Nucleon size restriction with relativistic nuclear collisions

A model that assumes smaller protons and neutrons and a “lumpy” arrangement of these building blocks (left) fits experimental data about the initial energy density in heavy ion collisions better than a model with larger protons and neutrons and a smoother structure (right). Credit: Brookhaven National Laboratory

It can be hard to imagine that debris from the collision of heavy ions – which melts the boundaries of protons and neutrons and produces thousands of new particles – can be used to get a detailed look at the properties of nucleons. However, new developments in experimental methods combined with improved theoretical modeling have made this possible. Based on the latest model of the colliding nuclei and the hydrodynamic evolution of the quark-gluon plasma produced in the collision, physical review messages The study shows that certain observations are highly sensitive to the size of the protons and neutrons within the colliding nuclei.

Comparing the model with data from experiments also indicates that the distribution of gluons within protons and neutrons is somewhat lumpy—not as smooth and spherical as in models using naive assumptions. Current and future measurements using collisions of different nuclei at the Relative Heavy Ion Collider (RHIC), a Department of Energy (DOE) User Facility at Brookhaven National Laboratory, and the Large Hadron Collider (LHC) at CERN, along with a cutting-edge theoretical program, will provide a more detailed look. On the distribution of gluons within protons and neutrons, in and out of heavy nuclei, and how it behaves with changing collision energy. This important information will essentially be explored at a higher resolution at the Electron-Ion Collider that will be built in Brookhaven.

The nuclei of atoms are made up of protons and neutrons, which are collectively referred to as nucleons. Nucleons, in turn, are made up of quarks and gluons. Understanding how these inner building blocks are distributed within nuclei can reveal how large protons and neutrons appear when examined at high energy. This work used comparisons between model calculations and new accurate data from collisions of heavy ions (which contain many protons and neutrons) to arrive at the distribution of gluons and to predict the size of the proton.

Determining and accurately quantifying the critical factors for nucleon size will help physicists describe Quark-gluon plasma (QGP). This is a dense, hot form of nuclear matter that is created in an individual protons The neutrons “dissolve” in it Heavy ion collision, imitating the conditions of the early universe. This knowledge can eliminate significant uncertainties about the initial state of the produced QGP. Knowing more about the initial state of QGP provides input for Model Calculations which scientists use to infer the viscosity and other properties of QGP. The results also add to measurements of the size of a proton based on the distribution of quarks within the proton.


Shedding light on the inner details and the disintegration of deuterons


more information:
Giuliano Giacalone et al., Nucleon size restriction with relativistic nuclear collisions, physical review messages (2022). DOI: 10.1103/ PhysRevLett.128.042301

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US Department of Energy


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