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Artist’s impression of the particle spray created when two heavy atoms collide. As the hot subatomic soup cools, newly formed particles stream out into space. Image credit: Joseph Dominicus Lap, edited
Scientists have recreated the extreme conditions of the early universe in particle accelerators and gained surprising insights into the origin of matter.
New calculations show that up to 70% of certain particles could come from later reactions and not from the initial quark-gluon soup that formed immediately after the Big BangThis discovery challenges previous assumptions about the timing of matter formation and suggests that much of the matter around us was formed later than expected. By understanding these processes, scientists can better interpret the results of collider experiments and refine their knowledge of the origins of the universe.
Recreating the extreme conditions of the early universe
The early universe was 250,000 times hotter than the core of our sun. That’s far too hot to form the protons and neutrons that make up our everyday matter. Scientists recreate the conditions of the early universe in particle accelerators by colliding atoms at nearly the speed of light. By measuring the resulting shower of particles, scientists can understand how matter was formed.
The particles measured by scientists can come from several 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 the composite particles made of quarks began to interact with each other. A new calculation found that up to 70% of some measured particles come from these later reactions, rather than from reactions similar to those of the early universe.
Understanding the origin of matter
This discovery improves scientific understanding of the origins of matter. It helps determine how much of the matter around us was created in the first fractions of a second after the Big Bang, compared to the amount of matter created by later reactions as the universe expanded. This result implies that large amounts of the matter around us were created later than expected.
To understand the results of collider experiments, scientists must ignore the particles formed in the later reactions. Only the particles formed in the subatomic soup reveal the early conditions of the universe. This new calculation shows that the number of measured particles formed in reactions is much higher than expected.
Importance of later reactions in particle formation
In the 1990s, physicists realized that certain particles form in significant numbers in later reactions after the initial formation of the universe. Particles called D mesons can interact with each other to form a rare particle, charmonium. Scientists have disagreed on how important this effect is. Because charmonium is rare, it is difficult to measure.
However, recent experiments provide data on how many charmonium and D mesons are produced in colliders. Physicists from Yale University and Duke University used the new data to calculate the strength of this effect. It turned out to be much more significant than expected. More than 70% of the charmonium measured could have been produced in reactions.
Implications for understanding the origins of matter
As the hot soup of subatomic particles cools, it expands into a fireball. All this happens in less than a hundredth of the time it takes for light to atomBecause this happens so quickly, scientists aren’t sure exactly how the fireball expands.
The new calculation shows that scientists do not necessarily need to know the details of this expansion. The collisions produce a considerable amount of charmonium anyway. The new result brings scientists one step closer to understanding the origins of matter.
Reference: “Hadronic J/ψ regeneration in Pb+Pb collisions” by Joseph Dominicus Lap and Berndt Müller, October 11, 2023, Physics Letter B.
DOI: 10.1016/j.physletb.2023.138246
This work was supported by the Nuclear Physics Program of the Department of Energy Office of Science. One of the researchers also thanks for hospitality and financial support during a sabbatical at Yale University.
