Physics of Atomic Nuclei最新文献

The paper presents an original solution to the muography study of the ancient Spaso-Kamenny Preobrazhensky Monastery territory on Kamenny Island in Lake Kubensky (Vologda Region, Russia). Two points highlight the approach’s originality: validating the reliability of data analysis algorithms by recognizing visually verifiable structures and a thorough examination of experimental data from near-horizon atmospheric muon fluxes. The research enabled the identification of underground density anomalies within the Monastery grounds.

The deuteron–proton elastic scattering process is considered in the relativistic expansion framework. Four reaction mechanisms are taken into account: plane-wave impulse approximation, single-scattering, double-scattering terms, and delta-isobar in the intermediate state. Each of these terms contributes into the reaction amplitude. The method allows calculating both the differential cross section and any polarization observables. The calculations are performed in a GeV-energy range for the special case when the scattering angle is equal to 180 degrees. The results are given for various deuteron wave functions: Paris, CD Bonn, and Gross.

The problem of taking into account radial and tangential friction in the entrance channel of ({}^{36}textrm{S}+{}^{238})U and ({}^{64}textrm{Ni}+{}^{238})U nuclear reactions occurring at a nonzero impact parameter is considered. The reactions in question are simulated in the approximation of frozen deformation degrees of freedom of colliding nuclei. The shape of the target nucleus is elongated, and its symmetry axis is oriented arbitrarily in the plane drawn through the initial projectile momentum and the center of mass of the target nucleus. The shape of the projectile nucleus remains spherical throughout the process of collision of primary nuclei. The dynamical evolution of two degrees of freedom of the system is considered; these are a parameter that describes the distance between the centers of mass of colliding nuclei and a parameter that describes the orientation of the target nucleus. It is shown that the inclusion of tangential friction between colliding nuclei makes it possible to avoid overestimating the probability for projectile capture by the target nucleus at high angular momenta. The results of the simulation are compared with experimental data and with the results of calculations based on the earlier version of the model.

One of the most effective ways to investigate quark–gluon plasma (QGP) properties is to measure the azimuthal particle anisotropy in momentum space. This anisotropy can be characterized by the elliptic flow ((v_{2})). The evolution of the elliptic flow can be studied by using these two approaches: either measure (v_{2}) values in different collision systems or use different particles of interest. Varying collision systems allows to investigate the impact of initial conditions on (v_{2}) values. Also, using small-system collisions provides the opportunity to measure (v_{2}) values in low multiplicity regions, where the conditions for QGP formation may be unachievable. Neutral pion is considered a unique tool to study (v_{2}) development mechanisms, because its yields are measurable up to large transverse momenta ((p_{T})) in small and large collision systems, where different effects of (v_{2}) development can dominate. This work is dedicated to the measurement of the (v_{2}) values for (pi^{0}) mesons as a function of (p_{T}) and centrality in small collision system—({}^{3})He (+) Au, and the largest collision system at RHIC—U (+) U.

Mueller–Navelet dijet production is studied within the framework of the High–Energy Factorization formalism as it is formulated in the Parton Reggeization Approach. Parton amplitudes with Reggeized gluons calculated within the L.N. Lipatov’s Effective Field Theory which ensures their gauge invariance. We performed our calculations using two different resummation schemes: modified Kimber–Martin–Ryskin–Watt and Blumlein. Since this process is considered as a direct probe of small–(x) physics, we especially study contributions with the BFKL resummation. The results of calculations are compared with the CMS Collaboration data.

In this paper, recent results on the production of protons, deuterons and tritons from the BM@N experiment at NICA are presented. We discuss transverse momentum spectra and rapidity distributions of (p), (d), (t) from centrality selected Ar (+) nucleus collisions at the beam kinetic energy of 3.2 GeV per nucleon. The rapidity and mass dependence of the particle average transverse momentum is presented in different collision systems. The deuteron-to-proton ratio in rapidity bins is obtained in centrality selected collisions.

New data for cross sections of partial reactions ((gamma,1n)) and ((gamma,2n)) were obtained using both published data for neutron yield cross section (sigma(gamma,xn)=sigma(gamma,1n)+2sigma(gamma,2n)) and total photoneutron reaction cross section (sigma(gamma,sn)=sigma(gamma,1n)) + (sigma(gamma,2n)) determined in experiment on the bremsstrahlung beam. The investigation of reliability of those cross sections was carried out using the experimental-theoretical method for partial reaction cross section evaluation based on physical criteria. It was found that new evaluated cross sections of the reactions ({}^{115})In((gamma,1n))({}^{114})In and ({}^{115})In((gamma,2n))({}^{113})In meeting physical criteria of reliability differ in a certain way from experimental ones. The comparison of new evaluated data with the results of analogous evaluation based on the results for partial reaction cross sections for ({}^{115})In obtained in experiment on the beam of quasi-monoenergetic annihilation photons shows that both evaluations are close.

The Minkowski vacuum is perceived by an accelerated observer as a medium with a finite temperature, which is the essence of the well-known Unruh effect. It turns out that in addition to temperature, a finite shear viscosity appears in the accelerated system, and this viscosity satisfies the lower limit from string theory (eta/s=1/4pi). We describe the derivation of the corresponding shear viscosity for electromagnetic field.

A special class of solutions of the equations of cosmological dynamics implying analytic connection between inflationary models in the framework of general relativity and Einstein–Gauss–Bonnet gravity is considered. The possibility of verification of such models by direct observation of relic gravitational waves, the spectrum of which is determined by the parameters of the model was analyzed.

The observation of gravitational waves from cosmological distances is one of the future tools for testing the hypothesis of the existence of primordial black holes (PBHs). Their clustering plays a decisive role in predicting their mergers. We show that in this case the merger rate differs from the predictions of the model without initial clustering. Also, our results on the merger rate are sensitive to the parameters of the PBH cluster formation models. Future observations of black hole mergers at high redshifts will be able to test the possibility of PBH clustering.