Semicentral or main accidents of lead nuclei in the LHC produce quark-gluon plasma and a mixed drink with contributions of other particles. Simultaneously, clouds of photons surrounding the nuclei clash, leading to the production of lepton-antilepton sets within the plasma and mixed drink, and in the area around the nuclei. Credit: IFJ PAN
When heavy ions, sped up to the speed of light, hit each other in the depths of European or American accelerators, quark-gluon plasma is formed for split seconds, or perhaps its “cocktail” experienced with other particles. According to researchers from the IFJ PAN, speculative information reveal that there are ignored stars on the scene: photons. Their accidents cause the emission of apparently excess particles, the existence of which might not be discussed.
Quark-gluon plasma is unquestionably the most unique state of matter so far understood to us. In the LHC at CERN near Geneva, it is formed throughout main accidents of 2 lead ions approaching each other from opposite instructions, taking a trip at speeds really near that of light. This quark-gluon soup is likewise in some cases experienced with other particles. Unfortunately, the theoretical description of the course of occasions including plasma and a mixed drink of other sources stops working to explain the information gathered in the experiments.
In a post released in Physics Letters B, a group of researchers from the Institute of Nuclear Physics of the Polish Academy of Sciences in Cracow discussed the factor for the observed disparities. Data gathered throughout accidents of lead nuclei in the LHC, in addition to throughout accidents of gold nuclei in the RHIC at Brookhaven National Laboratory near New York, start to concur with the theory when the description of the procedures takes into consideration accidents in between photons surrounding both engaging ions.
“With a pinch of salt, you could say that with sufficiently high energies, massive ions collide not only with their protons and neutrons, but even with their photon clouds,” states Dr. Mariola Klusek-Gawenda (IFJ PAN) and right away clarifies: “When describing the collision of ions in the LHC we already took into account collisions between photons. However, they concerned only ultra-peripheral collisions, in which the ions do not hit each other, but pass by each other unchanged, interacting only with their own electromagnetic fields. No one thought that photon collisions could play any role in violent interactions where protons and neutrons merge into a quark-gluon soup.”
In conditions understood from daily life, photons do not hit each other. However, when we are handling enormous ions sped up to practically the speed of light, the scenario modifications. The gold nucleus includes 79 protons, the lead nucleus as lots of as 82, so the electrical charge of each ion is likewise often times higher than the primary charge. The providers of electro-magnetic interactions are photons, so each ion can be dealt with as a things surrounded by a cloud of lots of photons. Moreover, in the RHIC and LHC, the ions move at speeds near that of light. As an outcome, from the viewpoint of the observer in the lab, both they and their surrounding clouds of photons seem incredibly thin spots, flattened in the instructions of motion. With each passage of such a proton-neutron pancake, there is an incredibly violent oscillation of the electrical and electromagnetic fields.
In quantum electrodynamics, the theory utilized to explain electromagnetism with regard to quantum phenomena, there is an optimum vital worth of the electrical field, of the order of 10 to sixteen volts per centimeter. It uses to fixed electrical fields. In the case of accidents of enormous atomic nuclei in the RHIC or LHC, we are handling vibrant fields appearing just for millionths of a billionth of one billionth of a 2nd. For such an incredibly brief time, the electrical fields in the accidents of ions can be even 100 times more powerful than the vital worth.
“In fact, the electric fields of ions colliding in the LHC or RHIC are so powerful that they generate virtual photons and their collisions occur. As a result of these processes, lepton-antilepton pairs are formed at various points around the ions where there was nothing material before. The particles of each pair move away from each other in a characteristic way: typically in opposite directions and almost perpendicular to the original direction of the movement of the ions,” discusses Dr. Wolfgang Schäfer (IFJ PAN) and explains that the household of leptons consists of electrons and their more enormous equivalents: muons and tauons.
Photon interactions and the production of lepton-antilepton sets connected with them are vital in peripheral accidents. Collisions such as these were explained by the physicists from Cracow a couple of years earlier. To their surprise, they have actually now handled to reveal that the exact same phenomena likewise play a substantial function in direct accidents of nuclei, even main ones. The information gathered for gold nuclei in the RHIC and lead nuclei in the LHC reveal that throughout such accidents a specific “excess” variety of electron-positron sets appears, which diverge reasonably gradually in instructions practically perpendicular to the ion beams. It has actually been possible to discuss their presence exactly simply by considering the production of lepton-antilepton sets by clashing photons.
“The real icing on the cake for us was the fact that by supplementing the existing tools for the description of massive ion collisions with our formalism built on the so-called Wigner distribution function, we could finally explain why the detectors of the largest contemporary accelerator experiments record these sorts of distributions of leptons and antileptons escaping from the site of the nuclear collisions (for a determined centrality of the collision). Our understanding of the most important processes taking place here has become more complete,” concludes Prof. Antoni Szczurek (IFJ PAN).
Reference: “Centrality dependence of dilepton production via γγ processes from Wigner distributions of photons in nuclei” by Mariola Klusek-Gawenda, Wolfgang Schäfer and Antoni Szczurek, 30 January 2021, Physics Letters B.
DOI: 10.1016/j.physletb.2021.136114
Work on the Cracow design of photon-photon accidents was funded by the Polish National Science Centre. The design has actually excited the interest of physicists dealing with the ATLAS and ALICE detectors of the LHC and will be utilized in the next analyses of speculative information.
