Quark-gluon plasma - computer model
Quark-gluon plasma is a state of matter in which the latter is a set of gluons, quarks and antiquarks. The formation of such a plasma proceeds similarly to the formation of ordinary plasma.
Atoms of ordinary matter are mostly neutral, since the charge of their nucleus is compensated by an electron rotating around the nucleus. As the temperature rises, the atoms ionize, that is, the electron gains enough energy to leave its orbit, resulting in a separate positively charged nucleus and a negatively charged electron. This state of matter is called plasma.
In the case of quark-gluon plasma, the so-called “color” is compensated. Color is one of the characteristics of quarks that make up a particle - a hadron, and gluons - that “stick together” quarks (they are carriers of strong interaction).
Confinement
Quarks and gluons, which make up hadrons, are not capable of being in a free state under normal conditions. So, if you try to "pull" them to a distance greater than the size of the hadron (10 -13 cm), the energy of quarks and gluons increases rapidly and indefinitely. The phenomenon of the impossibility of separating quarks is called "confinement", which is translated from English as "imprisonment". This phenomenon is described using the previously mentioned characteristic - color. Thus, in a free state, only objects that are composed of quarks and have a white color can exist. For example, the proton is made up of quarks whose colors are green, blue, and red, which add up to white.
However, there are conditions under which confinement works differently. These conditions include ultra-low temperature or ultra-high pressure. In the case of such conditions, the wave functions of two nucleons (the common name for protons and neutrons that make up the nucleus of an atom) overlap, in simple terms - these particles, as it were, "leap on top of each other." As a result, quarks cease to distinguish their native nucleons and begin to move freely throughout the entire volume of the nucleus, which consists of these nucleons. Thus, confinement takes place, but the volume of its “prison cell” increases many times. Therefore, the more nucleons touch and “overlap”, the larger the size of the “cell”. Such a phenomenon can reach macroscopic scales and more.
Existence and receiving
Quark-gluon plasma arises as a result of the “imposition” of many nucleons on top of each other, as a result of which quarks move freely within the volume of the nucleus, which consists of these nucleons. Such a plasma exists primarily under conditions of increased pressure, as, for example, in the cores of neutron stars. However, in 2005, American scientists managed to obtain quark-gluon plasma at the RHIC heavy ion collider. At this accelerator, it was possible to push the nuclei at a speed of 99.99% of the speed of light, as a result of the collision, 20,000 GeV of energy were released, a pressure of 10 25 -10 30 atmospheric pressure was reached and a temperature of 10 9 -10 10 K. Later, a similar experiment was repeated at the Large Hadron Collider at CERN at high energies.
- How did you get into science?
Astghik Torosyan, Software Engineer, Information Technology Laboratory:
It all started with a love of mathematics. As you know, in theoretical physics there is a lot of mathematics (if not all). After school, the question arose of choosing a profession, then it was "fashionable" to go to economists; I have always liked the exact sciences, in particular mathematics, and I also decided to follow this path. However, later I entered the Department of Applied Mathematics and Informatics, and two years later I moved to the Department of Theoretical Physics. Work on qubits (a qubit, or quantum bit, a unit of quantum information) was suggested by my thesis supervisor, and after graduating from the university, I joined him at the Joint Institute for Nuclear Research. This is where my journey began.
Maria Fomina, Junior Researcher, Laboratory of Nuclear Problems:
At school, mathematics and physics were always easy for me. Therefore, when it came time to choose a profession, I knew for sure that it would be connected with the exact sciences. I chose the Faculty of Physics of the Voronezh State University. When it was necessary to choose a narrower specialty, I decided that medical physics, namely the use of nuclear physics in medicine, would suit me quite well - both interesting and suitable for a girl. She completed her bachelor's degree in this specialty, but entered the master's program in the specialty "nuclear physics". In the first year of the master's program, I was offered to go to Dubna, first for an internship, and then for a diploma. Which is what I did. It was in Dubna that I connected my life with the most interesting, mysterious and widespread particle on Earth - the neutrino.
