Physicists narrow down strong nuclear force critical point
Researchers have made progress in identifying a critical point where the strong nuclear force weakens, allowing quarks and gluons to form a hot plasma. By analyzing collisions at a New York particle accelerator, scientists have narrowed the possible location of this point on a phase diagram. This finding could reveal insights into the early universe and neutron stars.
The strong nuclear force, nature's strongest interaction, binds quarks and gluons into protons and neutrons. For decades, physicists have sought a "critical point" where this force abruptly loosens, similar to the triple point in water where liquid, ice, and vapor coexist. Such a point would mark a sharp transition to a quark-gluon plasma, a soupy state of matter created in high-energy collisions.
Xin Dong at Lawrence Berkeley National Laboratory in California led a team that examined data from collisions of gold ions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in New York. They studied the number and distribution of particles produced, aiming to map a phase diagram for quark-gluon matter under varying temperatures and pressures. While the analysis did not precisely locate the critical point, it significantly constrained the region where it might exist.
"We were effectively trying to create a phase diagram for quarks and gluons," Dong said. The experiment revealed a gradual "melting" into plasma in some areas, but the critical point would involve a sudden shift, akin to ice chunks forming in water.
Agnieszka Sorensen at the Facility for Rare Isotope Beams in Michigan, who was not involved, noted that the work guides future searches and highlights key particle properties as indicators. Claudia Ratti at the University of Houston praised the precision, especially in a theoretically challenging diagram region, and called for analysis at lower energies where predictions converge.
Dong emphasized that detecting the critical point would be a "generational breakthrough." The strong force is unique among fundamental forces in potentially having such a point, and it influenced the hot, dense matter post-Big Bang and governs neutron star structures. Completing the phase diagram could illuminate these cosmic phenomena.
The findings appear in Physical Review Letters (DOI: 10.1103/9l69-2d7p).