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September 05 | Scientific Activity

Big Physics Week in Russia

One of the world's largest regular scientific forums was open on August, 31st in St. Petersburg. "Physics of the Large Hadron Collider" International Conference was held for the third time and was held for the first time in Russia. It lasted until September, 5th this year. At the first day of the forum Russian scientists and their Western European counterparts held a joint briefing where told about the cooperation between Russia and CERN, the recent launch of the LHC at full capacity and also commented on the recent work of ALICE collaboration, published on August, 17th in Nature Physics. 90 Russian researchers taking part in the collaboration are the co-authors of the article. The briefing was organized jointly by STRF.ru online edition, "Kurchatov Institute" Scientific Research Center Petersburg Nuclear Physics and the St. Petersburg State University.

After the discovery of the Higgs boson and two-year stop for modernizing the Large Hadron Collider (LHC) resumed its work in June, 2015. Energy of proton-proton collisions has reached the design capacity of 13 TeV for the first time since its inception – i.e. became approximately equal to the energy that the particles had after one billionth of a second from the beginning of the Big Bang. Scientists say that it will make possible to conduct a pilot test of bold hypotheses about the structure of space-time and to continue the search for new elementary particles that make up the basis of the dark matter of the Universe. According to Paolo Bagnoli from the University of Pisa, who spoke at the opening of the conference, the first data in the CMS experiment at energies of 13 TeV had already been received and would be used in the search for new physics – the physics beyond the Standard Model, which describes the interactions of all the currently known elementary particles. However, scientists continue to process the data obtained more than two years ago and publish important scientific results. One of such works – of the ALICE scientific collaboration – was published in the prestigious Nature Physics journal on August, 17th.

ALICE

Physicists like to say that they are "not too happy" with the results which are obtained from the Large Hadron Collider. Until now, all these results have confirmed the Standard Model set from the 1970s and have not solved the contradictions that could accumulate around it after and even before its creation (it is, for example, about the mysterious dark matter, which is three-quarters of all the mass in the Universe – as it was found out of gravitational observations in the early 1930s). Recent high-profile discoveries – the Higgs boson, the rare decay of Bs-meson into two muons – are from the same series of results that are conditionally "not welcomed". The experiment conducted by the ALICE collaboration, continued the "tradition". It concerns one of the most important problems of modern physics – the problem of dominance of matter over the antimatter in the foreseeable space. "The substance of the Universe that we see, it is the protons and light nuclei. Accordingly, we have observed asymmetry between the matter and antimatter, though according to the theory of the Big Bang there was a complete symmetry at the initial moment", – Victor Kim, Deputy head of the High Energy Physics Division of the "Kurchatov Institute" Scientific Research Center of the Petersburg Nuclear Physics Institute (PNPI), told. In other words, the nature was not to make any preference for one. This is a feature of so-called CPT-symmetry, which states that the laws of physics for a particle remain the same, if its charge is reversed, if it is flipped and reversed in time (in particular, it means that all properties of particles and antiparticles should be equal in magnitude – charge, mass, magnetic moment, and so forth).

Nevertheless, there is matter and there is almost no antimatter in the observable Universe, and this fundamental contradiction requires explanation. One of which may consist in the fact that the CPT-symmetry is not really an absolute law. In this case, the existing basic laws of physics will have to be reсonsidered.

The data of ALICE collaborations, published in Nature Physics, confirm that CPT-symmetry is preserved. This narrows the number of possible explanations of why matter prevails over antimatter. That is you need to look for some factors not related to intrinsic properties of matter and antimatter to explain why the first one dominates over the second on. "There are bold theories that can be closed; that is the symmetry between matter and antimatter stays. <...> Everything we need to explain can be explained only in a conservative manner", – Victor Kim explained the conclusions to which the research of ALICE collaboration leads. The special novelty of the work lies in the facts that in the ALICE collaboration the CPT-symmetry has been confirmed with the "real" matter – the nuclei of helium-3 and antihelium-3, – as well as accuracy of CPT-symmetry for the nuclei of deuterium has been 100-fold increased compared with 50 -year-old experiments. It has made possible to understand:

there are no differences not only between particles and antiparticles, but also between their interaction inside the nucleus, and thus the matter and the antimatter are completely symmetrical.

Petersburg Nuclear Physics Institute was behind the ALICE experiment and the ideas of the scientists of the Institute, inherent in it, continue to work, Alexei Vorobyov, the Head of the High Energy Physics Division of the "Kurchatov Institute" Institute Research Center of the Petersburg Nuclear Physics, told. PNPI suggested the idea of muon spectrometer for the ALICE experiment, subsequently implemented in conjunction with other scientific groups. In addition, scientists of the Institute are engaged in the analyzing and processing of data, he explained the Institute's contribution to the work of collaboration.

"In 1992, when there was no the Large Hadron Collider, the ideas developed in St. Petersburg went as basic ones for the ALICE collaboration, which is engaged in the quark-gluon plasma experiments", – Gregory Feofilov, the Head of the St. Petersburg University group in the ALICE experiment , co-author of the publication in the Nature Physics, agreed. - Engineering and scientific potential of St. Petersburg made it possible to develop such proposals, which have been brainstormed since 1992 and are now working at ALICE installations. St. Petersburg State University is currently involved in the project of modernization [of this facility], which is based on the latest detectors. Some of these detectors are to test in the university; students of St. Petersburg State University have begun working with them". Feofilov also added that the most important contribution of St. Petersburg State University in ALICE is a theoretical school: it determines the physical search, which involves students, graduate students and researchers, and without which "just a detector would be needed by very few people".

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