Alexandra Friesen, Junior Researcher, Laboratory of Theoretical Physics:
It seems to me that coming into science is always accidental, in fact. First you learn. I studied physics at Saratov University. I had a specialty - the dynamics of nonlinear systems. Oscillations, waves, radiophysics. By the third course, I just realized that I was tired of doing this. Because everything is the same, but under a different sauce. And we just started teaching a course in theoretical physics. I went to the Department of Theoretical Physics and said: “Take me to you!” And then I came to Dubna for a conference and decided to stay. I definitely had no plans to do science in my third year. I had plans up to and including leaving and doing something else. So it happened by accident. I have been in Dubna since my fifth year, that is, since 2006. First, I liked the city. Secondly, I liked the institute. And thirdly, something really touched me in the sense that it became interesting. Although, of course, it was not quite “take me to your place”. I came to the conference. At such events, especially at summer schools for young scientists, sometimes the professors themselves come up and engage in self-promotion. At our department in Saratov, everyone knew this and advised me to take a closer look there. So I found a supervisor.
You know, in the XVII-XVIII centuries. there were such specially trained people who got people drunk, and then those who got drunk suddenly woke up as sailors on ships. These conferences were held in much the same way. What's happening? Lightly drink, and wake up already on the ship!
- What is the subject of your scientific work?
A. Torosyan:
Do you know what a qubit is - a quantum bit? Here I am engaged in the theory of quantum computing. We consider quantum mechanical systems (two qubits and a qubit-qutrit pair) that can be described by a density matrix. Having the density matrix in hand, one can investigate the properties of the listed systems, find the conditions for separability (or entanglement), measure the degree of entanglement, classify the orbits of the corresponding groups in accordance with the degenerations of the density matrix, and much more.
M. Fomina:
I am an experimental physicist, I am currently working on the DANSS experiment, which is taking place at the Kalinin NPP. This experiment solves two problems at once: fundamental - to better understand the nature of neutrinos, and applied - to use neutrinos to monitor the safety of nuclear power plants.
The neutrino is the most common particle in the Universe, but at the same time it is one of the most poorly understood: it has no charge, which means it does not participate in electromagnetic interactions and is not part of the matter surrounding us. Until now, it has not been possible to measure its mass - there are only limitations. There is another interesting phenomenon associated with neutrinos - neutrino oscillations. What it is? There are three types of neutrinos - electron, muon and tau neutrinos. These are different particles with different masses, but with free movement they can turn into each other, that is, if a muon neutrino flies from the source, then when moving away from it, one can already observe an electron or tau neutrino. Just for the discovery of neutrino oscillations, which prove the presence of mass in a particle, the Nobel Prize in Physics was awarded in 2015 (according to the Standard Model, the neutrino has no mass).
The most powerful source of neutrinos on Earth are nuclear power plants. During the burnup of nuclear fuel (mainly uranium), a huge amount of reactor neutrinos (to be precise, electron antineutrinos) is formed, while weapons-grade plutonium is produced. And each neutrino carries some information about what happened in the reactor, because the energy of the neutrino directly depends on how the fuel burns out, what elements are burned there at the moment, what is the power of the reactor. Accordingly, knowing the so-called energy spectrum of these particles, we can say that at the moment our fuel consists of such and such an amount of uranium, such and such an amount of plutonium, which has already been accumulated. You can also say what is the thermal power of the reactor at the moment.
However, this is just words. First, as I said, neutrinos are difficult to detect. Secondly, nuclear power plants are closed objects, and for such monitoring, the detector must be placed close to the reactor - a few meters away. And the detector is the so-called scintillation liquid, and it is combustible, plus you need a lot of it - these are giant detectors. Therefore, in practice, such monitoring did not work before.
We work directly at the reactor of the Kalinin NPP, and we have a scintillator, not liquid, but solid - polystyrene, and our device is compact. That is, it is a cubic meter of plastic - that's the whole detector. If we put three such cubes around the active zone (the reactor is a large cylinder about three meters in diameter and the same number in height), then we can get its “tomography”: with an accuracy of 10-15 cm, understand where uranium burns out faster, where how much plutonium, where what temperature. This will not only improve safety, but also optimize operation. And this is money.
Reactor core monitoring is an applied task of our detector. But there is also a fundamental (and for me as a physicist more interesting) task - the search for short-range neutrino oscillations into the fourth type of neutrino - sterile. Many of the experiments that were done to study reactor neutrinos showed a shortage of particles, that is, the detectors registered fewer particles than expected. This phenomenon is called the "reactor antineutrino anomaly". One of the explanations for this deficit is the possibility of the existence of the fourth type of neutrino - sterile. It is the search for oscillations in this state that is the fundamental task of our detector. The DANSS detector has been operating since 2016, now statistics are being collected. That is, if they are, we can see it. If they are not, we will see it too. After all, it is so difficult to measure neutrinos that there is a possibility that they were simply missed on other detectors, and we will measure more precisely - our detector is located only 11 meters from the reactor core, and in general, we will not see any deficit, anomalies. Proving or refuting something new is always interesting, at least. After all, it is very cool to consider yourself involved in some kind of “new” physics.
