ALICE Illuminates the Structure of the Nucleus

ALICE Illuminates the Structure of the Nucleus
ALICE Illuminates the Structure of the Core - An example of ultra-peripheral collision at the LHC showing how two lead ion beams pass closely by each other without interacting. Electromagnetic interactions occur when photons from one beam collide with those from another. When analyzed with higher-energy photons, the structure of gluonic matter in the nucleus becomes more apparent. (Photo: CERN)

The new ALICE findings provide insight into the composition of gluonic matter in the LHC. Proton and lead beams in the Large Hadron Collider travel at nearly the speed of light. They carry a strong electromagnetic field that acts like a stream of photons as they pass through the beam accelerator.

When one of the two beams in the LHC pass close to each other without colliding, it can release a very high-energy photon that strikes the other beam. Collisions between photons and nuclei, protons or even other photons can result from this. To better understand protons and the internal structure of nuclei, the ALICE team is studying these collisions. New findings on this topic were presented at the LHCP 2023 conference.

Photons are the best tools for examining the interior of nuclei. A quark-antiquark pair is typically created when a photon collides with a nucleus, exchanging two gluons, the force carriers of the strong interaction. Researchers further divide these collisions into two categories: coherent collisions, in which a photon connects with the entire nucleus, and inconsistent collisions, in which a photon interacts with a single nucleon.

Scientists are looking for large numbers of gluons, indicating a large concentration of gluons inside the nuclei. According to theoretical models, gluon densities increase as nuclei approach the speed of light. If the density increases enough, the core will be saturated with gluonic material, which will prevent the amount of gluons from increasing further. One of the most important open questions in the science of strong interactions is how to directly investigate gluonic saturated matter. By doing this we can learn more about the internal organization of protons and nuclei.

J/ψ meson generation occurs when a charm quark-antiquark pair is created after a photon-nucleus collision. To investigate gluon saturation effects, the researchers examine how coherent J/ψ production changes with photon energy. As the photon energy increases, it becomes easier to "see" the gluonic matter inside the nuclei. Using LHC Run 2 data, the new ALICE results for J/ψ generation cover a wider momentum range compared to previous measurements in Run 1. These results are consistent with predictions made by gluon-saturation models.

The chance to analyze the geometrical arrangements of quantum fluctuations in the internal structure of the proton is provided by inconsistent collisions. The ALICE collaboration achieves this by examining the momentum distribution transferred to the J/ψ meson. The partnership demonstrated in a recent study that gluonic hotspots (regions of saturated gluonic matter) are required to fully explain this momentum transfer.

The ALICE collaboration in LHC Studies 3 and 4 will continue to examine these phenomena. Here, high-precision measurements with larger data samples will provide more powerful tools for understanding the function of saturation and gluonic hotspots.


📩 18/07/2023 15:38