The ASACUSA experiment at CERN has taken an important step forward in developing an innovative technique for studying antimatter. Using a novel particle trap, called a CUSP trap, the experiment has succeeded in producing significant numbers of antihydrogen atoms in flight.
Antimatter – or the lack of it – remains one of the biggest mysteries of science. Matter and its counterpart are identical except for opposite charge, and they annihilate when they meet. At the Big Bang, matter and antimatter should have been produced in equal amounts. However, we know that our world is made up of matter: antimatter seems to have disappeared. To find out what has happened to it, scientists employ a range of methods to investigate whether a tiny difference in the properties of matter and antimatter could point towards an explanation.
One of these methods is to take one of the best-known systems in physics, the hydrogen atom, which is made of one proton and one electron, and check whether its antimatter counterpart, antihydrogen, consisting of an antiproton and a positron, behaves in the same way. The challenge is to create antihydrogen atoms, and keep them away from ordinary matter for long enough to study them. ASACUSA’s CUSP trap uses a combination of magnetic fields to bring antiprotons and positrons together to form antihydrogen atoms, and then channel them along a vacuum pipe where they can be studied in flight. So far, only a few antihydrogen atoms have been produced in this way, but the experiment’s ultimate goal is to produce enough to investigate their behaviour in detail with the help of microwaves.
ASACUSA’s approach is complementary to that of the ALPHA experiment, which reported new results on 17 November. The procedures used to form antihydrogen build on techniques developed by a third antihydrogen experiment at CERN, ATRAP, which pioneered trapping techniques in the 1990s, and is also working on trapping antihydrogen.
“With these alternative methods of producing and eventually studying antihydrogen, antimatter will not be able to hide its properties from us much longer,” said Yasunori Yamazaki of Japan’s RIKEN research centre and a team leader of the ASACUSA collaboration. “There’s still some way to go, but we’re very happy to see how well this technique works.”
CERN is the only laboratory in the world that operates a dedicated low-energy antiproton facility. As far back as 1995, the first nine atoms of antihydrogen were produced at CERN. Then, in 2002, the ATHENA and ATRAP experiments showed that it was possible to produce antihydrogen in large quantities, opening up the possibility of conducting detailed studies. Today, CERN’s antihydrogen experiments are well on the way to investigating this rarest of atoms.
ASACUSA is an experiment at CERN’s Antiproton Decelerator (AD) facility studying the properties of antimatter. The main thrust of ASACUSA’s research programme to date has been the creation and study of exotic atoms known as antiprotonic helium. Normal helium has two electrons orbiting its nucleus. In an antiprotonic helium atom, one electron has been replaced by an antiproton. Study of such atoms has enabled ASACUSA to measure the mass of antiprotons to very high precision. In total, five experiments use the AD’s low energy antiproton beams. ALPHA and ATRAP focus on studying antihydrogen atoms. AEgIS, an experiment under construction, will study the influence of gravity on antimatter, while ACE is an experiment investigating the effectiveness of antiprotons as a potential treatment for certain forms of cancer.
CERN, the European Organization for Nuclear Research, is the world’s leading laboratory for particle physics. It has its headquarters in Geneva. At present, its Member States are Austria, Belgium, Bulgaria, the Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Italy, the Netherlands, Norway, Poland, Portugal, Slovakia, Spain, Sweden, Switzerland and the United Kingdom. India, Israel, Japan, the Russian Federation, the United States of America, Turkey, the European Commission and UNESCO have Observer status.