Advancements in Our Understanding of Matter-Antimatter Symmetry

Researchers from the Institute of Modern Physics (IMP) at the Chinese Academy of Sciences have made a groundbreaking discovery with the identification of a new antimatter hypernucleus named antihyperhydrogen-4. This represents the heaviest antimatter hypernucleus observed to date.

According to current physics, matter and antimatter were supposed to be evenly matched at the start of the universe. But something mysterious happened that led to the destruction of almost all of both. As a result, only about one in ten billion matter particles survived. These leftover particles eventually came together to form the universe we see around us today.

What caused the difference in quantities of matter and antimatter in the universe? To answer this question, an important approach is to create new antimatter in the laboratory and study its properties.

Hao Qui, Professor, Institute of Modern Physics

In today’s matter-dominated universe, antimatter is incredibly rare because it annihilates almost instantly when it encounters matter. Creating antimatter nuclei, especially those with hyperons like Lambda particles, is even more challenging. Despite the Dirac equation predicting the existence of antimatter back in 1928, scientists have discovered only six types of antimatter (hyper)nuclei over nearly a century.

Recently, scientists at the Relativistic Heavy Ion Collider (RHIC) in the United States managed to produce antihyperhydrogen-4. RHIC accelerates heavy ion beams to nearly the speed of light, causing them to collide in experiments that mimic the conditions of the early universe. These high-energy collisions create fireballs with temperatures reaching several trillion degrees, where matter and antimatter are roughly balanced. As the fireball expands and cools rapidly, some antimatter survives long enough to be detected by the STAR detector.

Antihyperhydrogen-4 consists of one antiproton, two antineutrons, and one anti-Lambda hyperon. Due to the presence of the unstable anti-Lambda hyperon, antihyperhydrogen-4 decays after traveling just a few centimeters.

After analyzing experimental data of approximately 6.6 billion heavy-ion collision events, we reconstructed antihyperhydrogen-4 from its decay products antihelium-4 and π⁺ meson, and identified a signal of about 16 antihyperhydrogen-4.

Junlin Wu, PhD Student, Institute of Modern Physics

To further confirm the symmetry between matter and antimatter qualities, the researchers also tested the lifetime of antihyperhydrogen-4 and found no discernible variation between it and that of its counterpart particle, hyperhydrogen-4, within the limits of measurement precision.

The discovery and study of antihyperhydrogen-4 represent a significant advancement in antimatter research and enhance our understanding of matter-antimatter symmetry.

Journal Reference:

STAR Collaboration. (2024) Observation of the antimatter hypernucleus ${}_{\stackrel{¯<!--\; ¯\; -->}{\mathbf{\Lambda <!--\; ?\; -->}}}{}^{\mathbf{4}}\stackrel{¯<!--\; ¯\; -->}{\mathbf{H}}$. Nature. doi.org/10.1038/s41586-024-07823-0.