International experts discussed NICA Project

News, 19 December 2022

An international online seminar on methods of data analysis and processing in experiments at the NICA Accelerator Complex (NICA-2022) was held on 13–15 December 2022 organized jointly by NRNU MEPhI and JINR.

The event is unique in its format since it brought together theoreticians and experimentalists involved in the data analysis and in the preparation of new experiments, namely BM@N (“Baryonic Matter at the Nuclotron”) and MPD (“Multipurpose Detector”) at the NICA Accelerator Complex.

Group photo of part of meeting participants

The main scientific goal of these experiments is to study the phase diagram of highly compressed baryonic matter under laboratory conditions. In nature, such matter is formed only in mergers of neutron stars or as a result of a supernova explosion. More than 100 scientists from Bulgaria, Brazil, Israel, China, Mexico, Russia, the USA took part in the seminar, including experimentalists from international collaborations: BM@N (NICA), MPD (NICA), NA61/SHINE (CERN), STAR (BNL), and ALICE (CERN) and theoreticians from the Laboratory of Theoretical Physics JINR and other scientific centres.

The seminar programme included reports on the following topics: 1. Phase transitions in quantum chromodynamics and the equation of state of hot nuclear matter; 2. Hydrodynamics, flows and polarisation of particles born in nuclear collisions; 3. Birth of strangeness, clusters, and hypernuclei; 4. Direct photons and dileptons.

Slide from Shi Shusu’s report

So, Victor Braguta (JINR) spoke about the principles of studying phase transitions in quantum chromodynamics by means of calculations on space-time lattices. A general review of phase transitions in various systems was given by Dmitry Voskresensky (JINR, MEPhI), who emphasised that the properties of particles that constitute dense strongly-interacting systems can differ significantly from their properties in vacuum. Various principles for constructing the equation of state for matter formed in heavy ion collisions were presented by Evgeny Kolomeitsev (JINR). Giorgio Torrieri (Brazil) enthusiastically spoke about the principles underlying the hydrodynamic approach to the description of nucleus-nucleus collisions. New results of the STAR experiment obtained within the energy scanning programme at the RHIC collider were presented by Shi Shusu (China). It was argued that new data obtained in collisions at energies of sNN =3 GeV could provide new information about the properties of nuclear matter and its equation of state. An interesting report was made on the possibility of using data on azimuthal collective flow of particles to study the microscopic structure of colliding nuclei. The thirty-three-year history of research of elliptical particle flows was colorfully illustrated in the report by Arkady Taranenko (MEPhI). Plans for future experiments with the production of charmed particles in the ALICE experiment at the LHC accelerator were presented in the report by Yuri Kharlov (IHEP NRC KI).

Slide from Alexander Zinchenko’s report

The possibility of observing the production of nuclear clusters and hypernuclei in collisions at energies achievable at NICA was discussed in the report by Viktor Kireev (JINR), and the theoretical calculations performed in the framework of the hydrodynamic approach were presented by Marina Kozhevnikova (JINR). The report by Alexander Zinchenko (JINR) was devoted to the proposed study of the strange particle production in the MPD experiment. The latest data on the kaon and pion production obtained in the BM@N experiment were vividly discussed by participants during and after the presentation by Vasily Plotnikov (JINR). Mikhail Mamaev (MEPhI) analysed the possibilities of measuring collective proton fluxes in the BM@N experiment. Coincidentally, during the days of the seminar, the BM@N experiment began its first experiment on the study of collisions of heavy xenon nuclei (Xe) with a cesium iodide Cs(I) target. Oleg Rogachevsky (JINR) spoke about the studies of two-particle correlations in collisions at the energies of the NICA Complex.

Slide from Itzhak Tserruya’s report

Itzhak Tserruya (Israel) gave an overview of possible experimental manifestations of chiral symmetry restoration in dense and hot strongly interacting matter in the photon production, and Dmitry Peresunko (NRC KI) presented the experimental status of observing the production of photons and dileptons in nuclear collisions. The theoretical report by Alexei Larionov (JINR) was devoted to the same topic.

Slide from Subhash Singha’s report

Six reports on the second day of the workshop were devoted to the topic of spin polarisation of hyperons and vector mesons produced in collisions of unpolarised nuclei. Subhash Singha (China) reported on the status of hyperon polarisation measurements carried out in experiments at the RHIC complex, and Victor Ryabov, Head of the MPD collaboration (PNPI NRC KI, JINR), spoke about vector-meson polarisation measurements. Elizaveta Nazarova (JINR) presented a new programme for determining the polarisation of hyperons using the MPD experiment. As argued in the report by Vadim Voronyuk (JINR), the polarisation of hyperons is associated with the vorticity of nuclear matter arising from the collision of nuclei, which is concentrated in the form of two vortex rings. The possibility of experimental verification of such a picture was discussed in the report by Yuri Ivanov (JINR, MEPhI). An alternative approach to understanding the appearance of hyperon polarisation was proposed by Alejandro Ayala (Mexico).

Slide from Vadim Voronyuk’s report

The computer support of experiments at the Nuclotron-NICA Accelerator Complex also received attention; reports by Dmitry Podgainy (JINR) and Igor Pelevanyuk (JINR) were devoted to this topic.

At the end of each day, a special time was allocated for additional discussion. During the presentations, each participant could ask additional questions in the chat, which were collected by moderators of the seminar into one document. The seminar finished only when answers to all questions were received.

The publication of seminar proceedings is planned in the journal MDPI Particles. According to most participants, the seminar was very successful and can be considered the main international seminar on relativistic nuclear physics, which took place in Russia in 2022. It was decided to organize a similar seminar in 2023.