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physics

Protons and antihydrogen

Chukman So / University of California, Berkeley | Max Planck Institute for Nuclear Physics The trajectories of the antihydrogen atom in an experiment carried out at CERN in 2016 (top), and the Penning trap, used to trap protons (above)Chukman So / University of California, Berkeley | Max Planck Institute for Nuclear Physics

Two pieces of news from the atomic world. The first is that scientists have increased the precision with which they can measure the mass of a proton, the particle with a positive electric charge that exists in the nucleus of all atoms. The mass of a proton is one of the factors that determine how electrons move around the atomic nucleus. Teams from the Max Planck Institute for Nuclear Physics in Germany and the Riken Laboratories in Japan increased the precision of the measurement by a factor of three. The new measurement was taken by comparing a single proton moving in a magnetic field with the mass of the nucleus of a carbon-12 atom, which is composed of six protons and six neutrons, and is used as the standard for measuring atomic mass. With a precision of 32 parts per trillion, the new proton mass value is 1.007276466583 atomic mass units, slightly smaller than previously measured (Physical Review Letters, July 18). The other news is that a group of 50 physicists from 17 research institutions has reported the first detailed observation of the fine spectral lines of an antimatter atom known as antihydrogen, which has the same characteristics as hydrogen, but with the opposite electrical charges. The observation was made using equipment at the European Organization for Nuclear Research (CERN), on the border between Switzerland and France. The researchers irradiated antihydrogen atoms with microwaves, and in response, the anti-atoms revealed their identity by emitting or absorbing energy at specific frequencies. These patterns are known as spectral lines and are unique to each atom, like fingerprints. As expected, the antihydrogen spectral lines match very closely to those of hydrogen, which are already well known (Nature, August 3).

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