Vol 86, No 1 (2023)

The explosion of a minimal-mass neutron star formed in the course of the evolution of a close binary of neutron stars markedly differing in mass is considered. The abundance of heavy elements produced during the expansion of matter of the external neutron-star core after the explosion of a low-mass neutron star is calculated. It is shown that, in this scenario, a weak r-process proceeds in the external core, leading to the formation of a ‘‘light’’ fraction of heavy elements.

New antineutrino spectra of fissile isotopes entering into the composition of nuclear-reactor fuel are obtained. A method that combines a calculation of antineutrino spectra and a fit of the results to the spectra obtained experimentally at the Rovno nuclear power plant in the 1980s is used. The cross sections calculated for fissile isotopes by employing these spectra describe well the cross section of 
 cm
fission obtained in the Double Chooz experiment. The cross section obtained on the basis of the calculated spectra at the same composition of the reactor core is 
 cm
fission. For the resulting spectra, there is no problem of a bump in the region around 5 MeV in the observed energy spectrum of positrons.

One-loop electroweak radiative corrections to dilepton production in the channel of photon fusion in hadron–hadron collisions are estimated for the LHC (Large Hadron Collider) experimental program aimed at studying the Drell–Yan process. A detailed numerical analysis of effects associated with electroweak radiative corrections to observables (cross sections and the forward–backward asymmetry) is performed over a wide kinematical region, including that of the CMS experiment at the LHC in the Run3/HL mode, which corresponds to ultrahigh energies and dilepton invariant masses.

The role of closed and deformed proton and neutron shells in the fission of 
Cf and 
Fm nuclei at excitation energies from 40 to 56 MeV is studied. The mass–energy distributions of fission fragments of these nuclei formed in the 
Th and 
U reactions at projectile-ion energies close to the Coulomb barrier are measured by means of the CORSET time-of-flight spectrometer. It is shown that, in all of the reactions under study, an enhanced yield of fragments in the mass region around 100 a.m.u. is due to the effect of the 
 deformed proton shell. A manifestation of a supershort mode is found in the fission of 
Fm at the compound-nucleus excitation energy of 40 MeV.

A theoretical analysis of available experimental data on elastic and inelastic 
C scattering in the energy region extending up to 90 MeV is performed. The parameters of a semimicroscopic potential are found on the basis of the dispersive optical model. The potentials found in this way are used in analyzing, by the distorted-wave Born approximation, data that the authors recently measured for inelastic scattering at energies of 65 and 90 MeV. Experimental data for the states at 3.68 and 7.55 MeV are presented for the first time. These states are considered under the assumption that, within the standard rotational model, they are members of the ground-state rotational band. A satisfactory description of angular distributions is obtained, and deformation lengths are determined. A model phenomenological form factor is used for the remaining excitations in the energy range extending up to 11 MeV. The present analysis confirms the presence of a neutron halo in the 3.09-MeV state. A similarity of form of the inelastic form factors obtained for the 8.86-, 10.996-, and 11.08 MeV states and the proximity of their radii gives grounds to assume that the 
C nucleus in these three states has an enhanced size and similar structures. A comparison of the radial dependences of the form factors for the 9.90- and 8.86-MeV states shows that the wave function for the 9.90-MeV state has a substantially smaller spatial extension. These results agree with the values obtained for the radii of the states under discussion on the basis of the modified diffraction model.

A natural mixture of molybdenum isotopes was irradiated with bremsstrahlung having the endpoint energies of 20 and 55 MeV. The irradiated targets were studied by means of spectrometers featuring detectors from ultrapure germanium. The spectrum-weighted average yields of the (
) reactions were determined. The values obtained in this way were compared with the results of calculations based on the statistical model of the nucleus. The partial contribution of semidirect processes to the yields of the reactions being studied was estimated.

The results obtained for the energies of bound states of the 
Li nucleus and for the respective asymptotic normalization coefficients, as well as for the energies and widths of its resonance states, by the SS-HORSE method on the basis of ab initio calculations within no-core shell model with Daejeon16 nucleon–nucleon interaction are presented.

