Newswise — Researchers from China's IMP, together with colleagues in the RHIC-STAR project, have witnessed the group movement of hypernuclei in heavy-ion collisions, marking a groundbreaking observation. This discovery opens up fresh avenues for investigating interactions between hyperons and nucleons in high-density nuclear environments. The findings were recently published in Physical Review Letters on May 24th.
Hyperons, consisting of a strange (s) quark, differ from nucleons (protons or neutrons) which only contain up (u) and down (d) quarks. These two types of particles can combine to create bound structures known as "hypernuclei." Theoretical predictions propose that hyperons may exist within the cores of neutron stars, which form when extremely massive stars collapse. However, the presence of hyperons alters the equation of state of nuclear matter, leading to challenges in constructing theoretical models for massive neutron stars. This intriguing predicament is commonly referred to as the "hyperon puzzle" within the field of neutron star research.
The experimental determination of the Y-N interaction strength in a dense nuclear medium is crucial for unraveling the "hyperon puzzle." Additionally, this endeavor holds immense significance in advancing our comprehension of quantum chromodynamics (QCD), the theory of strong interactions. The observation of collective flow in hypernuclei presents a promising avenue for extracting Y-N interactions in dense nuclear matter, thereby offering a potential solution to the perplexing "hyperon puzzle."
High-energy heavy ion collisions serve as a distinctive method for investigating the characteristics of dense nuclear matter within controlled laboratory settings. In these collisions, the presence of dense nuclear matter induces a pressure gradient, leading to the emergence of collective flow phenomena such as directed flow and elliptic flow among particles. Scientists have successfully observed collective flow effects in mesons, baryons, and light nuclei through experimental studies. However, due to the infrequent production of hypernuclei, there has been a scarcity of experimental data pertaining to the collective flow of hypernuclei.
The research experiment was conducted at the Relativistic Heavy Ion Collider (RHIC), situated at the Brookhaven National Laboratory in the United States. Utilizing 3 GeV Au-Au collision data obtained from the Solenoidal Tracker at RHIC (STAR) experiment, scientists reconstructed approximately 8400 hypertritons (hypernuclei composed of a Λ hyperon, a proton, and a neutron) and roughly 5200 hyperhydrogen-4 hypernuclei (hypernuclei comprising a Λ hyperon, a proton, and two neutrons). This remarkable dataset represents the largest statistical sample of experimentally observed hypertritons and hyperhydrogen-4 hypernuclei to date.
This research provides a fresh avenue for investigating Y-N interactions in the presence of finite pressure, which is crucial for bridging the gap between nuclear collisions and the equation of state that governs the internal composition of compact stars. By exploring the collective flow of hypernuclei in heavy-ion collisions, this study contributes to our understanding of the relationship between Y-N interactions and the equation of state, shedding light on the inner structure of compact stars.
The research conducted at RHIC involved the collaboration of an international team known as STAR, comprising over 700 researchers from 71 institutions across 14 countries. Led by Prof. ZHANG Yapeng's team from IMP, the study was a collective effort. The principal authors of this research included collaborators from IMP, namely HU Chenlu (PhD student), Dr. HE Xionghong, and ZHAO Fengyi (PhD student). Additionally, Dr. DONG Xin, Dr. JI Yuanjing, and Dr. LEUNG Yue-Hang from the Lawrence Berkeley National Laboratory in the U.S. also played significant roles as principal authors in this study.
RSS