Quarks, gluons, vortex structures — all these strange words raise many questions among curious citizens. Why do physics accelerate particles and collide them at a high speed? What can we learn by observing how heavy nuclei form a cloud of quark-gluon plasma at the site of the collision? A recent experiment, conducted with the participation of Russian scientists, is on the cover of the Nature journal.
The international STAR collaboration with the participation of the National Research Nuclear University "MEPhI", Institute of High Energy Physics (Protvino) (NRC "Kurchatov Institute") and the Joint Institute for Nuclear Research (Dubna) for the first time has experimentally confirmed the vortex structure of the quark-gluon matter formed in collisions of heavy nuclei, and managed to study it. These results suggest that the matter of the early Universe was very hot and very fluid substance, where quantum vortices with extreme characteristics could exist.
But in order to understand what happened at the moment of the Big Bang in the evolving Universe with non-existent stars and planets, it is necessary to create conditions with characteristics that could come close to the first microseconds. For that end different countries create “corridors” for acceleration of particles, calling them accelerators. The largest such “corridor” has a circumference of 26.7 km and is called the Large Hadron Collider. As the explosion causes collision of particles, the colliders created the system that generates it.
The Relativistic Heavy Ion Collider (RHIC)
The experiment was conducted at the Relativistic Heavy Ion Collider (RHIC) located at the Brookhaven National laboratory, USA. Scientists took the nucleus of gold, because they are heavy and easy to be worked with.
It is very important for physicists to understand the mechanisms of formation of stars, planets, and us.
Observations have shown that matter behaves differently, sometimes quite suddenly in the macro - and micro-world. In fact, during the last 100 years, scientists are trying to break down the particles of matter into smaller components. Now they are inside the atomic nucleus. There are so-called quarks and gluons — the fundamental or elementary particles. At the moment elementary particles are the smallest at which we are able to break down matter.
Quarks (and gluons) have a charge of strong interaction, called a "color" (it has no relation to the usual color, it's just a name). Therefore quarks are usually depicted as colored (red, blue, green) balls for descriptive reasons.
Until the beginning of the XX century atoms were considered to be the fundamental particles. Then it turned out that there are atomic nucleus and the electron inside. Later it has been discovered that the atomic nucleus consists of protons and neutrons, which were considered to be fundamental particles. Now it has become clear that protons and neutrons consist of quarks.
Usually scientists draw 3 quarks (two “u” and one “d”) to visualize an internal structure of a proton, however, according to modern concepts, the structure of hadrons (particularly protons) is much more complicated.
Physicists also understood that not all the particles, which they had opened, are active "players" in a moment of strong interactions, for example in the interpenetration of matter in the time of the explosion. At the moment they managed to prove that exactly quarks and gluons and also composed of them particles called hadrons participate in a strong interaction. The “liberation” of quarks and gluons requires a huge temperature and energy that scientists want to recreate in the experiments.
Colliding beams of heavy nuclei are used for these purposes. Their collisions allow to form matter with a temperature of around 2-3 trillion degrees, which is about 100 thousand times higher than the temperature at the center of the Sun. Under such extreme conditions, protons and neutrons, called nucleons and which form the visible world, "melt", and the matter transform into a new state, where quarks and gluons are free at the nuclear scale. This is the quark-gluon plasma – a "soup" from which the beginnings of stars and planets were formed.
The artist has depicted the quark-gluon plasma
The achievement of our physicists is that they have achieved the quark-gluon plasma state and studied its structure. Both true fundamental quarks and gluons and particles with a complex structure are characterized by its own rotation or the so-called spin.
Can you imagine a liquid all the "drops" of which are rotating? It is probably a fantastic spectacle and was accompanying the first microseconds after the Big Bang!
Scientists from the National Research Nuclear University “MEPhI”, as well as their colleagues from the Institute of High Energy Physics (Protvino) (NRC "Kurchatov Institute") and the Joint Institute for Nuclear Research (Dubna) studied the magnitude of the vorticity of quark-gluon fluid, and found that the specified value was exceeds the vorticity of all currently known liquids by many orders of magnitude (for example, the recently measured vorticity of superfluid helium nanodrops is "only" 107 s-1, while the vorticity of quark-gluon fluid is around 1022 s-1).
A schematic picture of the registration of lambda hyperons in the STAR installation. The dashed line denotes the trajectory of the lambda hyperon flight. The decay of the lambda hyperon on the proton and pi-meson is indicated by white lines.
"These results are critical for further research, which on the one hand can provide substantial progress in the understanding of the complex interactions between quarks and gluons, on the other can open up new possibilities for an interdisciplinary approach for the study of liquids spintronics," said the Professor of Physics Department of MEPhI Vitaly Okorokov who participates in the STAR experiment as a part of the scientific group under the leadership of the MEPhI rector Mikhail Strikhanov.
Results of the STAR experiment indicate that quark-gluon matter, formed in the collisions of heavy nuclei, is not only the hottest and least viscous, but the most rotational liquid of all the known.
