Potential of multiphoton exchange in the scattering of light charged particles of a heavy target

Classical solution of the inverse problem of determing the potential for differential scattering cross section was obtained by O.B. Firsov in 1953. We use it to investigate the deviation from the Coulomb potential due to the exchange of two or more photons in the scattering of an electron in an external field produced by a heavy nucleus with charge Z _e . We also construct the effective potential acting on a charged particle in the problem of planar channeling.     

Antikaon production in nucleon- nucleon reactions near threshold

The antikaon production cross section from nucleon-nucleon reactions near threshold is studied in a meson exchange model. We include both pion and kaon exchange, but neglect the interference between the amplitudes. In case of pion exchange the antikaon production cross section can be expressed in terms of the antikaon production cross section from a pion-nucleon interaction, which we take from the experimental data if available. Otherwise, a K* -resonance exchange model is introduced to relate the different reaction cross sections. In case of kaon exchange the antikaon production cross section is related to the elastic KN and K?N cross sections, which are again taken from experimental measurements. We find that the one-meson exchange model gives a satisfactory fit to the available data for the NN → NN KK? cross section at high energies. We compare our predictions for the cross section near threshold with an earlier empirical parameterization and that from phase space models.     

Double pomeron exchange in the reaction pp → ppπ+π−

We compute the cross section for pp → ppπ⁺π^? in the kinematical region for which two-pomeron exchange is important, assuming dominance of the pion-exchange pole. We include effects due to absorption, final-state interaction, and interference between the two contributing Feynman diagrams. These effects have been ignored in previous calculations. Consequently, our predicted cross section is smaller than previous predictions by a factor of ～ 3, and is consistent with experimental indications. We calculate the background cross section in the double pomeron exchange region, and find that it is sizable even at s ～ 3000 GeV². We discuss the two-particle inclusive process pp → ppX.     

Development of a Method for Measurement of Photonuclear-Reaction Cross Sections with the Aid of Simulated Quasimonoenergetic-Photon Spectra

A procedure for measuring photonuclear-reaction cross sections by employing the method of quasimonochromatization of the bremsstrahlung photon spectrum is developed. This procedure permits determining reaction cross sections via measuring the reaction yield at three fixed values of the electron energy. The procedure is equivalent to measuring the cross section in question for quasimonochromatic photons. Bremsstrahlung-photon spectra are obtained using state-of-the-art simulation means involving the GEANT4 code as applied to a specific experiment with allowance for its geometry, target thicknesses, electron-beam parameters, etc. The results obtained by simulating quasimonochromatic distributions of bremsstrahlung photons are presented for experiments at the LUE-8-5 linear electron accelerator of Institute for Nuclear Research (Moscow, Russian Academy of Sciences). These results are found to be in good agreement with the experimental energy distribution of the cross section for the reaction ¹¹¹Cd(γ, γ') in the energy range between 5 and 8 MeV.     

Minimal total cross section fore + e −→W + W −

The total cross section with the most general form for the gauge boson vertices is given at tree level for the processe ⁺ e ^?→W ⁺ W ^?. Each vertex is parametrized with 7 couplings and the minimum of the total cross section is studied in a wide energy range. Although there are large cancellations between the neutrino exchange diagram and the photon andZ annihilation diagrams, it is surprisingly not possible to get significantly below the standard model cross section for any value of the parameters.     

Kaon production in hadronic matter

Subthreshold kaon production has been studied in symmetric nucleus-nucleus collisions as a function of the nucleus mass, beam energy and centrality. In Au+Au collsions at 1 AGeV theK ⁺ multiplicity increases more than linearly with increasing number of participating nucleons. Transport calculations have to assume a soft equation of state in order to reproduce the data. The in-mediumK ^? cross section measured in Ni+Ni collisions is enhanced by about a factor of 7 as compared to the free cross section when using theK ⁺ cross section at equivalent beam energies as a normalization.     

Ionization,charge exchange,and excitation during collisions of sodium ions with argon

The absolute values of cross sections of ionization, charge exchange, and excitation during Na⁺-Ar collisions are measured in the ion energy range 0.5–10.0 keV. Experiments are performed by a modified method of transverse electric field and by the optical spectrometry method. The mechanisms for realization of inelastic channels are explained qualitatively on the basis of a schematic correlation diagram of diabatic quasi-molecular energy levels of a system of colliding particles. The quasi-molecular nature of interaction is revealed for excitation processes. The excitation mechanisms of collision partners are established. A noticeable contribution to the excitation of the 4s state of the argon atom comes from the cascade transition from upper-lying 4p and 3d levels. An oscillatory structure is observed in the excitation functions of atomic lines of ArI (104.8 and 106.7 nm). The shape of the curve describing the dependence of the charge-exchange cross section on the collision energy is explained by the presence of two nonadiabaticity regions. In the low-energy region (up to E = 2 keV), charge exchange is due to electron capture to the ground state as a result of Σ–Σ transitions, while Σ–Π transitions associated with the rotation of internuclear axis play the leading role in charge exchange in the energy range E > 3 keV. The contribution of a number of inelastic channel is estimated for the ionization process. It is found that the main contribution to ionization is associated with the decay of self-ionization states in an isolated atom.     

