Interdependence between a mechanosensitive anon channel and glutamate receivers in distal wound signals. Credit: STAR Collaboration
Evidence suggests that neutrons and protons go through a phase transition of "first order" which is a type of stop-and go temperature change when they "melt." Similar to the way ice melts, this is how energy first increases temperature and then during the transition the temperature stays constant while the energy transforms solids to liquids. Temperature can only increase once all molecules have become liquid. The melted state, which includes protons and neutrons is a mixture of quarks as well as gluons. Scientists at the Relativistic Heavy Ion Collider, (RHIC), are seeing signs of this stop and go transition. This pattern is supported by the latest data from low-energy collisions.
Scientists can find evidence of a first order phase change in QGP for more than 35 years by studying theories. To find those signatures, scientists must study QGP at a variety of energies and map out key features in tiny particles that disappear only a billionth of trillionths of a second after their formation. Scientists finally have the measurements they need thanks to RHIC's flexibility and the sophistication of STAR (Solenoidal Tracker At RHIC) detector.
RHIC is a Department of Energy (DOE Office of Science) user facility. It was created in part to study the transition of nuclear matter to a soup of free nuclei and gluons. RHIC collides and accelerates the nuclei from gold atoms at different energies in order to study how they melt into this QGP. A drop in pressure and a longer life span of the QGP would be an analogy to water freezing or melting during a phase transition.
These signs were discovered by STAR physicists who measured the sideways deflection and size of the particles. A pressure drop would decrease the "flow" and make longer-lasting systems appear larger in one dimension. To measure such small size changes, it was necessary to use particles that were less than a femtometer. This is more than a billion times smaller then the width of a human's hair. This study generated collisions at the lowest energy by running RHIC. One particle beam collided with a stationary silver foil within the STAR detector. These "fixed-target" collisions at the lowest energy extend the energy range, aligning with the patterns long thought to be part of a first-order phase shift. Scientists continue to collect and process data from a deeper scan in order to better understand the characteristics of phase transitions at different collision energies.
More information: M. S. Abdallah and al, Flow-interferometry results of Au+Au collisions at the sNN=4.5 GeV Physical Review C (2021). M. S. Abdallah and colleagues, Flow-and interferometry results of Au+Au collisions sNN=4.5 GeV (2021). DOI: 10.1103/physrevc.103.034908
