Vol 82, No 2 (2019)

It is shown that, upon the stopping of a negatively charged kaon and its absorption by a nucleus, there arise particles whose appearance does not comply with thermodynamic evaporation theory. An identification of these particles by various methods makes it possible to evaluate the nearly identical yields of ³H and ³He nuclei. This result may serve as an indication that direct reactions induced by interaction with ⁴He are observed in K⁻-meson absorption in nuclei.

The possibility of experimentally determining the ratio λ of the axial weak-interaction constant G_A to the vector weak-interaction constant G_V by simultaneously measuring the electron and neutrino asymmetries at the same setup is discussed. The proposed measurement and data-processing procedures are described in detail. The determination of λ by the method in question permits disregarding the possible contribution of the Fierz interference term and dispensing with an accurate measurement of the neutron polarization. It is shown that this method makes it possible to measure λ to a precision at a level of 10⁻⁴.

The energy as determined experimentally for the first excited 2⁺ state of the ¹⁵⁶Gd rotational band based on the mixed-symmetry state is extremely small in relation to characteristic values of this energy in deformed nuclei. The possibility of explaining this experimental fact by a large value of the decoupling parameter is explored. The result is that the decoupling-parameter values obtained under various assumptions on the structure of the mixed-symmetry state are too small for explaining the experimental excitation energy of the state in question.

In order to explain elastic neutral-pion photoproduction on a ⁷Li nucleus in the excitation-energy region of the Δ(1232)3/2⁺ resonance, a new interpretation of coherent pion photoproduction on nuclei featuring two or more shells is proposed with allowance for a special feature of inelastic pion photoproduction on a nucleon. Coherence originating from nucleons of different nuclear shells is retained, while coherence from all of the nucleons is removed, since, after pion production on nucleons from different shells, they cannot cannot be in the same phases because of the difference in the conditions of their residence in the nucleus. Under this assumption, a noncontradictory description of all experimental data is obtained upon additionally including the interaction of Δ isobars in the nucleus that are produced along with neutral pions.

The results obtained from a phenomenological analysis of the ratio of the elastic-to-total cross sections for proton-proton (pp) and antiproton-proton (\((\bar pp)\)) scattering as a function of energy are presented. Analytic functions proposed on the basis of studying low- and high-energy experimental data for various scattering parameters make it possible to obtain a statistically acceptable quantitative description of the energy dependence of this ratio over a broad energy region of \(\sqrt s \ge 3\) GeV for individual samples of pp and \(\bar pp\) collisions and over the region of \(\sqrt s \ge 5\) GeV for a combined ensemble of experimental data. On the basis of the resulting approximations, the ratio of the elastic-to-total cross sections for pp collisions are estimated at various values of \(\sqrt s \) up to an ultrahigh energy of \(\sqrt s = 10\) PeV. The resulting estimates may prove to be useful for experiments at currently operating and future hadron colliders, as well as for measurements of ultrahigh-energy cosmic rays. An indication of the onset of the asymptotic region for the cross-section ratio in question is observed in the region of \(\sqrt s \mathbin{\lower.3ex\hbox{$\buildrel>\over {\smash{\scriptstyle\sim}\vphantom{_x}}$}} 5 - 10\) PeV.

The effects of vacuum polarization for a massless scalar field φ(x) in the vicinity of a pointlike source that has a zero-range potential are analyzed in four-dimensional Minkowski space. An exact expression for the regularized scalar-field Hadamard function is obtained by means of the technique of self-adjoint extensions, and the renormalized vacuum expectation values of the scalar field squared, ⟨φ² (x)⟩_ren, and of the operator of the scalar-field energy—momentum tensor, ⟨T_μν(x)⟩_ren, are calculated.

Experimental data on πN scattering in the elastic energy region w ≤ 1.45 GeV are analyzed within the K-matrix approach with effective lagrangians. The charge splitting in δ₃₃⁺⁺ and δ₃₃⁰ phases obtained in the phase-shift analisys is studed. It is shown that the change in the sign in the energy dependence of the phase difference can be obtained with different form factors of the Δ⁺⁺ and Δ⁰ only. This means that πNΔ⁺⁺ and πNΔ⁰ interactions have a different range. The underlying nature of the observed phenomena is discussed.

In the soft-photon approximation, compact expressions for two-loop final-state electromagnetic radiative corrections to the four-fermion process in the s channel are obtained on the basis of the on-shell renormalization scheme. As applied to the Drell—Yan process, an efficient procedure for numerically estimating final-state radiative effects is proposed for experiments at the LHC for high invariant masses.