The structure of the wave functions for the 
O(g. s.; 3@) nucleus is studied by employing experimental angular distributions of the differential cros@ sections for the reactions 
O@O(g. s.; 3@) and @N@O(g. s.; 3@) at 
 MeV. The present analysis is carried out by the coupled-channel method with allowance for direct mechanisms (proton stripping and transfer of a 
C heavy cluster) and on the basis of the compound-nucleus model. Each of the mechanisms under consideration is associated with a specific configuration of the wave function for the @O nucleus and is found to make a significant contribution to the experimental cross section.

In a special laboratory frame, the differential cross sections 
 for the fission of nonoriented target nuclei that is induced by cold polarized neutrons 
 and which is accompanied by the emission of light particles 
, such as prescission alpha particles or prompt neutrons 
, and photons can be represented as the sum of two terms. The first term is equal to the cross section for the analogous reaction induced by unpolarized neutrons, 
, where 
 is the total cross section for this reaction and 
 is the angular distribution of light particles 
 emitted in this reaction. The second term in this sum, 
, depends linearly on the neutron polarization vector 
 and describes 
-even 
-odd asymmetries in the original cross section. By employing the concepts of space isotropy and parity conservation, it is possible to represent the cross section 
 as the sum of two scalar functions, 
, which are related to the correlation functions (
) and (
)(
) that are, correspondingly, even and odd under the transformation 
, where 
 and 
 are the wave vectors of the light fission fragment and the light particle, respectively. These correlation functions can be expressed in terms of the quantities 
, whose experimental values can be found from the experimental values of the asymmetry coefficient 
 introduced earlier [1] and the angular distribution 
 of light particles by employing the relation 
. Within the quantum-mechanical approach, the theoretical values of 
 can be obtained by means of the formula 
, which takes into account the angle 
 of rotation of the light-particle wave vector 
 about the wave vector 
 of the light fission fragment under the effect of Coriolis interaction associated with the collective rotation of the fissioning system about the axis orthogonal to its symmetry axis. The angle of rotation is determined from a comparison of the experimental and theoretical values of 
 with the aid of the maximum-likelihood method. Because of taking into account quantum interference effects, 
 may in general take not only positive (as is the case within the semiclassical method of trajectory calculations [1]) but also negative values. The use of this result permits reaching reasonable agreement between the experimental and theoretical values of 
 for all 
 particles simultaneously in the cases of 
U, 
Pu, and 
Pu target nuclei. In the case of the 
U target nucleus, however, the quantity
, which is independent of the angle 
, should be supplemented with 
 in order to reach the same degree of agreement. The appearance of the latter may in principle be due [1] to the violation of axial symmetry of the fissioning system because of the effect of its bending and wriggling vibrations in the vicinity of the scission point.

A comparative analysis of experiments devoted to studying, in the fission process, (
) angular correlations, on one hand, and (
) and (
) angular correlations, on the other hand, is performed on the basis of the model proposed earlier for describing muon conversion in fragments originating from the prompt fission of 
U nuclei that is induced by negatively charged muons. It is shown that each of these experiments may provide information that does not depend on the results of the other experiments and which is complementary to them. Historically, the situation resembles the Einstein–Podolsky–Rosen (EPR) paradox. An experimental verification of the theoretical relation between the alignment and polarization of fragment spins in the CORA experiment is of crucial importance.

The energy spectra of neutrinos of type II supernovae under various explosion mechanisms are considered. For dynamo active supernovae it is shown that effective neutrino collisions in magnetized nucleon gas caused by the Gamow–Teller component of the neutral current lead to neutrino acceleration. Such an increase in the hardness of the neutrino energy spectrum is favorable for observations of supernova neutrinos using neutrino telescopes. The possibilities of detecting neutrinos of supernovae by large-volume observatories (KM3NeT and Baikal-GVD) are discussed.

Precise measurement of beta spectra was always of great importance in some fundamental problems, including those of neutrino physics. The results obtained by measuring the spectrum of a Ce–Pr source with setups of two types to a precision substantially improved in relation to earlier investigations are presented. The correctness of a theoretical fit is tested using the shape of the Pr (0)Nd (1) allowed beta transition.

