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Register a new userCoulomb-nuclear interference in pion-nucleus bremsstrahlung
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Pion-nucleus bremsstrahlung offers a possibility of measuring the structure functions of pion-Compton scattering from a study of the small-momentum-transfer region where the bremsstrahlung reaction is dominated by the single-photon-exchange mechanism. The corresponding cross-section distribution is characterized by a sharp peak at small momentum transfers. But there is also a hadronic contribution which is smooth and constitutes an undesired background. In this communication the modification of the single-photon exchange amplitude by multiple-Coulomb scattering is investigated as well as the Coulomb-nuclear interference term.
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At low photon energies, the potential models of nucleus-nucleus bremsstrahlung are based on electric transition multipole operators, which are derived either only from the nuclear current or only from the charge density by making the long-wavelength approximation and using the Siegert theorem. In the latter case, the bremsstrahlung matrix elements are divergent and some regularization techniques are used to obtain finite values for the bremsstrahlung cross sections. From an extension of the Siegert theorem, which is not based on the long-wavelength approximation, a new potential model of nucleus-nucleus bremsstrahlung is developed. Only convergent integrals are included in this approach. Formal links between bremsstrahlung cross sections obtained in these different models are made. Furthermore, three different ways to calculate the regularized matrix elements are discussed and criticized. Some prescriptions for a proper implementation of the regularization are deduced. A numerical comparison between the different models is done by applying them to the $alpha+alpha$ bremsstrahlung.
A dynamical model based on effective Lagrangians is proposed to describe the bremsstrahlung reaction $ pi N to pi N gamma$ at low energies. The $Delta(1232)$ degrees of freedom are incorporated in a way consistent with both, electromagnetic gauge invariance and invariance under contact transformations. The model also includes the initial and final state rescattering of hadrons via a T-matrix with off-shell effects. The $pi N gamma$ differential cross sections are calculated using three different T-matrix models and the results are compared with the soft photon approximation, and with experimental data. The aim of this analysis is to test the off-shell behavior of the different T-matrices under consideration.
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Sergei P. Maydanyuk Instituten for Nuclear Research
, National Academy of Sciences of Ukraine
2019
Bremsstrahlung emission of photons during nuclear reactions inside dense stellar medium is investigated in the paper. For that, a new model of nucleus is developed, where nuclear forces combine nucleons as bound system in dependence on deep location inside compact star. A polytropic model of stars at index $n=3$ with densities characterized from white dwarf to neutron star is used. Bremsstrahlung formalism and calculations are well tested on existed experimental information for scattering of protons of light nuclei in Earth. We find the following. (1) In neutron stars a phenomenon of dissociation of nucleus is observed --- its disintegration on individual nucleons, starting from some critical distance between this nucleus and center of star with high density. We do not observe such a phenomenon in white dwarfs. (2) In the white dwarfs, influence of stellar medium imperceptibly affects on bremsstrahlung photons. Also, we have accurate description of bremsstrahlung photons in nuclear reactions in Sun. (3) For neutron stars, influence of stellar medium is essentially more intensive and it crucially changes the bremsstrahlung spectrum. The most intensive emission is from bowel of the star, while the weakest emission is from periphery.
We investigate an idea, how to use analysis of the bremsstrahlung photons to study the internal structure of proton under nuclear reaction with nucleus. A new model is constructed to describe bremsstrahlung emission of photons which accompanies the scattering of protons off nuclei. Our bremsstrahlung formalism uses many-nucleon basis that allows to analyze coherent and incoherent bremsstrahlung emissions. As scattered proton can be under the influence of strong forces and produces the largest bremsstrahlung contribution to full spectrum, we focus on accurate determination of its quantum evolution concerning nucleus basing on quantum mechanics and scattering theory. For such a motivation, we at first time generalize Pauli equation with interacting potential describing evolution of fermion inside strong field, with including the electromagnetic form-factors of nucleon basing on DIS theory. Anomalous magnetic momenta of nucleons reinforce our motivation to develop such a formalism, starting from low energy. The full bremsstrahlung spectrum in our model (after renormalization) is dependent on form-factors of the scattered proton. For calculations, we choose the scattering of $p + ^{197}{rm Au}$ at proton beam energy of 190~MeV, where experimental bremsstrahlung data were obtained with high accuracy. We show that the full bremsstrahlung spectrum is sensitive to the form-factors of the scattered proton. In the limit without such form-factors, we reconstruct our previous result (where internal structure of the scattered proton was not studied).
Using a simple final-state rescattering model coupled with a simple Coulomb model, the effects of the central Coulomb potential on pion interferometry measurements in 158 GeV/nucleon Pb+Pb collisions are explored. Although the central Coulomb potential does not introduce correlations between pions, it does prevent an accurate measurement of the momentum difference. This momentum difference smearing effect leads to a reduction in the measured correlation radii and lambda parameters. These distortions are important in 158 GeV/nucleon Pb+Pb collisions because of large source sizes and the strong central Coulomb potential.
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