists are already happy about a few anti-atoms that make it to the final measuring device. "We want to carry out high-precision investigations on this beam in order to find out more about the properties of the anti-atoms," says Naofumi Kuroda from the University of Tokyo, first author of the study. The researchers want to find out whether antimatter is really mirror-symmetrical to normal matter of which we and all other objects in the universe are made.

According to today's physics, antimatter is nothing more than a mirror image of ordinary matter. For every particle of normal matter there is exactly one antiparticle that has exactly the same mass and the opposite charge. The simplest atom, hydrogen, consists of a positively charged proton around which a negatively charged electron circles. The antiparticle of the proton is the antiproton, that of the electron is called the positron. Antihydrogen therefore consists of a negatively charged antiproton around which a positively charged positron circles. If one researches the properties of anti-hydrogen - for example its energy - and compares it with hydrogen, it is possible to determine very precisely whether matter and anti-matter differ in nuances. Hydrogen is particularly suitable for such experiments because it is the simplest atom and has been studied with unsurpassed precision. It compares perfectly with anti-hydrogen.

The problem with antimatter lies in this: On the one hand, today's theories predict that it should behave in a perfect mirror image of normal matter. On the other hand, there must be certain differences between the two forms of matter. Because the universe consists only of matter and not of antimatter. This means that the Big Bang must have produced a slightly larger amount of matter than antimatter. After a short time after all of the antimatter on matter was annihilated, only the matter that we are made of remained. One of the unsolved questions in physics is therefore: Why did more matter emerge than antimatter?

Another problem is based on so-called dark matter. Astrophysicists have discovered that a large part of the mass in the universe consists of completely unknown forms of matter and energy - there is no other way of explaining the accelerated expansion of space, for example. But there is no place for them in current theory. With the discovery of its last remaining particle, the Higgs boson, standard theory reached its brilliant conclusion in 2012. But it cannot explain everything, such as gravity. The theorists therefore now have a whole series of other theories in their drawer that go beyond this standard model. And in many of these theories there should be a minimal difference between matter and antimatter. The particle researchers therefore hope that precision measurements of antimatter will provide information on completely new physics.

Unfortunately, antimatter is difficult to make and also quite short-lived. Because even if it is basically just as stable as normal matter: Nowhere does a larger amount of antimatter survive for a long time. The scientists first have to create particles from antimatter in a particle accelerator and then use electromagnetic fields to skillfully lock them in so that the antimatter does not come into contact with normal matter. To do this, they need an extremely pure vacuum - because ordinary gas atoms also destroy each other with antimatter. However, there is no such thing as a perfect vacuum, so that atoms of antimatter continuously hit gas atoms in the apparatus and transform themselves into tiny flashes of radiation.

To produce anti-hydrogen, the researchers use antiprotons, such as those supplied by a pre-accelerator of the large LHC storage ring at CERN, as well as positrons that can be obtained from radioactive samples. Antiprotons and positrons then bring them to low speeds and lock them together in a magnetic trap, where both react to form anti-hydrogen. So far, scientists have been able to lock anti-hydrogen atoms in a magnetic trap for a certain period of time. However, the strong electromagnetic fields required for this impaired the spectroscopic measurements, which the researchers want to carry out with extraordinary precision.

That is why the CERN researchers are pursuing a different approach in the Asacusa experiment, which the Japanese scientists involved named after a famous temple in Tokyo: They use a complex sequence of magnets and electrodes to bundle the anti-hydrogen atoms into a beam on which they are attached then want to carry out high-precision measurements away from the interfering magnetic fields. With their apparatus, the researchers can now generate a beam that extends 2.7 meters and consists of around two dozen antiatoms per hour. Science fiction fans may be disappointed - this opens new doors for antimatter research.

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