Using the world’s three most powerful particle accelerators to reveal the space-time geometry of quark matter

Physicists from Eötvös Loránd University (ELTE) have carried out research into the matter that makes up the atomic nucleus using the world’s three most powerful particle accelerators. Their goal was to map the “primordial soup” that filled the universe in the first millionth of a second following its creation.

Intriguingly, their measurements showed that the movement of observed particles resembles the search for prey of marine predators, patterns of climate change, and fluctuations in the stock market.

Immediately after the Big Bang, temperatures were so extreme that atomic nuclei could not exist, nor nucleons, their building blocks. So, in this first case, the universe was filled with a “primordial soup” of quarks and gluons.

As the universe cooled, this medium underwent a “freeze,” leading to the formation of the particles we know today, such as protons and neutrons. This phenomenon is reproduced on a much smaller scale in particle accelerator experiments, where collisions between two nuclei create tiny droplets of quark matter. These droplets eventually pass into ordinary matter through freezing, a transformation known to the researchers conducting these experiments.

However, the properties of quark matter vary due to pressure and temperature differences resulting from collision energy in particle accelerators. This variation requires measurements to “scan” matter in particle accelerators of different energies, the Relativistic Heavy Ion Collider (RHIC) in the United States, or the Super Proton Synchrotron (SPS) and the Large Hadron Collider. (LHC) in Switzerland.

“This aspect is so crucial that new accelerators are being built all over the world, for example in Germany or Japan, specifically for such experiments. Perhaps the most important question is how the transition between phases: a critical point can appear on the phase map”, explains Máté Csanád, professor of physics at the Department of Atomic Physics at Eötvös Loránd University (ELTE).

The long-term goal of the research is to deepen our understanding of the strong interaction that governs interactions in quark matter and in atomic nuclei. Our current level of knowledge in this area can be compared to humanity’s mastery of electricity in the days of Volta, Maxwell or Faraday.

While they had a notion of the fundamental equations, it took considerable experimental and theoretical work to develop technologies that profoundly transformed daily life, from the light bulb to televisions, telephones, computers and the Internet. . Likewise, our understanding of the strong interaction is still embryonic, making research aimed at exploring and mapping it vitally important.

ELTE researchers have participated in experiments at each of the accelerators mentioned above and their work over the last few years has provided a comprehensive picture of the geometry of quark matter. They achieved this through the application of femtoscopy techniques. This technique uses correlations that arise from the non-classical, quantum-like wave nature of the produced particles, which ultimately reveals the femtometric-scale structure of the medium, the particle-emitting source.

“In previous decades, femtoscopy was based on the assumption that quark matter followed a normal distribution, that is, the Gaussian shape found in many places in nature,” explains Márton Nagy, one of the group’s principal researchers. However, Hungarian researchers turned to the Lévy process, also known in various scientific disciplines, as a more general framework and which well describes the search for prey by marine predators, stock market processes or even climate change.

A distinctive feature of these processes is that at certain times they undergo very significant changes (for example, when a shark searches for food in a new area), and in such cases a Lévy distribution rather than a normal (Gaussian) distribution can occur.

This research is of significant importance for several reasons. Primarily, one of the most studied features of the freezing of quark matter, its transformation into conventional (hadronic) matter, is the femtoscopic ray (also called the HBT ray, noting its relationship with the well-known Hanbury Brown effect and Twiss in astronomy), derived from femtoscopic measurements. However, this scale depends on the supposed geometry of the medium.

As Dániel Kincses, a postdoctoral researcher in the group, summarizes: “If the Gaussian hypothesis is not optimal, then the most precise results of these studies can only be obtained under the Lévy hypothesis. The value of the “Lévy exponent”, which characterizes “The Lévy distribution can also shed light on the nature of the phase transition. Thus, its variation with collision energy provides valuable information about the different phases of matter quarks.”

ELTE researchers actively participate in four experiments: NA61/SHINE at the SPS accelerator, PHENIX and STAR at RHIC and CMS at the LHC. ELTE’s NA61/SHINE group is led by Yoshikazu Nagai, CMS group by Gabriella Pásztor; and RHIC groups by Máté Csanád, who also coordinates ELTE’s femtoscopy research.

The groups make substantial contributions to the success of experiments in a variety of capacities, ranging from detector development to data acquisition and analysis. They are also engaged in numerous projects and theoretical research. “What is unique about our femtoscopy research is that it is carried out in four experiments in three particle accelerators, giving us an overview of the possible geometry and phases of matter quarks,” says Máté Csanád.

The team presented their latest findings at the Particle Correlations and Femtoscopy Workshop, held November 6-10, 2023. In large-scale collaborations, they also published related research In The European Journal of Physics C, Physics letters B And Universe.