“All our observations find complete symmetry between matter and antimatter, so our universe shouldn't have existed,” says Christian Smorra of the BASE collaboration at the CERN research center. “There must be asymmetry somewhere, but we just don't understand where exactly. What breaks symmetry, what is the source?"
The search continues. Until now, no difference has been found between protons and antiprotons, and it could explain the existence of matter in our Universe. However, physicists in collaboration with BASE at the CERN Research Center have been able to measure the magnetic force of antiprotons with unprecedented accuracy. However, this data did not provide any information about how matter formed in the early universe, since particles and antiparticles should have completely destroyed each other.
The latest BASE measurements have shown the complete identity of protons and antiprotons, once again confirming the Standard Model of particle physics. Scientists all over the world use a variety of methods to find at least some differences, of any magnitude. The matter-antimatter imbalance in the Universe is one of the hottest topics of discussion in modern physics.
The multinational BASE collaboration at CERN brings together scientists from universities and institutes around the world. They compare with great accuracy the magnetic properties of protons and antiprotons. The magnetic moment is an important component of particles and can be depicted roughly as the equivalent of a miniature bar magnet. The so-called g-factor measures the strength of the magnetic field.
“The big question is whether the antiproton has the same magnetism as the proton,” explains Stephan Ulmer, a spokesman for the BASE group. "Here's a puzzle we need to solve."
The BASE collaboration presented high-precision measurements of the antiproton g-factor back in January 2017, but the current measurements are much more accurate. The current high-precision measurement has determined the g-factor to nine significant digits. This is equivalent to measuring the circumference of the earth to the nearest four centimeters. The value 2.7928473441 (42) is 350 times more accurate than the results published in January.
“This amazing increase in accuracy in such a short period of time is made possible by completely new techniques,” says Ulmer. Scientists first took two antiprotons and analyzed them using two Penning traps.
Antiprotons are artificially created at CERN, and scientists store them trapped in an experiment. The antiprotons for the current experiment were isolated in 2015 and measured from August to December 2016. In fact, this is the longest antimatter retention period of all time. Antiprotons spent 405 days in a vacuum, in which there were ten times fewer particles than in interstellar space. A total of 16 antiprotons were used, cooled to near absolute zero.
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The measured g-factor of the antiproton was compared with the g-factor of the proton, which was measured with incredible accuracy back in 2014. Ultimately no difference was found. This confirms CPT symmetry, according to which the universe has a fundamental symmetry between particles and antiparticles.
Now BASE scientists will have to develop and implement methods for even more high-precision measurement of the properties of the proton and antiproton in order to find the answer to the question of interest to everyone.