In the microcosm invisible to our eyes, a hidden and fierce war is being waged. The stage of this war is set in the depths of the atomic nucleus, and the protagonists are the mysterious quarks and gluons. Now, let's lift the curtain on this quantum power contest.
Glue, as the name suggests, is the "glue" that holds quarks together. They may be small, but they carry the most powerful force in the universe - power. This force acts like an indestructible chain, binding the three quarks tightly and forming hadron particles such as protons and neutrons that build the nucleus of an atom. An eternal symbiotic relationship is formed between quarks and gluons.
Back in 1979, 25 years ago, Germany's Dechs Electron Synchrotron Laboratory (DESY) unveiled the mystery of the perfect pair. Desy's scientists operate a new particle accelerator, the Petra Ring, which causes electrons and positrons to collide at nearly the speed of light, converting them into pure energy, which is then quickly converted into matter — a pair of quarks and antiquarks.
But the pair of nascent quarks are not alone. According to the predictions of quantum chromodynamics (QCD), gluons representing strong strength should also be present. This was confirmed by experimental results, with the detector capturing three quark anti-quark jets, one of which was significantly different. This is the first direct observation of gluon evidence.
The discovery was made by four teams: Tasso, Jade, Mark J, and Pluto. Their collaboration is a great story in the scientific community. Xiulan Wu and Georg Zobernig of the Tasso group devised a new algorithm for the analysis of complex multi-jet structures; For the first time, the JADE group accurately determined the coupling constant of the strong force. This momentous discovery would not have been made so quickly without the remarkable work of Desy's accelerator physicists and engineers, especially Gustav Adolf Wirth, director of the accelerator department, and his team.
Although quark and gluon are inseparable, they can never make contact like intimate partners. Their relationship is like that of a pursuer and a fugitive in a game, the closer they get, the more the powerful color forces throw them away. Scientists can only speculate on the presence and interaction of quarks and gluons by detecting the distribution and energy of particles in the jets produced by accelerators.
Quantum chromodynamics refers to this force as a "color charge," similar to the charge that produces the electromagnetic force. However, the color charge is not a color in the visible spectrum, but an abstract label. Quarks can carry any of the three color charges of red, green, and blue, and gluons transfer these color charges between them. Therefore, 8 different types of gluons are theoretically needed, and they are as colorful as a rainbow bridge.
When the struggle in the quantum realm subsides, quarks and gluons will rapidly recombine to give birth to new particles—mesons and baryons. Musons are made up of two quarks, whereas baryon is made up of three quarks. Just as human society is finally moving towards an era of peace, quarks and gluons who have experienced struggles are also moving towards reconciliation.
In extreme heat, high-energy environments, everything can change dramatically. In the first few microseconds after the universe was large**, the entire universe was filled with a "quark-gluon plasma soup", and quarks and gluons floated freely. It's like a quantum barbecue party, the temperature is extremely high, and it can't tie these particles together. It wasn't until the universe cooled rapidly that they regrouped to form the "Quark-Guon Alliance".
Scientists are simulating this "wild" state in an accelerator in an attempt to recreate what the universe originally looked like. For example, at CERN, they had heavy nuclei collide at the speed of light, creating a miniature "barbecue tray." In this blazing environment, protons and neutrons "melt" and turn back into free quarks and gluons. But soon, this small universe cooled down, and quarks and gluons had to recombine to form new hadron jets.
By measuring the behavior and distribution of these jets during the "quenching" process, the scientists found that the quark-gluon plasma behaves more like a "perfect fluid" with little to no fluidity. This presents us with a new mystery: why would such a powerful force show such a supple side? Perhaps, in extreme environments, the quantum world will open a new door for us to explore.
From the initial discovery of clues to gluons, to the current deep understanding of force, scientists have been progressing. Both Fermilab's Large Collider and Desy's electron-proton collider Hera provide world-class platforms for quantum chromodynamics and help us deepen our understanding of QCD. In particular, through cutting-edge topics such as the precise measurement of proton structure functions, the exploration of the origin of hadron spins, and the study of quark constraints, QCD has become the undisputed "strong interpreter" over the past 25 years, which, together with the theory of electromagnetism and electroweakness, constitutes the three pillars of contemporary particle physics.
The complexity and beauty of quantum chromodynamics lies in the fact that it paints an unparalleled picture of the universe with the most concise theories and parameters. From the microstructure of protons to the macroscopic motion of galaxies, the mystery dominated by quarks and gluons is explained here. With the continuous progress of theories and experiments, the future of science will further unravel the mystery of the world of quarks and gluons, let us wait and see.
In the world of quantum chromodynamics, the dance of quarks and gluons is so fascinating that they not only form the basic structure of matter, but also play out their stories in every corner of the universe. Quarks, the elementary particles inside these nuclei, attract or repel each other with their color charges, and gluons shuttle through them, transmitting powerful messages.
But the world of quarks and gluons is not static. In high-energy physics experiments, scientists accelerate them to near the speed of light through particle accelerators and then have them collide. In these collisions, quarks and gluons can transform into other particles, demonstrating the singularity and diversity of the quantum world. These experiments not only help us understand the basic composition of matter, but also reveal the state of the universe in the first few microseconds.
During these experiments, scientists have discovered many new particles, each with its own unique properties and effects. For example, mesons and baryons are composite particles made up of quarks that play a key role in the stability of matter and nuclear reactions. In addition, through the study of these particles, scientists have also discovered that there is a phenomenon known as "quark confinement" among quarks, that is, quarks never exist alone, they always appear in the form of hadrons.
Quantum chromodynamics is not just a theory about quarks and gluons. It also deals with the evolution of the universe, including the expansion and cooling of the post-universe and the formation of galaxies and black holes. This theory provides us with a framework for understanding the past, present, and future of the universe.
With the advancement of science and technology, especially the development of particle accelerator and detector technology, our understanding of quantum chromodynamics is also deepening. In the future, with more experimental data and theoretical research, we look forward to unlocking more secrets about quarks and gluons, and their role in the universe.
Through these explorations, we will not only be able to better understand the nature of matter, but also develop new technologies and materials that may have a revolutionary impact on fields such as energy, medicine, and industry. The study of quantum chromodynamics is a microcosm of the continuous progress of science, which shows that mankind's exploration of the deep-seated laws of nature is endless.