By looking at debris from particle collisions that mimic the conditions of the universe right after the Big Bang, scientists were able to measure the force of interaction between pairs of antiprotons for the first time.

The new findings could provide insight into larger chunks of antimatter such as antimatter nuclei, and could even help solve the mystery of why the universe today is essentially devoid of antimatter, DOE/Brookhaven National Laboratory reported.

"The Big Bang-the beginning of the universe-produced matter and antimatter in equal amounts. But that's not the world we see today. Antimatter is extremely rare. It's a huge mystery!" said Aihong Tang, a Brookhaven physicist involved in the analysis. "Although this puzzle has been known for decades and little clues have emerged, it remains one of the big challenges of science. Anything we learn about the nature of antimatter can potentially contribute to solving this puzzle."

The conditions within the Relativistic Heavy Ion Collider (RHIC) where the study was conducted make it one of the few places on Earth where antimatter can be abundantly produced. The rare matter is created by slamming the nuclei of heavy atoms like gold into each other at the speed of light. These conditions are similar to what occurred in the very early universe, only microseconds after the Big Bang.

To study the simple interaction of unbound antiprotons and gain insight into the force between the antiprotons, the researchers used data collected by RHIC's STAR detector. They searched the data for pairs of antiprotons that were close enough to interact as they emerged from the fireball produced by the original collision.

"We see lots of protons, the basic building blocks of conventional atoms, coming out, and we see almost equal numbers of antiprotons," said Zhengqiao Zhang, a graduate student in Professor Yu-Gang Ma's group from the Shanghai Institute of Applied Physics of the Chinese Academy of Sciences, who works under the guidance of Tang when at Brookhaven. "The antiprotons look just like familiar protons, but because they are antimatter, they have a negative charge instead of positive, so they curve the opposite way in the magnetic field of the detector."

Looking at which antiprotons struck each other allowed the team to measure the correlation of certain properties, revealing the strength of the force between them and the range over which it acts. The findings revealed the force between antiprotons is attractive, similar to the nuclear force that holds ordinary atoms together. When these antiprotons are close enough together, the strong force overcomes the tendency of the particles to repel one another, allowing the positively charged protons to bind to each other within the nuclei of an ordinary atom. The researchers were surprised to find the no difference between matter and antimatter in the way in which their forces behaved, making them appear perfectly symmetrical. The finding means there is no asymmetrical "quirk" of strong force that explains why there is so much ordinary matter and so little antimatter in the universe today.

"The successful implementation of the technique used in this analysis opens an exciting possibility for exploring details of the strong interaction between other abundantly produced particle species," concluded Richard Lednický, a STAR scientist from the Joint Institute for Nuclear Research, Dubna, and the Institute of Physics, Czech Academy of Sciences, Prague.

The findings were published in a recent edition of the journal Nature.