Physics of Atomic Nuclei最新文献

To search for proton Electric Dipole Moments (EDM) using proton storage ring with purely electrostatic elements, the concept of frozen spin method has been proposed by Brookhaven National Laboratory. This method is based on two facts: in the equation of spin precession, the magnetic field dependence is entirely eliminated, and at the ‘‘magic’’ energy, the spin precession frequency coincides with the precession frequency of the particle momentum. In case of deuteron, we have to use the electrical and magnetic field simultaneously, keeping the frozen spin direction along the momentum as in the pure electrostatic ring. Later, Yu. Senichev proposed the concept of quasi-frozen spin, in which the spin oscillates around the direction of the pulse within half the value of the advanced phase of rotation in magnetic arcs, each time returning back in deflectors with an electrostatic field. Due to the low value of the anomalous magnetic moment of deuteron, an effective contribution to the expected EDM effect is reduced only by a few percent compared with frozen spin method. In this work, we consider the adapted structure of the NICA and Nuclotron synchrotrons, in which the ‘‘quasi-frozen spin’’ option can be implemented. The advantage of the ‘‘quasi-frozen spin’’ concept is the possibility of using synchrotrons already existing in the world that are not focused on studying EDM, which makes this method the only one possible for the accelerators of the NICA complex.

We present a new relativistic expression for the Sommerfeld–Gamow–Sakharov factor ((S)-factor) of a composite system of two spin-1/2 particles of arbitrary masses interacting via a via aCoulomb-like chromodynamical potential. The analysis is performed in the framework of a relativistic quasipotential approach based on the Hamiltonian formulation of the covariant quantum field theory in the relativistic configuration representation suggested by A.A. Logunov, A.N. Tavkhelidze and V.G. Kadyshevsky. The pseudoscalar, vector and pseudovector systems are considered and the behavior of the (S)-factor near the threshold and in the relativistic limit is investigated in detail. It is argued that at the threshold the contribution of spins significantly reduces the Sommerfeld effect, while at ultrarelativistic velocities their role diminishes and the (S)-factor becomes basically the same as for the spinless systems.

The strength distributions of charge exchange spin-dipole excitations are calculated in the continuum quasiparticle random-phase approximation based on the Fayans density functional with modified isovector part. An impact of the isovector parameter (h_{2}^{-}) of the DF3-f functional on the strength functions of charge-exchange spin-dipole excitations ((0^{-}), (1^{-}), (2^{-})) are studied for ({}^{208})Pb, ({}^{132})Sn and ({}^{90})Zr. The sum rules are calculated using both ground state radii and direct integration of the total SD strength distributions. A comparison with the experimental SD sum rule in ({}^{90})Zr gives one a possibility to check previously estimated (h_{2}^{-}) values which described well the recent combined estimate for (Delta R_{np}) in ({}^{208})Pb and corresponding equation of state parameters – symmetry energy (J_{0}=J(rho_{0})) and a slope parameter (L_{0}=L(rho_{0})).

A measurement of the spin observables in external target and storage ring experiments requires a comparison of interactions of oppositely polarized beams. The ideal way to reduce systematic effects is to store bunches of opposite polarization in the same fill. Here we discuss how such bunches can be organized based on the extended pilot-bunch principle.

The production of polarized (J/psi) mesons at the NICA (Nuclotron based Ion Collider fAcility) energy of (sqrt{s}=27) GeV is studied on the basis of the generalized parton model in the leading order of perturbative QCD. The hadronization of a (cbar{c}) quark pair to a (J/psi) meson is described within the model of nonrelativistic QCD. Nonperturbative model parameters are determined on the basis of a comparison with available experimental data on the production of prompt (J/psi) mesons at the energies of (sqrt{s}=19.4) GeV (NA3) and (sqrt{s}=200) GeV (PHENIX).

Taking into account the recent parameterizations of parton distribution functions (PDFs), the momentum transfer dependence of generalized parton distributions (GPDs) of nucleons is obtained in the limit (xito 0). The gravitational quark and gluon form factors of nucleons are calculated. It is shown that the gluon gravitational radius of the nucleon is comparable to the electromagnetic radius of the proton. The power dependence of form factors is investigated. As a result, it was obtained that the quark gravitational form factor is reproduced by the dipole form, while the form of the gluon gravitation form factor corresponds to the triple form.

Based on the ab initio scheme developed by the authors for calculating the asymptotic characteristics of decay channels of nuclear states—the method of orthogonal functions of cluster channels—an approach has been created that makes it possible to directly implement the results of ab initio calculations of (A)-nucleon wave functions, as well as the partial decay widths of resonant states of compound nucleus obtained through their use, into calculations of cross sections for resonance nuclear reactions. Both calculated and reliably measured resonance energies can be employed in these calculations. Using the examples of such a theoretical analysis of the reaction cross sections for ({}^{7}textrm{Li}(p,{}^{4}textrm{He})^{4})He and ({}^{7}textrm{Be}(n,{}^{4}textrm{He}){}^{4})He, the efficiency of this approach and the wide prospects of its use in nuclear spectroscopy are demonstrated.

An explicit expression for the probability of twisted-photon absorption by an atomic nucleus is obtained. It is found that photoabsorption by nuclei lying in the vicinity of the axis along which a twisted photon propagates obeys the selection rule (jgeqslant|m_{gamma}|), where (m_{gamma}) is the projection of the photon total angular momentum and (j) is the multipolarity of the nuclear transition. In the long-wavelength limit, the (j=|m_{gamma}|) multipole transition makes a dominant contribution to the probability for twisted-photon absorption. The absorption coefficient for twisted photons is found for a target that consists of many nuclei.

The main features of the quasi-frozen spin lattice were calculated in the spinor formalism, such as a spin-tune and a direction of the invariant spin axis. As the radial field perturbations play a crucial role in the EDM measurement procedure, the difference of frozen and quasi-frozen spin lattices was investigated in this regard.

The nuclear tracks created in poly allyl diglycol carbonate (PADC type CR-39) due to exposure to (alpha) particles for specific times followed by chemical etching for definite time periods at 4, 7, 11, and 13 hours are prepared. The measured IR spectrum for investigated films clarified a decrease in peak intensity against increase in etched layer thickness (ELT). This is argued to the formation of free radicals due to etching. Furthermore, pyrolysis of the investigated films displayed that the actual structural variation occurs in the second and third stages of degradation. The calculated activation energy values for thermal decomposition of studied PADC exhibited an increase against etching time periods. Other thermal parameters such as enthalpy, Gibbs free energy, and entropy are calculated and discussed. Moreover, the two nonlinear optical parameters, second-order index of refraction ((n_{2})) and third-order nonlinear optical susceptibility, (chi^{(3)}), are also calculated and displayed that (n_{2}) and (chi^{(3)}) increase by one order of magnitude against the irradiation times which is attributed to the structural damage due to irradiation by (alpha) particle.