Physics of Particles and Nuclei最新文献

Obtaining quality physics results requires high-statistics data with low background contamination. The task of maximizing the signal as well as accurate estimation of combinatorial background is especially important at the start-up of the experiment when the amount of data is rather limited. The Multi-Purpose Detector (MPD) experiment at the NICA collider will have to deal with such issues in its first run. In this article, the task of reconstructing lambda hyperons with their weak decay into a proton and a negative pion using Monte Carlo simulated event samples of heavy-ion collisions is considered. Two approaches for evaluating the combinatorial background in the invariant mass spectra of decay products are studied: like-sign pair combinations and event mixing. Background-subtracted and efficiency-corrected hyperon distributions are presented, demonstrating performance of the MPD experiment in the future collider run.

The article presents a review of the results of studies of the unstable states in the relativistic dissociation of nuclei ¹⁰B, ^11,12C, ¹⁶O, ²²Ne, ²⁸Si, ⁸⁴Kr, and ¹⁹⁷Au in the energy range from hundreds of MeV/nucleon to several tens of GeV/nucleon using the nuclear track method. A systematic study of the fragmentation of incident nuclei with multiple production of the lightest fragments of He and H made it possible to study the dynamics of the manifestation of unstable nuclear states of ⁸Be, the Hoyle state, and the 4α-particle state of the ¹⁶O nucleus above the threshold in the relativistic dissociation of nuclei thanks to precision measurements of fragment outgoing angles. It is shown that, to reconstruct the relativistic decays of unstable nuclei in a nuclear photographic emulsion, it is sufficient to determine the invariant mass of the system of He and H fragments in the approximation of conservation of momentum per nucleon of the parent nucleus. This approach makes it possible to search for more complex nuclear states. An indication was obtained of an increase in the probability of detecting ⁸Be with an increase in the number of relativistic α particles in the event.

Based on the general form of the first correction to the result of current algebra for the masses of pseudoscalar mesons, we obtain a number of sum rules relating the masses of pseudoscalars to the light quark mass ratios ({{{{m}_{u}}} mathord{left/ {vphantom {{{{m}_{u}}} {{{m}_{d}}}}} right. kern-0em} {{{m}_{d}}}}), ({{{{m}_{s}}} mathord{left/ {vphantom {{{{m}_{s}}} {{{m}_{d}}}}} right. kern-0em} {{{m}_{d}}}}). A more careful consideration involving experimental data on (eta to 3pi ) decays allows us to identify a domain in which the results of these sum rules do not contradict each other. This determines the range of acceptable values for the ratios ({{{{{{m}_{u}}} mathord{left/ {vphantom {{{{m}_{u}}} {{{m}_{d}}}}} right. kern-0em} {{{m}_{d}}}}} mathord{left/ {vphantom {{{{{{m}_{u}}} mathord{left/ {vphantom {{{{m}_{u}}} {{{m}_{d}}}}} right. kern-0em} {{{m}_{d}}}}} {{{m}_{s}}}}} right. kern-0em} {{{m}_{s}}}}). Finally, the results are compared with known phenomenological data and calculation results on a lattice.

Two-pion interferometry provides access to the spatial and temporal size, shape, and evolution of the sources created in heavy ion collisions, offering strong constraints for theoretical models. In these proceedings, we will report the measurement of correlation strength ((lambda )) and femtoscopic radii (({{R}_{{{text{out}}}}}), ({{R}_{{{text{side}}}}}), ({{R}_{{{text{long}}}}}), (R_{{{text{out}} - {text{long}}}}^{2})) extracted from the two-pion correlation function in Au + Au collisions at (sqrt {{{s}_{{NN}}}} ) = 3, 3.2, 3.5, and 3.9 GeV. The dependences of these parameters on pair transverse momentum, pair rapidity, collision centrality, and collision energy will be presented, and their physics implications will be discussed.

The detector for tuning the beam convergence at the interaction point of the MPD (Multi-Purpose Detector) experiment at the NICA collider (Nuclotron-based Ion Collider fAcility) is discussed. The calibration procedure of the luminosity detector for determination of the absolute luminosity in the MPD interaction zone is presented.

Abstract

Recently, a large amount of experimental data has been collected in high energy physics for studying the properties of matter formed in ultrarelativistic heavy-ion collisions. The main interest is to study the phase diagram and localize phase transitions. In this work we measured the thermodynamic properties of the system produced in such collisions. These parameters were obtained from the transverse momentum distributions of final particles based on several theoretical models. We used well-known hydrodynamic Blast-Wave approach based on Boltzmann statistics. Further, we used a new approach based on q-dual statistics, which can provide more information about the system, in particular its chemical potential and measure the difference of the produced system from the classical equilibrium. We observe that the kinetic freeze-out parameters depend on collision centrality and energy. Results obtained for Blast-Wave model are in agreement with previously published results. For q-dual statistics we can see that in peripheral collisions the system is less equilibrated leading to an increased deviation from the classical distribution.

Abstract

The Spin Physics Detector is an experiment at NICA designed to study the spin structure of the proton and deuteron and the other spin-related phenomena using polarized beams. Two endcap detector wheels of scintillator-based Beam-Beam Counters (BBCs) will be installed symmetrically aside from the interaction point and will serve as a tool for beam diagnostics including local polarimetry. The selection of material combinations for BBC is presented using scintillation tiles with different material combinations of the BBC prototype. The influence of the light collection was studied using matted and covered with Tyvek tiles. Different fibers (Saint-Gobain Crystals BCF91AS, BCF92S, and Kuraray Y-11), as well as different optical cements (CKTN type E, OK-72) were used. The prototypes were tested with cosmic rays and radioactive source using SensL SiPM readout.

This work is devoted to the search for lambda hyperons and short-lived neutral kaons after collisions in the Baryonic Matter at Nuclotron (BM@N) experiment, implemented at the Joint Institute for Nuclear Research (JINR, Dubna). To analyze the effectiveness of strange particle reconstruction algorithms, Monte Carlo simulations of the collision of a 3.9 AGeV Xe beam with a CsI target were used. After reconstruction of events and selection of candidate pairs, distributions of invariant masses were obtained and peaks corresponding to lambda hyperons and neutral kaons were identified. The dependence of the reconstruction efficiency of strange particles on rapidity and transverse momentum was derived.

In this paper, we explore the potential of the colour string model with fusion to describe the azimuthal correlations in proton-proton collisions at (sqrt s = 13) TeV. Our approach is based on a detailed simulation of the longitudinal and transverse dynamics of strings leading to their subsequent fusion and decay. The azimuthal anisotropy appears due to a momentum loss that particles exhibit once they pass through the non-uniform strings’ density. We calculate two-particle correlation function (C(Delta eta ,Delta phi )), corresponding ({{c}_{2}}{ 2} ) cumulant and ({{v}_{2}}{ 2} ) Fourier harmonic by two methods. Results reveal an event multiplicity dependency of these observables, while multi-particle correlations are not induced by the string fusion mechanism.

Recent results on a study of exclusive processes of annihilation into hadrons with the SND detector at the VEPP-2000 collider at center-of-mass energies below 2 GeV are presented. In particular, we discuss new data on the processes ({{e}^{ + }}{{e}^{ - }} to nbar {n}), (pbar {p}), (eta gamma ), (omega {{pi }^{0}}), ({{pi }^{ + }}{{pi }^{ - }}{{pi }^{0}}), and ({{pi }^{ + }}{{pi }^{ - }}{{pi }^{0}}{{pi }^{0}}eta ).