O.D. Dalkarov

The origin of P-wave enhancement in the optical model for low-energy proton-antiproton scattering

The observed large P-wave contribution to the NN interaction at low energies, reproduced by the optical-model calculations, is shown to be caused by the S-matrix poles which correspond to the P-wave states located close to the NN threshold.

Scattering of low-energy antiprotons from nuclei

Abstract It is shown that the mechanism of low-energy antiproton scattering from nuclei is given by the Glauber model including Coulomb effects. The cross sections for elastic and inelastic (with excitation of nuclear level) p scattering from 12C and 16O and also for elastic scattering from 40Ca and 208Pb are calculated without any free parameters. Calculations are in good agreement with LEAR data. The real-to-imaginary ratios of the p N scattering amplitude are found from antiprotonnucleus cross sections at diffractive minima at energies of 46.8 and 179.7 MeV, which also agree with LEAR values of this ratio. The antiproton-nucleus optical potential and scattering lengths are calculated. Shifts of the 3d levels of the antiproton atoms p 12 C and p 16 O are estimated and are found to be in good agreement with experiment.

Elastic and inelastic scattering of low energy antiprotons from 12C and 16O nuclei

Abstract The differential cross sections for elastic scattering and cross sections for excitation of the nuclear level by low energy antiprotons from carbon and oxygen nuclei are calculated without any free parameters. The theoretical curves agree with experimental data at 46.8 Me V which have been obtained at LEAR. We predict the differential cross sections for the excitation of the nuclear level with definite spin projection of excited nucleus. They determine angular γ-quanta distributions in ( p , p γ) reactions on nuclei.

On the electromagnetic form factors of hadrons in the time-like region near threshold

Abstract Hadron electromagnetic form factor in the time-like region at the boundary of the physical region is considered. The energy behavior of the form factor is shown to be determined by the strong hadron–antihadron interaction. We propose a simple phenomenological model of the h h ¯ interaction that describes the form factor behaviour in the region where scattering length approximation fails and estimate on its basis imaginary part of the scattering lengths (volumes) for Λ Λ ¯ , Λ Σ ¯ 0 ( Λ ¯ Σ 0 ) , Σ 0 Σ ¯ 0 and D ∗ D ∗ ¯ from present experimental data. The developed approach enables us to analyze the existence of baryon–antibaryon ( B B ¯ ) near threshold resonances. The experiments to extract detailed information on the near threshold B B ¯ interaction from hadron form factor energy behavior are suggested.

e+e− annihilation near N̄N threshold

Abstract The contribution of nucleon-antinucleon states (real and virtual) to electron-positron annihilation near the NN threshold is investigated theoretically. The nucleon electromagnetic form factor in the time-like region is calculated within the coupled-channels model. Its behaviour is shown to be predominantly denned by the nuclear NN interaction in the initial state. The neutron form factor does not exceed the proton one. New experimental data, revealing the existence of minima in many-pionic e + e - annihilation cross section near the NN threshold, are described. An analysis of the observed irregularity shows an existence of the narrow state in the NN system with the mass approximately 1800 MeV and the width about 15 MeV.

Proton electromagnetic form factor in the time-like region

Abstract The proton electromagnetic form factor in the time-like region at the boundary of the physical region is considered. The energy behaviour of the form factor is shown to be dominantly determined by the strong nucleon-antinucleon interaction. This allows to determine the pp triplet scattering length from the experiments on the proton form factor.

On a possible nearthreshold ΛΛ state

The behaviour of the pp→ΛΛ reaction cross section near the ΛΛ threshold is described within a hermitian coupled-channels approach. The observed structure is shown to be caused by a narrow ΛΛ subthreshold state of quasinuclear nature. This resonance with quantum numbers JPC=1−− is produced in the 3SD1 partial wave and has a width of a few MeV. The physical reasons for the smallness of its width are explained. Other experimental possibilities to find this resonance are proposed.

Nonadiabatic effects in nuclear reactions and the problem of determination of the proton electromagnetic form factor in the nonphysical region

Abstract It is shown that in nuclear reactions a considerable cancellation takes place between some nonadiabatic effects associated with the nonstatic nature of nucleons, coupled with the fact that they are bound and with off-shell properties of the elementary amplitudes. A technique is developed which allows us to study the above effects at low, medium and high energies in both elastic and inelastic scattering. Parameters which characterize the cancellation of nonadiabatic effects are: obtained. It is shown that a certain choice of the energy variable in the elementary amplitude is advantageous in describing quasielastic reactions. This choice corresponds to the collision of an incident particle with a free nucleon whose momentum equals the Fermi momentum of the nucleon being knocked out. The results are applied to study the possibility of extracting the proton electromagnetic form factor in the nonphysical region from the pd → e + e − n s data. It is found that due to the cancellation the amplitude of the virtual annihilation effectively enters the pole diagram at q 2 ⩾ 4 m 2 independently of the kinematical range of the external variables. The near-threshold behaviour of the amplitude obtained when extracting it from the pd — e + e − n s data by means of the commonly used “quasifree” approximation (pole graph) is predicted.

Low-energy antiprotons as a new probe of nuclear reaction mechanism

Abstract The experimental data of LEAR, KEK and BNL on low-energy antiproton interaction with nuclei are analysed in the framework of the Glauber-Sitenko approach. It is shown that antiproton-nucleus interaction gives new information on the nuclear reaction mechanism, on nuclear structure and on parameters of the p N amplitude.

A spectroscopy approach to measure the gravitational mass of antihydrogen

We study a method to induce resonant transitions between antihydrogen