Resonant charge exchange in slow collisions involving halogens and oxygen

The coupling of electron momenta is considered for the resonant charge exchange process in slow collisions. Because the electron transfer in this process occurs at large distances between the colliding atomic particles, where ion-atom interactions are relatively weak, we can separate different types of interaction and find the character of coupling of the electron momenta in the quasi-molecule, consisting of the colliding ion and its atom, for real collision pairs. Since the real number of interaction types for colliding particles exceeds that used in the classical Hund coupling scheme, there are intermediate cases of momentum coupling outside the standard Hund scheme. This occurs for the resonant charge exchange involving halogens and oxygen where the quantum numbers of the quasi-molecule in the course of the electron transfer are the total momenta J and j of the colliding ion and atom and the projection M or M_J of the atom orbital or total momentum on the quasi-molecule axis. The ion-atom exchange interaction potential is independent of the ion fine state, and under these conditions, the resonant charge exchange process is not entangled with the rotation of electron momenta, as in case “a” of the Hund coupling. The partial cross section of the resonant charge exchange process depends on quantum numbers of the colliding particles. The average cross sections depend weakly on the coupling scheme.     

Inelastic electron-deuteron scattering with final-state interactions

Measurements of the cross sectiond ² σ/dΩ dE′ for the inelastic electron-deuteron scattering processe+d→e+n+p have been used to determine the electromagnetic structure of the neutron. The effects on the theoretical cross section of the structure of the deuteron and of interactions between the outgoing nucleons are examined in detail. We start with the relativistic invariant expressions of the one-nucleon exchange diagram including deuteron structure to obtain the interaction Hamiltonian. For the disintegration near the quasi-elastic peak thed-n-p vertex function can be represented by nonrelativistic deuteron wave functions. The final state interaction is calculated from phenomenological nucleon-nucleon potentials. The rescattering corrections are found to lead to a decrease in the peak value of the cross section between ?6% and ?2% depending on the electron momentum transfer q² which has been varied between 2.5f ^?2 and 40f ^?2. These corrections are largest for smallq ²<5f ^?2. Furthermore the results show that the influence of our insufficient knowledge of the deuteron structure on the cross section is small.     

The nonlinear effects of quantum electrodynamics at high energies

In this paper we considere ⁺ e ^? scattering with intermediate photon-photon scattering as a possibility for getting information about the nonlinear effects of quantum electrodynamics (QED) at high energies. This process is a higher-order correction to double bremsstrahlung. However, these two processes have quite different behaviour with the photon-photon scattering angle. Here we calculate the unpolarized differential cross section of thee ⁺ e ^? scattering with intermediate γγ scattering and also the interference terms with the double bremsstrahlung. Moreover, we show that the sum of these two contributions predominates over the contribution of the double bremsstrahlung for sufficiently large scattering angles of the photons. This result enables us to extract the differential cross section of the γγ scattering. Through extrapolation to different kinematical conditions we can get the cross sections for nearly real photon-photon scattering, photon splitting and Delbrück scattering. As a quantitative example we use the result for a test of the electron propagator in a gauge-invariant way with the usual minimal interaction. We give also numerical examples of this test, which will improve the present values of the testing parameters.     

γ-γ Physics with peripheral relativistic heavy ion collisions

The high flux of equivalent photons present in relativistic heavy ion collisions of two chargesZ ₁ andZ ₂ gives rise to the collision of two equivalent photons. The cross-sections for various processes are directly related to the correspondingγ- γ cross-sections. As compared toγ- γ physics being studied at e⁺ e^? colliders, we find that high energy states will not be so easily accessible at the existing facilities, however, the enhancement factor (Z ₁ Z ₂)² in the expression for the cross section will provide very large photon fluxes for lower energies.     

The deformation and orientation effect on reaction cross section with deformed targets

The reaction cross section (σ_R) for a deformed target nucleus and spherical projectile is calculated using the optical-limit approximation of the Glauber-Sitenko theory. A method is presented to include both the density-dependent NN interaction and the higher order deformations of the target nucleus in the collision process. We studied both the orientation and the deformation dependence of σ_R within the energy range 30–900 MeV/A. We found that the orientation of the heavy target nucleus (A ≥ 120) can produce a difference in the calculated σ_R up to 30%. The averaged σ_R over all directions of the symmetry axis of the deformed nucleus differs by less than 1% compared with σ_R calculated for a spherical target with the same rms matter radius as the deformed nucleus. For certain orientation, it was found that σ_R is highly dependent on the hexadecapole deformation. The orientation-averaged cross sections show almost no variation with either the sign or the value of the hexadecapole deformation. We compared the average cross section with the experimental data for several mass numbers; fair agreement is obtained.     