A. Friesen:
What am I doing now? I'll explain now. There are two ways in which mass is formed in the universe. The first mechanism is at the most elementary level: initially massless elementary particles become massive through the Higgs mechanism. Therefore, all the particles that make up the Standard Model have mass. And in fact, this fact greatly violates the global symmetry in the Universe. Nature did not stop there and did not put all the eggs in one basket. Quarks begin to interact with each other to form hadrons. And it turns out that this interaction acquires mass. This is the second mechanism. That is, there was a 5 MeV quark, it began to interact with its neighbors and began to weigh 300 MeV. And this strongly interacting quark, located inside the proton, cannot be pulled out of the proton - there is such a rule. And naturally, probably, scientists had an idea: how can these quarks be obtained and can they even be free? Then we do a thought experiment: we begin to compress the core. The nucleus is made up of protons and neutrons, which in turn are made up of quarks and gluons. If we compress it, protons and neutrons begin to overlap with each other. They overlap, and it becomes unclear which quark belongs to which nucleon. And they say about such a state that a phase transition has occurred, that is, the quarks have been released. This state is called quark-gluon plasma, and it is assumed that all of our matter was in this state immediately after the Big Bang.
Supposed. But this quark-gluon plasma still causes a lot of controversy among scientists. In order to find it, experiments are being carried out, for example, at the LHC, and in Dubna they will be carried out at the NICA collider. And I am engaged - in a theoretical sense - in the search for a phase transition from the state of hadronic matter, familiar to us, to the state of quark-gluon plasma. It is assumed that there must be a phase transition. And in fact, perhaps even two types of phase transitions: very soft, when quarks can coexist with hadrons, and hard, when at first there were only hadrons, and then immediately quarks and gluons. But you need to understand that these processes are not at all similar to what we imagine in our ordinary, large and classical (in the sense of not micro- and not quantum) world. Quark-gluon plasma existed for only 0.1 seconds after the Big Bang and in a very limited volume. And then the transition happened. We are developing a model of how it could have happened. Very limited scope. Extremely limited amount of time. Then immediately the expansion of this matter begins to take place. Cooling begins, and we no longer see these free quarks. We already see them in hadrons, pions (π-mesons), resonances and kaons (K-mesons), but in anything! And here the most interesting thing is precisely in finding and understanding whether this state of the quark-gluon plasma, the release of quarks and gluons, is possible or not.
- What are your plans for the future?
A. Torosyan:
I would like to continue working in this area; I enjoy doing analytical as well as numerical calculations using computer algebra systems. We draw multidimensional objects, calculate entanglement probabilities, get new formulas and come to beautiful conclusions. I love being a part of it all.
M. Fomina:
In short, my plans for the future are science, science and science. I can no longer imagine myself in another direction of physics, not to mention other specialties. Neutrino physics is now very relevant all over the world. Physics does not have to think about another section at all. Therefore, it is very important for me to continue participating in the DANSS experiment and defend my Ph.D. thesis - these are the most important plans for the near future.
A. Friesen:
Complex issue. I probably have an interest in astrophysics. There is such an object as neutron stars, which suggest that inside them the matter can be in the state of quark-gluon plasma. Because they are very small, compact and hot objects. Interested in black holes. Maybe I'll do that in addition. Because they are overlapping areas. And a person who studies neutron stars makes very extensive use of the model that I am working on.
In the suburbs of Geneva, Switzerland, hidden behind flowering meadows is a warehouse with an elevator that only goes down. At a depth of hundreds of meters, inside an octagonal hollow tube resembling a large barn, there are hypercomplex detectors that detect proton collisions. Scientists involved in the experiment at the LHC decided to get a strange substance that most likely filled the newborn Universe a moment after the Big Bang. The so-called quark-gluon plasma was created in the laboratory and before that, by the collision of relatively large lead atoms. This time, the researchers decided to push together negligible protons, and then not all of them.
