The early universe was 250,000 times hotter than the core of our Sun, too hot to form the protons and neutrons that make up everyday matter. Scientists are recreating the conditions of the early universe in particle accelerators, smashing atoms together at nearly the speed of light.

Measuring the resulting particle flow allows scientists to understand how matter is made. The particles the scientists measured could have been created in different ways: from the original soup of quarks and gluons, or from later reactions. These later reactions began 0.000001 seconds after the Big Bang, when complex particles made of quarks began interacting with each other.

The new calculations revealed that about 70% of the particles measured came from these later reactions, rather than from similar reactions in the early universe. The study was published in the journal Physics Letters B.

This discovery advances scientific understanding of the origin of matter. It helps determine how much of the matter around us was created in the first few fractions of a second after the Big Bang, rather than how much was created in later reactions as the universe expanded.

This result means that a large amount of matter around us formed later than expected. To understand the results of the experiments at the collider, scientists need to discard the particles produced in the late reactions. Only those formed in the subatomic broth reveal the conditions of the early universe. This new calculation shows that the number of measured particles produced in the reactions is much higher than expected.

In the 1990s, physicists realized that significant amounts of certain particles were produced as a result of subsequent reactions that occurred after the early stages of the formation of the universe. Particles called D mesons can interact to form the rare charmonium particle.

Scientists were not unanimous about the significance of the effect. Charmonium is rare and difficult to measure. But recent experiments provide data on how many charmonium and D mesons are produced by colliders.

Physicists from Yale University and Duke University used new data to calculate the strength of this effect. It turns out to be much larger than expected. More than 70% of the measured charmonium can be formed in the reactions.

As the hot soup of subatomic particles cools, it expands into a fireball. All of this happens in less than one-hundredth of the time it takes for light to pass through an atom. Because it’s so fast, scientists aren’t sure exactly how the fireball expands. The new calculations show that scientists don’t need to know the details of this expansion at all. Still, the collision produces a significant amount of charmonium. The new result brings scientists closer to understanding the origins of matter.