New research results from CERN confirm the standard model of physics. The existence of the universe thus remains a mystery.
CERN Research Institute, 5 JANUARY, 2022: The good news is: the standard model lasts. The bad: we still don't know why the universe exists. The team of the baryon-antibaryon-symmetry experiment (base) did not find any differences between protons and antiprotons in the most accurate measurement to date. The base is an experiment for research into antimatter at the European nuclear research center Cern.
Antiparticles have the opposite electrical charge of the particles that make up matter. Theoretically, both types of particles should have the same properties and both should have been created in the same amount during the Big Bang. However, when matter and antimatter meet, they annihilate each other. So there is obviously an asymmetry. Because both did not extinguish each other, but the universe came into being. However, what the asymmetry consists of has not yet been clarified.
One possible difference could have been in the mass. The base team around Stefan Ulmer has now largely ruled out that. Between December 2017 and May 2019, it measured the ratio of electrical charge to mass of protons and antiprotons with record precision. The evaluation took claims to one and a half years. The result has now been published.
The measurements were much more accurate than previous ones
It has been shown that there is no difference in the mass of the two. The result of the measurements agrees with the fundamental invariance when reversing charge, parity, and time (CPT), the researchers write in the journal Nature. The measurements would have an accuracy of 16 parts in a trillion. The measurements are more accurate by a factor of four than the previous ones.
This means that the mass of protons and antiprotons is identical - except for eleven places. "We have ruled out with high precision, that there is a difference in mass between protons and antiprotons", Ulmer told the news magazine Der Spiegel (paywall).
For their experiments, the researchers first generated antiprotons and caught them in an electromagnetic container, the so-called Penning trap. In this case, a particle vibrates with a characteristic frequency that is defined by its mass. Over the course of a year and a half, the researchers made over 24,000 frequency measurements.
What is the influence of gravity?
The duration of the measurement series enabled a second comparison: the effect of gravity. According to the weak equivalence principle, all particles are accelerated equally by gravity - this applies to matter and antimatter. During the measurement period, the earth orbited the sun more than once. The influence of the gravitational pull of the sun changes on the elliptical orbit.
The question was how protons and antiprotons would react to the fluctuations. But there were no differences here either. The researchers could not find any anomalous interaction between antimatter and gravity.
The results confirm the Standard Model, according to which matter and antimatter are symmetrical. But that doesn't explain our existence. This is "one of the great puzzles in fundamental physics to which we have not yet got an answer," said Ulmer. "If you put the Big Bang Theory and the Standard Model of particle physics together, then at the beginning of the universe, matter and antimatter should have been created in equal quantities. And when a particle and its antiparticle meet, they annihilate each other. But somehow it's 13.8 billion ago Years still matter remained, otherwise we would not exist."
According to Ulmer, there is a possibility that protons and antiprotons will show differences beyond the values now measured. Another possibility could be differences in the magnetic moments. The team is already researching this. "But even here," says Ulmer, "we have not yet seen any differences between protons and antiprotons."