Immediately after the Big Bang, there was what is called “primordial soup,” a hot plasma of quarks and gluons. The Large Hadron Collider (LHC) at the European Center for Nuclear Research (CERN), the most powerful particle accelerator built to date, wants to recreate the conditions when matter and antimatter were formed in equal parts.
One of the objectives is to solve the mystery of what happened next: why did matter prevail over antimatter and invade the Universe? An enigma still to be solved, but scientists take a step forward: during collisions between ions and heavy elements, The Large Ion Collider Experiment (ALICE) found traces of the heaviest antimatter particle ever found, antihyperhelium-4.
Heavy particle collisions
During the ALICE experiments, heavy particles such as ions and lead nuclei accelerated and collided to generate exotic hypernuclei and their antimatter counterparts in the primordial plasma replica. Hypernuclei contain protons and neutrons; like normal atomic nuclei, and also unstable particles called “hyperons”, which in turn are composed of fundamental particles called “strange quarks”.
However, it is not so easy to obtain hypercores. Until recently, scientists had only been able to identify the lightest possible hypernucleus, called “hypertriton,” and its antimatter counterpart, “antihypertriton.” In early 2024, researchers at the Relativistic Heavy Ion Collider (RHIC) in New York managed to detect another antimatter particle, antihyperhydrogen-4, composed of an antiproton, two antineutrons and a particle containing quarks, called “antilambda”.
For many years, the gravitational interaction of antimatter was debated. Does it respond repulsively or is it attracted? CERN gave an answer: antihydrogen falls downwards.
The heaviest antimatter particle
The current announcement from CERN is the detection of another antimatter particle, the heaviest ever found: antihyperhelium-4, composed of two antiprotons, an antineutron and an antilambda. Its collision occurred in 2018, but it took years of work and application of artificial intelligence to track its disintegration into other particles. ALICE helped determine the mass of antihyperhelium-4, consistent with current theory of particle physics, and the number of particles produced by lead-lead collisions, confirming that matter and antimatter are produced equally in the plasma of quarks and gluons.
The mystery of the imbalance between matter and antimatter in the Universe has not yet been unraveled, but we may be a little closer.
Article originally published in WIRED Italyadapted by Alondra Flores.
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