Comparision of modeling of prompt photon production in proton-proton collisions at energies NICA =10 GeV in PYTHIA and calculations using FeynCalc
This paper compares prompt photon production modeling in proton-proton collisions at GeV using PYTHIA 8.316 and FeynCalc, finding that quark-gluon Compton scattering dominates the cross section (51.27%) and that photon energy and rapidity distributions follow logarithmic-normal and normal laws, respectively.
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High-energy physics is the study of the universe's most fundamental building blocks and the forces that bind them. To understand how matter is constructed, scientists smash particles together at tremendous speeds, recreating conditions similar to those just after the Big Bang. In these violent collisions, protons—tiny, positively charged particles that make up the nucleus of every atom—crash into one another, shattering into a spray of new particles. Among the debris, a special type of light particle called a photon often appears. Unlike other particles produced in these crashes, photons carry no electric charge and do not feel the strong nuclear force that holds atomic nuclei together. Because they are so neutral, they can travel straight out of the collision zone without being deflected or absorbed, acting like perfect messengers that carry unaltered information about the initial impact. By studying these "prompt" photons, which are created instantly during the hard collision rather than later from the decay of other particles, researchers can peer directly into the structure of the proton and the behavior of the quarks and gluons inside it.
A team of researchers from Baku State University recently turned their attention to a specific energy range where such studies are particularly challenging. They focused on proton-proton collisions occurring at an energy of 10 billion electron volts, a level accessible at the NICA accelerator complex in Russia. This energy is lower than what is found at the world's most powerful colliders, making the physics more complex because the interactions are dominated by strong forces that are difficult to calculate with standard mathematical tools. To understand what happens at this energy, the team used two different approaches to model the production of these prompt photons. The first approach relied on a sophisticated computer program called PYTHIA, which simulates the entire chaotic process of a collision, including the initial smash, the subsequent spray of particles, and how they eventually settle into stable matter. The second approach used a different software tool, FeynCalc, to perform precise theoretical calculations based on the fundamental equations of particle physics, focusing strictly on the initial interaction without the added complexity of the later stages.
The researchers were particularly interested in three specific ways these photons are born during a collision. The first is a process called Compton scattering, where a quark (a constituent of the proton) and a gluon (the particle that carries the strong force) collide and scatter, releasing a photon. The second is the annihilation of a quark and its antimatter counterpart, an antiquark, which disappear to create a photon. The third is a process called bremsstrahlung, where a quark slows down or changes direction, emitting a photon in the process, similar to how a car braking might create a sound. By running their simulations and calculations, the team discovered that at this specific energy level, the Compton scattering process is the dominant source of prompt photons, accounting for more than half of all such events. The annihilation of quark-antiquark pairs was the second most common source, contributing nearly half of the total, while the bremsstrahlung process was found to be so rare that it contributed almost nothing to the overall picture.
When the team compared the results from the full computer simulation with the strict theoretical calculations, they found that the two methods produced very similar shapes in their data. Both methods showed that the number of photons produced drops off sharply as their energy increases, and both indicated that photons are most likely to be emitted in directions close to the path of the incoming proton beams rather than straight out from the center. However, the two methods did not agree on the exact numbers. The computer simulation, which includes the messy reality of particle showers and the formation of new matter, predicted slightly different rates than the clean, idealized equations. The researchers explained that this difference arises because the simulation accounts for the complex, non-linear effects of particles interacting with each other after the initial crash, effects that are smoothed over or ignored in the simpler theoretical formulas.
This work is significant because it helps scientists understand how to interpret data from future experiments at the NICA facility. By confirming that the dominant processes are well-understood and by quantifying exactly how much the complex simulation differs from the basic theory, the researchers provide a clearer roadmap for analyzing real-world data. They demonstrated that while simplified mathematical models are useful for understanding the core mechanics of particle collisions, modern simulation tools are essential for making accurate predictions that match the reality of what detectors will actually see. The study confirms that at these intermediate energies, the production of prompt photons is a reliable probe for studying the proton's internal structure, provided that scientists use the right tools to account for the intricate dance of forces that occurs in the split second after the collision.
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