Physics of Particles and Nuclei最新文献

Further development of the approach to the study of relativistic nuclear interactions in the space of four-dimensional velocities using the similarity principle is reported. In essence, the approach is modified by including quark–gluon dynamics in hadron generation during nucleus–nucleus interactions in the central rapidity region. Inclusive spectra of pions and kaons produced in pp and nucleus–nucleus, collisions are studied as a function of their transverse momentum p_T in the central rapidity region calculated within the modified approach based on the assumption of similarity of inclusive hadron spectra. A satisfactory description is given of the NA61/SHINE data for the yield ratios K⁺/π⁺ and K⁻/π⁻ as a function of (sqrt s ) in pp and BeBe collisions. Calculations of antiparticle-to-particle yield ratios (({{bar {p}} mathord{left/ {vphantom {{bar {p}} p}} right. kern-0em} p}), ({{bar {d}} mathord{left/ {vphantom {{bar {d}} d}} right. kern-0em} d}), ({{{{{overline {{text{He}}} }}^{3}}} mathord{left/ {vphantom {{{{{overline {{text{He}}} }}^{3}}} {{text{H}}{{{text{e}}}^{3}}}}} right. kern-0em} {{text{H}}{{{text{e}}}^{3}}}})) in proton–proton and nucleus–nucleus reactions are presented.

The statistics of particles with half-integer spin was constructed in 1926 in the works of E. Fermi and P. A. M. Dirac. Soon after, it was realized that these statistics are extremely important for building a theory of such compact objects as white dwarfs. In this case, there is a limit to the mass of such objects, which is called the Chandrasekhar’s limit. The neutron was discovered by Chadwick in 1932, and already in 1933 Baade and Zwicky suggested that there are neutron stars that arise as a result of supernova explosions and the collapse of a massive core. Pulsars were discovered in 1968 and it was soon realized that pulsars are neutron stars with giant magnetic fields. Binary neutron stars (both in the binary pulsar system and in the kilonova explosion event GW170817) played a key role in the detection of gravitational radiation predicted by general relativity. In 1963, quasars were discovered—fairly compact objects with a gigantic energy release and located at a cosmological distance. It was soon realized that the most natural model of quasars involved a supermassive black hole. Observations of the motions of bright stars in the vicinity of the Galactic center and reconstruction of shadows in the center of the M87 galaxy and the center of our Galaxy based on observations of synchrotron radiation at a wavelength of 1.3 mm provide additional confirmation of the presence of supermassive black holes in the centers of these galaxies.

Abstract

At present, new compact highly granular neutron detector is being developed for the BM@N experiment. This detector will be used to identify neutrons, to measure their energies using time-of-flight method, neutron yields and azimuthal flow of neutrons in heavy-ion collisions at beam energies up to 4 A GeV. Application of machine learning techniques and preliminary results of neutron identification and energy reconstruction are discussed. First predictions of the anisotropic flow of neutrons using the DCM-QGSM-SMM model of heavy-ion collisions are shown.

Abstract

Particles produced in noncentral heavy-ion collisions are mostly twisted (vortex). They are created in electromagnetic and strong interactions. Particles emitted in strong interactions are twisted if initial interacting partons are in twisted states and are untwisted in the opposite case. A vorticity of nuclear matter plays an important role for the production of twisted particles.

Abstract

In this paper we study the cumulative proton production in (p + C) interactions at (4.2) and 10 ({text{GeV/}}c). Cumulative protons in comparison with the noncumulative ones are produced at large values of the variable ({{n}_{{text{c}}}} > 1) and in this region the energy of cumulative protons also increases. The experimentally obtained values of the cumulative proton energies are compared with the estimations got by the formula of the uncertainty principle. It has been shown that the energy of cumulative protons obtained by using the formula of the uncertainty principle is in agreement with the experimental results.

Abstract

Two particles correlations are a useful tool to study the event structures of particle production in multiparticle events of particle interactions. Structures of events are caused by various mechanisms of particle production and could be separated with some global observables of the events. Examining event structures with these methods can give new insight into the nature of these interactions.

The (np to np{{pi }^{ + }}{{pi }^{ - }}) reaction is investigated at the incident neutron momenta ({{P}_{0}}) = 3.83 and 5.20 GeV/c. Contributions of different diagrams to the reaction cross section are calculated at the momenta from the threshold to 12 GeV/c. It is shown that the main contributions to the (np to np{{pi }^{ + }}{{pi }^{ - }}) reaction at momenta above ({{P}_{0}}) > 3 GeV/c come from diagrams of the reggeized (pi )-meson exchange model (OPER).To study spin effects, the reaction (np to np{{Delta }^{{ + + }}}{{Delta }^{ - }}) was separated. It is shown that description of the spin density matrix [({{rho }_{{ij}}})] requires taking into account the ρ-meson exchange diagram. The reaction (np to np{{rho }^{0}}) is separated by background subtraction method. The investigation has shown that ({{rho }^{0}})-meson production is described by suspended diagrams of the OPER model.

Arrays of minibeams of protons and ¹²C in tissue-like media were modeled with Geant4 toolkit. A set of beam energies was used in simulations to provide a Spead-out Bragg peak (SOBP) extended by 6 cm in depth for protons as well as for ¹²C. In both cases, beams of 0.3 or 0.5 mm FWHM were arranged at the entrance to a water phantom either on a rectangular or an hexagonal grid to compare two kinds of projectiles and different minibeam patterns. Differential and cumulative dose-volume histograms (DVH) were calculated and compared for protons and ¹²C as dose uniformity metrics. A uniform dose distribution was easily achieved with protons due to an enhanced lateral scattering of these projectiles in comparison to ¹²C. The cumulative DVHs calculated for 0.3 or 0.5 mm minibeams almost coincide in the target volume, but diverge for different grid patterns. In contrast, cumulative entry DVHs were found similar for both grid patterns, but different for 0.3 and 0.5 mm minibeams.

In this research, we analyze transverse momentum cumulants of different orders (({{K}_{n}})) for charged inclusive hadrons produced in ({text{Bi}} + {text{Bi}}) collisions using the UrQMD-3.4 model events. The analysis is carried out in two ways: with the standard method, in which the study is carried out over the entire rapidity interval, and also with the sub-event method, which suppresses the influence of short-range correlations. Dependencies of second-, third-, and fourth-order cumulants on collision energy were obtained. The paper also provides a comparison of (p + p) and ({text{Bi}} + {text{Bi}}) collisions that indicated the simultaneous saturation for both systems at (sqrt {{{s}_{{NN}}}} approx 5) GeV.

The hadron light-by-light scattering contribution to the superfine splitting of the muonium ground state is calculated. The quasi-potential of muon and electron interaction is expressed in terms of the form factor of transition of two virtual photons to a meson. The contributions of pseudoscalar, pseudovector, scalar, and tensor mesons are considered.