AsianScientist (Oct. 26, 2017) – Scientists in Japan and Germany have discovered that the magnetic moments of the proton and antiproton are extremely similar, with implications on how our universe came to be dominantly populated by matter rather than antimatter particles. They published their findings in Nature.
During the Big Bang, equal amounts of matter and antimatter should have been created because matter and antimatter particles are produced as a pair. Yet, nearly everything on Earth is made of matter, with antimatter being exceedingly scarce. For decades, scientists have been trying to understand how the imbalance between matter and antimatter in the universe came to be.
In this study, researchers from the University of Tokyo, the Max Planck Institute for nuclear physics, the University of Mainz, the University of Hannover and GSI Darmstadt have placed new constraints on the difference between matter and antimatter, as part of the quest to discover why our Universe is almost only composed of matter.
Using a two-particle measurement method, the group measured the magnetic moment of the antiproton at a precision 350 times higher than any previous measurement. The technique was developed in Professor Stefan Ulmer’s RIKEN laboratory, which is a further advance of a two-trap method previously developed at the University of Mainz.
The system involves the simultaneous entrapment and measurement, within an even magnetic field, of two separate antiprotons—one measured at a relatively high temperature of about 350 degrees Kelvin (K)—a temperature equivalent to hot water—and the other at just 0.15 K, extremely close to absolute zero.
The first antiproton is used to calibrate the magnetic field, by measuring a property called the ‘cyclotron frequency,’ while the other is used to measure a quality known as the Larmor frequency, which looks at the change in the orientation of a rotating particle’s spin, allowing precise measurements of the magnetic moment.
They showed that the magnetic moments of the proton and antiproton are tremendously close, meaning that the so-called ‘charge, parity and time (CPT) asymmetry’—a key factor in the lack of antimatter—must be very small, if it exists at all.
In addition, the results also put strict limits on the possibility that a difference in the magnetic moments could have caused a process of ‘spontaneous symmetry breaking’ at the high energies that existed in the early universe, leading to differences in matter and antimatter.
“With these results, we have shown, as has been demonstrated with other properties of a variety of particles, that CPT invariance seems to hold at very high precision, as the magnetic moment of the proton and the antiproton still look identical, apart from the signs,” said Ulmer.
“This result is the culmination of many years of continuous research and development, and the successful completion of one of the most difficult measurements ever performed in a Penning trap instrument, with many parameters developed close to the principal technical limits,” he added.
“By upgrading the experiment with several new technical innovations, we feel that some further improvement can still be made, and in the future, following the CERN upgrade expected to finish in 2021, we will be able to achieve an at least ten-fold improvement,” said Dr. Christian Smorra of RIKEN who is the first-author of the study.
The article can be found at: Smorra et al. (2017) Parts-per-Billion Measurement of the Antiproton Magnetic Moment.
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Source: RIKEN.
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