PNPI project leader:    V.G.Ryabov

The NICA (Nuclotron-based Ion Collider fAcility) project is one of the mega-science projects in the Russian Federation that is currently under construction at JINR, Dubna. The NICA complex consists of a heavy-ion collider and several experimental facilities. One of the facilities is the fixed-target BM@N (Baryonic Matter at Nuclotron) experiment which is designed to study heavy-ion collisions in the energy range up to vsNN = 3 GeV. Two other facilities are at NICA collider: the MPD (Multi-Purpose Detector) experiment to study the relativistic heavy-ion collisions in the energy range vsNN = 4-11 GeV and the SPD (Spin Physics Detector) experiment to study collisions of polarized beams of protons and deuterium in the energy range up to vsNN = 27 GeV.
       Historically, the study of heavy-ion collisions with beams began at low energies of ~ 1 GeV at the Bevalac accelerator (USA), then continued at energies of ~ 5 GeV and ~ 20 GeV at the AGS (USA) and SPS (CERN) synchrotrons. Significant progress has been reached in the transition from fixed-target experiments to colliders. The first heavy-ion collider in the world was RHIC (USA), which made it possible to increase the nuclear interaction energy up to 200 GeV and experimentally discover a new state of a strongly interacting matter - quark-gluon plasma (QGP). Further experiments at the LHC collider (CERN) at even higher interaction energies up to 5 TeV confirmed the discoveries made at RHIC. Experiments at top RHIC and LHC energies studied the phase diagram of the strongly interacting matter in the regime of high temperatures and zero baryon chemical potentials, lots of novel experimental methods and observances have been developed for the study. According to theoretical predictions, at high baryon densities and moderate temperatures, a first-order phase transition to a plasma state should occur, which ends with a critical point. This region of the phase diagram is poorly constrained. The high baryon densities can be probed by reducing the interaction energy of the nuclei. It is predicted that the maximum baryon density will be reached in interactions of heavy nuclei at vsNN = 5-10 GeV. This exact energy range will be covered by the NICA accelerator. Similar research programs are currently being implemented within the beam energy scan programs at RHIC and SPS, at SIS (Germany) as well as in the Compressed Baryonic Matter (CBM) experiment at the FAIR facility (Germany). A distinctive feature of the MPD experiment at NICA collider is the ability to accumulate larger data samples in comparison with other experiments, which can allow for more differentiated and accurate measurements of the predicted signatures of the phase transition. As a collider experiment, the MPD detector also has a large and symmetrical acceptance, which is advantageous for the study of fluctuations and flow observables.
       For PNPI, participation in the NICA-MPD project is a logical continuation of the experimental program carried out in the PHENIX and ALICE experiments at RHIC and the LHC colliders, respectively. PNPI employees have developed, created and delivered to Dubna a unique gas system for the main tracking detector of the MPD experiment - a time-projection chamber (TPC) with an active volume of ~ 20 m3. The employees are also involved in the development of algorithms and reconstruction software for the electromagnetic calorimeter (ECAL), development of analysis techniques and feasibility studies for various physical phenomena such as the production of short-lived resonances, direct photons, dilepton continuum, identified hadrons and vector mesons in various colliding systems. In addition, theoretical studies on the components of the small size of the nucleon wave function to reveal the effect of transparency of nuclear matter in the kinematics of proton-nucleon collisions at energies of the NICA accelerator are ongoing. In the future, PNPI will take part in the operation of the detector and the physical analysis of experimental data. An important contribution can become the participation in the upgrade of the experimental setup.
       (More information please see the presentation "NICA: Nuclotron-based Ion Collider Facility" (PNPI).
( http://hepd.pnpi.nrcki.ru/hepd/events/meetings/sessiya_2019/dec26/Nica_RiabovVG.pdf )

       About the participation of PNPI HEPD in the MPD experiment at the NICA collider, see the presentations from the winter session of HEPD 2022:    "Status of the MPD-NICA experiment" (V.Riabov, RNPL of HEPD).
"Participation of HEEP in the MPD-NICA experiment" (M.Malaev, RNPL of HEPD).