The importance of the results of the study, published recently in the journal Nature Physics, will not immediately become clear to the average person. Basically, the use of protons will provide a more accurate way to analyze the quark-gluon plasma. According to researcher Livio Bianchi, proton-proton collisions will avoid getting a lot of unnecessary, chaotic data, which will take too long to analyze. The discovery will also allow physicists to study the mechanism of proton collisions and, perhaps in the future, thanks to this, discover other particles that are still unknown to science, as happened with the Higgs boson.
All protons and neutrons are made up of two kinds of quarks, elementary particles, but in addition to them there are four more kinds (or "flavors"), and as a result of the combination of all six varieties of these particles, a huge variety of larger particles is obtained. The glue-like particles, gluons, hold the quarks together, usually in pairs or triplets, and so it's almost impossible to find a single quark, because the attractive force between them increases with distance, rather than weakening. However, it is enough to apply energy to them, and the quarks turn into a "hot soup", where they are all tightly bound like an ideal liquid. This is the quark-gluon plasma that scientists are so interested in.
Scientists working at the collider knew about the existence of this quantum soup from experiments on high-energy collisions of gold or lead atoms, which were carried out at the US collider RHIC and LHC. But in order to actually announce the discovery of this substance, they needed to get a few things. In particular, they needed a sphere of liquid plasma heated to a trillion degrees, since under such conditions the property of quarks, known as “strangeness enhancement”, allows the particle streams to be divided into singlets, that is, the scientists would get single quarks at the output. But how to carry out such an operation?
The CERN researchers achieved the aforementioned state by comparing the yield of exotic kaons and lambda particles (each containing one kind of quark, the “strange” quark), the xi particle (which contains two such quarks), and the omega particle (which contains three) from proton collisions. Accordingly, the more strange quarks, the greater the yield. During the collision of protons, particles of different sizes are formed, and more particles at the exit would mean an increased proportion of strange quarks in them.
The ALICE detector, designed specifically to detect such microscopic operations, does its job well thanks to a complex array of detectors placed under a protective shell. Such work may seem highly speculative, and it is true: scientists do not claim that they have already detected quark-gluon plasma as a result of proton-proton collisions. Regardless, ALICE and other CERN CMS and ATLAS detectors bring together hundreds of physicists looking for similar results. This week, the proton collision experiment was run at only half the power that the LHC is capable of. The LHC has finally returned to work after many months of technical work, which means that the experiment will continue and the study of elementary particles will resume in the near future.
It's only been three weeks since work began on heavy-ion collisions at the Large Hadron Collider, and physicists from three experiments (ALICE, CMS and ATLAS) have already received the first data on what matter was like in the earliest moments of the universe. The ALICE experiment (A Large Ion Collider Experiment), specially optimized for the study of heavy ions (beams of lead ions are now colliding), has already published the first data indicating the formation of the so-called quark-gluon plasma.
This is the state that all matter was in about 0.00000000001 seconds after the Big Bang.
At that moment, even elementary particles - protons and neutrons - had not yet "assembled" from their constituent quarks and gluons. Their temperature and velocities were too high for the formation of particles, so they were only a mixed "liquid" - quark-gluon plasma. ALICE was able to observe the so-called elliptical flow, which directly speaks of the emergence of quark-gluon plasma.
A few days ago, the ATLAS and CMS collaborations reported the discovery of another effect characteristic of the formation of this extreme state of matter - the quenching of hadron jets. The work of ATLAS physicists accepted for publication in the journal Physical Review Letters, a
On Thursday, CERN will host a seminar where all the latest results of the collaborations will be presented.
“It is truly impressive how quickly the experiments arrived at these complex physical results. Collaborations compete with each other in the speed of publication of material, but, of course, work together to create a complete picture of the phenomena studied and to cross-compare the results. This is a great example of how competition and collaboration work - the key points in this area of \u200b\u200bresearch, ”said Sergio Bertolucci, CERN Director of Research, quoted by press service of the organization.
LHC experiments basically study the same phenomena, but their designs are fundamentally different.
This makes it possible to observe the events occurring during the collision of particle beams by different methods, to register them more clearly and to check whether the observation is a consequence of the occurrence of some effect or is it just “noise”. Only when the same data are obtained by several methods, they are considered reliable.
The study of quark-gluon plasma is one of the LHC's priorities. This will help not only to understand what the Universe looked like immediately after its birth, but also to study the process of formation of modern matter.
Quark-gluon plasma is the most "distributed" state of matter, where particles - quarks and gluons - are not bound by the so-called strong interactions, which now support the existence of protons, neutrons and, in general, all the nuclei of the Mendeleev Periodic System that make up our world - living and inanimate.