Characteristics of double-pomeron exchange

A detailed kinematic study is made of the cross section for double-pomeron exchange. We consider reactions of the type a + b → c + d + (h₁ + h₂ + …) where a → c and b → d are quasi-elastic transitions with limited momentum transfer and (h₁ + h₂ + …) is a centrally produced hadron cluster. The dependence of the cross section on the relative azimuthal angle φ between the final hadrons c and d provides an important test for double-pomeron exchange. We calculate this φ-dependence for all cases of interest, using a model in which pomeron exchange is represented by an effective current-current interaction. For limited momentum transfer, where the pomeron spin is nearly equal to one, this model is equivalent to Reggeized pomeron exchange. We give a complete formalism for the partial-wave analysis of the double-pomeron reaction ab → cd + h₁₂ which differs from the one given by Rushbrooke and Webber. Furthermore, we discuss the two-pomeron vertex, and the construction of detailed and realistic models for double-pomeron reactions.     

Unusual effects of diffraction dissociation for multiproduction in deep inelastic scattering on nuclei

In hadron-nucleus interactions, the stronger is nuclear shadowing in the total cross section the higher is the multiplicity of secondary hadrons. In deep inelastic scattering nuclear shadowing at smallx is associated with the hadronlike behaviour of photons as contrasted to the pointlike behaviour in the non-shadowing region of largex. In this paper we predict dilution of multiproduction of secondary hadrons, and weaker fragmentation of the target nucleus, in deep inelastic leptoptoproduction on nuclei in the shadowing region of smallx as compared to the non-shadowing region of largex. This paradoxial conclusion has its origin in nuclear enhancement of the coherent diffraction dissociation of photons which affects multiproduction in the shadowing region and does not contribute in the non-shadowing region. We present numerical predictions for multiproduction in theμXe interactions studied by the Fermilab E665 collaboration.     

Effect of electric field on photoproduction of electron-positron pairs

The cross section of electron-positron pair production by two circularly polarized photons in a static uniform electric field is calculated. The dependence of the cross section on the photon energy is determined. It is shown that the corrections to the cross section of the process involving photons of various polarizations are suppressed as compared to the situation with crossed fields.     

A dependence of inclusive pion double charge exchange

The A dependence of the forward cross section for inclusive pion double charge exchange on nine target nuclei from ⁶Li to ²⁰⁹Bi at T₀ = 0.59 GeV, as well as the cross section for ⁶Li, ⁷Li, and ¹²C nuclei at T₀ = 0.59, 0.75, and 1.1 GeV, was measured with the 3-m magnetic spectrometer of the Institute of Theoretical and Experimental Physics (ITEP, Moscow). The resulting A dependence is well described within the model involving two sequential single charge exchanges and taking into account the renormalization of the amplitude for pion single charge exchange in a nucleus. A relatively weak energy dependence of the cross section for the ⁶Li, ⁷Li, and ¹²C nuclei agrees with the analogous dependence obtained previously for the ¹⁶O nucleus, but it contradicts the predicted sharp decrease in the cross section within the model involving two sequential single charge exchanges. This result provides an additional piece of evidence that the contribution from the mechanism of inelastic Glauber rescattering is significant at T₀ ? 0.6 GeV.     

A microscopic description of the (γ,pn)-reaction

The quasideuteron process has been investigated for photon energies 40 MeV<E _γ< 160 MeV on the basis of a shell model picture modified by short range nucleon-nucleon correlations. It turns out that the cross section for the (γ,pn)-reaction depends sensitively on the details of the correlation function, i.e. on the exchange of high momenta between otherwise independently moving nucleons. The final state interaction has been consistently taken care of by using optical model wave functions for the outgoing nucleons. The results of the calculations for¹⁶O indicate that precise measurements of the (γ,pn) cross section do contain information on the properties of the nuclear wave functions for small internucleonic distances.     

Estimation of cross section of a Δ resonance in <Emphasis Type="Italic">pA</Emphasis> collisions for internal target of nuclotron

The two-stage process of a Δ-resonance production in a target nucleus is considered. The analysis of the reaction uses a kinematic calculation of a cross section in pion production in pA inelastic collisions, and the subsequent interaction of produced pions with the target nucleus is analyzed. In particular, a simple technique to estimate the cross section of Δ-resonance production is offered for the carbon target. This technique allows one to estimate the total cross section of Δ-resonance production at rest, depending on the energy value of incident particles. Calculations of the efficiency of a resonance registration for the internal target of the Nuclotron at the SCAN setup are presented.     

Manifestations of a dineutron cluster in elastic α 6He scattering

A consistent theoretical analysis of elastic α ⁶He scattering is performed with allowance for the correction associated with the exchange of a dineutron cluster. It is shown that the inclusion of the exchange mechanism, along with that of potential scattering, makes it possible to reproduce the measured cross section over the entire range of the ⁶He scattering angle. Concurrently, one can also obtain information about the spatial distribution of the dineutron cluster and the α particle in the ground state of the ⁶He nucleus.