Monday, February 26

Flow of hypernuclei measured at RHIC 2023

Physicists at the Relativistic Heavy Ion Collider (RHIC) discovered directed hypernuclei flow. These rare, short-lived nuclei contain at least one “hyperon” along with protons and neutrons.

Neutron stars, the densest and most unusual objects in the cosmos, may contain huge amounts of this material.

Even if neutron stars are still science fiction, particle collisions can provide scientists with information about these celestial objects from a lab on Earth.

In the study, LBNL physicist Xin Dong said, “The conditions in a neutron star may still be far from what we reach at this moment in the laboratory, but at this stage, it’s the closest we can get, By comparing our data from this laboratory environment to our theories, we can try to infer what happens in the neutron star.”

Hyperons have one “strange” quark instead of an up or down quark.

The RHIC STAR detector was used to study gold nuclei debris flow patterns. Crash pressure gradients caused the patterns. They researched hyperon-nucleon interactions.

Yapeng Zhang, another STAR member from the Institute of Modern Physics of the Chinese Academy of Sciences, led the data analysis alongside his student Chenlu Hu. “In our normal world, nucleon-nucleon interactions form normal atomic nuclei. But as we enter a neutron star, hyperon-nucleon interactions—which we don’t know much about—become highly crucial to structure.”

Monitoring hypernuclei should reveal the hyperon-nucleon interactions that create these unique particles.

The Physical Review Letters discoveries will help theorists enhance their models of hyperon-nucleon interactions that create hypernuclei and neutron stars’ enormous structures.

Zhang stated, “There are no solid calculations to establish these hyperon-nucleon interactions; this measurement may constrain theories and provide a variable input for calculations.”

The more protons and neutrons a nucleus contains, the greater collective flow it shows in a particular direction, according to previous study.

In this work, STAR results show that hypernuclei exhibit the same mass-scaling tendency, suggesting they are generated by the same mechanism.

Coalescence, regulated by the strong nuclear force, teaches them about nucleon interaction.

The strong nuclear force governs these nuclei’s protons and neutrons’ flow.

The scientists believe that nucleons and hyperons interact similarly based on their flow patterns and mass scaling relationship.

The flow patterns show particle collision matter’s temperature, density, and other properties.

“The collision pressure gradient will cause asymmetry in the outgoing particle direction. The flow shows how nuclear matter creates a pressure gradient. Zhang stated.

“The measured flow of hypernuclei may open a new door to study hyperon-nucleon interactions under finite pressure at high baryon density,” he added.

The scientists will monitor hypernuclei interactions to understand more about the medium.

RHIC’s wide impact energy spectrum made this research possible. Phase I of the RHIC Beam Energy Scan examined gold-gold collisions from 200 GeV to 3 GeV.

One gold ion beam travelling across the 2.4-mile RHIC collider collided with a gold foil within the STAR detector to reach the lowest energy. Scientists can achieve the highest “baryon density,” a measure of collision pressure, due to low power.

Yue-Hang Leung, a postdoctoral fellow at Heidelberg University in Germany, said, “At this lowest collision energy, where the matter created in the collision is very dense, nuclei and hypernuclei are produced more abundantly than at higher collision energies. The low-energy collisions are the only ones that produce enough of these particles to give us the statistics we need to do the analysis. This is unprecedented.”

What did RHIC scientists discover about neutron stars? Hypernuclei arise via coalescence like normal nuclei, suggesting they are created late in the collision system’s history.

“At this late stage, the density for the hyperon-nucleon interaction we see is not that high,” the researcher stated.

Dong stated. “These experiments may not directly simulate the neutron star environment.”

“This data is fresh. Theorists must weigh in. The new neutron star model must contain this hyperon-nucleon interaction data. We need experimentalists and theorists to interpret and link this data.”

The National Science Foundation and DOE Office of Science (NP) sponsored this study.

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