Ultraperipheral collisions belong to special type of heavy-ion collisions since strong interactions are suppressed in them because of large impact parameters of such collisions. Such conditions provide a unique possibility for studying two-photon interactions. In particular, interest in studying the production of tau-lepton pairs and Light-by-Light (LbyL) scattering has grown in recent years: a deviation of the cross sections for these processes from the predictions of the Standard model could be a manifestation of new physics. In addition, the search for the production of axion-like particles in LbyL scattering at rather low invariant masses is of interest in and of itself. The most recent results of experiments performed at the Large Hadron Collider and devoted to measurement of the tau-lepton anomalous magnetic moment and cross sections for LbyL scattering and to the search for axion-like particles are discussed in the present article, along with prospects of future measurements in the ALICE experiment.

Elliptic flow is among basic observables that characterize collective effects at the initial stage of formation of quark–gluon plasma in collisions of ultrarelativistic nuclei. The yields of neutral pions are measurable up to high transverse-momentum values; therefore, measurement of the elliptic flow for neutral pions is an efficient means for studying quark–gluon plasma. Measurement of the elliptic flow in asymmetric collision systems makes it possible to study the dependence of the elliptic flow on the initial geometry of the system. Two procedures for measuring the elliptic flow for neutral pions in the  asymmetric collision system at the energy of  GeV are considered.

The possibility of measuring antiproton production in heavy-ion collisions at the NICA (Nuclotron based Ion Collider fAcility) accelerator complex in a kinematical region that is forbidden for nucleon–nucleon interaction is considered. It is shown that, at pseudorapidities accessible to measurements with the aid of the NICA detectors and which lie in the range of 
–1.5, the transverse momentum of an antiproton produced on a cluster formed by two nucleons does not exceed 6 GeV and is nearly twice as great as the transverse momentum of an antiproton produced in nucleon–nucleon interaction.

The results of a comparative analysis of mean values of various kinematical characteristics of protons in C and C collisions at 4.2 GeV/ are presented. The mean values of the total proton momentum are found to be different in these collisions. It is shown that the inclusive rapidity spectra of protons agree in the target fragmentation region.

Parameters of the model involving three active and three sterile neutrinos are estimated. Specifically, these are the parameters of mixing of active and sterile neutrinos and mass parameters of sterile neutrinos. In doing this, use is made of the results of the BEST (Baksan Experiment on Sterile Transitions) experiment. The BEST experiment is aimed at testing the gallium anomaly at short distance—that is, the deficit of electron neutrinos from a radioactive source. In addition, the results of experiments devoted to testing the accelerator and reactor anomalies at short distances are taken into account along with some astrophysical data.

Proposals of possible experiments based on employing a spin-physics detector (SPD) at the first stage of implementation of the NICA (Nuclotron based Ion Collider fAcility) research program are considered. The proposals include studies of collisions of polarized and unpolarized proton and deuteron beams at effective nucleon–nucleon energies of 
 GeV in the center-of-mass frame.

With the aim of developing the hydrodynamic approach to describing collisions of intermediate-energy heavy ions, it is proposed to solve simultaneously the equations of hydrodynamics and the kinetic equation. This makes it possible to include the nonequilibrium component in the present analysis and to describe successfully experimental data obtained at Institute for Theoretical and Experimental Physics (ITEP, Moscow) for the double-differential cross sections of the emission of cumulative protons, pions, and photons in collisions carbon nuclei with a beryllium target in the energy range between 2.0 and 3.2 GeV per nucleon. The correction for the microcanonical distribution and the contribution of the fragmentation process to the proton yield are taken into account in describing these spectra. The resulting description of these experimental data turns out to be better than the descriptions based on cascade models and models of quantum molecular dynamics. A comparison with other reactions and approaches is performed. It turns out that effects of short-range correlations are included in the proposed approach, since it provides a successful description of experimental hard-photon spectra, which are described within molecular dynamics only upon adding a high-momentum component.