By studying quark-gluon plasmas, scientists hope to better understand the nature of the strong force.
How is this unprecedented state created in the LHC? In the collision of lead ions - very heavy particles (they are about 200 times heavier than protons) - enough energy is concentrated at the intersection point of the beams to create "microdroplets" of "primordial" matter in a very small volume. Its presence is registered by a number of special signals that can be measured by the equipment of the LHC detectors.
The ALICE collaboration paper states that hot quark-gluon plasma behaves like a very low viscosity fluid (ideally fluid). These data are consistent with those obtained earlier at the RHIC collider (The Relativistic Heavy Ion Collider, Brookhaven National Laboratory, New York).
“Now that we've started pushing heavy nuclei together, the LHC has become a real 'Big Bang device' — that sounds like science fiction. Our observations of quark-gluon plasma confirm the data of colleagues from RHIC, but we can already note additional important features,” said Jurgen Shoecraft, head of the ALICE collaboration.
The ATLAS and CMS experiments have effectively observed jet quenching, as their systems allow for very efficient "sealing" of energy and measuring its release. They measure, in particular, jets of particles arising from collisions. The jets produced by proton collisions most often appear in pairs.
However, when heavy ions collide, the jets interact under harsh conditions of a hot, very dense medium.
The result is a very characteristic signal, known as jet quenching, which is expressed in a sharp drop in their energy. This means that when particles collide in the detector, a medium is created that is much denser than any known matter. Jet quenching is a good parameter for a detailed study of plasma behavior.
The collision of lead beams in the LHC will continue until December 6th. The collider will then be shut down for several months.
The Large Hadron Collider is the largest and most powerful particle accelerator in the world. It is located underground in a 27-kilometer tunnel in Switzerland and France near Geneva at the European Center for Nuclear Research (CERN). The active phase of the collider began at the end of May 2010. The four detectors of the giant instrument (CMS, ATLAS, ALICE and LHCb) are studying the state of matter in the Universe immediately after the Big Bang, searching for the Higgs boson - the particle that gives rise to mass in the Universe, as well as searching for "new physics" - phenomena beyond the Standard Model , the dominant modern theory of particle physics.
QUARK-GLUON PLASMA, a hypothetical state of strongly interacting matter characterized by the absence of color confinement (confinement). In this state, colored quarks and gluons captured by hadrons are released and can propagate as quasi-free particles throughout the entire volume of the quark-gluon plasma - “color conductivity” appears (similar to electrical conductivity in ordinary electron-ion plasma). According to modern concepts, this state is formed at high temperatures and/or high baryon densities of equilibrium hadronic matter.
Under natural conditions, the quark-gluon plasma apparently existed only in the first 10 -5 s after the Big Bang. It is possible that it can also be present in the center of the most massive neutron stars. There are reasons to believe that atomic nuclei in their composition, in addition to protons and neutrons, contain "droplets" of quark-gluon plasma, i.e. nuclei are considered as heterophase systems.
The possibility of the existence of a quark-gluon plasma is closely related to the spontaneous symmetry breaking of the physical vacuum in quantum chromodynamics (QCD) and to asymptotic freedom - a decrease in the effective color charge with a decrease in the distance between colored particles, with an increase in temperature and/or density. However, there is still no rigorous mathematical proof of the existence of a phase transition and color confinement in QCD. Significant progress towards solving these complex problems has been achieved in computer calculations on a spatial lattice (see Lattice field theories).
For experimental studies of quark-gluon plasma, it is proposed to create the necessary conditions for its formation in the laboratory by the collision of high-energy heavy nuclei. Estimates show that the system formed in the nuclear collision region will exist for a sufficiently long time, its energy and compression can ensure the achievement of the quark-gluon plasma phase when using already operating heavy ion accelerators. The processes of lepton pair production, photon emission, and an anomalously large number of strange particle productions are supposed to be used as the most important signals providing information on the formation of a quark-gluon plasma.
Lit.: Shelest V. P., Zinoviev G. M., Miranskii V. A. Models of strongly interacting elementary particles. M., 1976. T. 2; Gorenshtein M. I. et al. Exactly solvable model of phase transition between hadron and quark-gluon matter // Theoretical and Mathematical Physics. 1982. V. 52. No. 3; Feinberg EL Thermodynamic fireballs // Uspekhi fizicheskikh nauk. 1983. V. 139. No. 1.
