Cross Sections For Creation Research Articles

Гипотеза о контракции калибровочной группы Стандартной модели и экспериментальные данные БАК

Within the framework of the contraction hypothesis of the
 gauge group of the Standard Model, the behavior of the amplitude
 of the dominant Higgs boson production process in the
 four-lepton decay with an increasing temperature T is analyzed.
 It is shown that the modified process breaks down into
 a number of channels depending on the contribution of the
 color components in the loop of virtual quarks, leading to the
 creation of the Higgs boson. The dependence on T of the cross
 section of each channel is found. Comparison with LHC data
 on Higgs boson creation cross sections at energies (temperatures)
 of 7, 8, 13, and 14 TeV showed that the hypothesis about
 the contraction of the gauge group of the Standard Model does
 not contradict these data.

Diagnostics of peak laser intensity by pair production from thin foil target

It is known that in the small quantum parameter regime the Breit-Wheeler electron-positron pair creation cross section is extremely sensitive on the photon energy and on the background field. We present the dependence of positron yield on laser intensity in laser-foil interactions with the help of analytical theory and particle-in-cell simulaitons. These particles are emitted in a relatively narrow range of cone angles close to perpendicular direction relative to the laser beam axis. This allows for establishing an in situ intensity diagnostic by measuring the positron current in experiments where peta-watt class lasers are used.

The possibility to study in-medium modification of J/ψ mesons from their photoproduction on nuclei near threshold in the case of presence of the LHCb pentaquark states [formula omitted], [formula omitted] and [formula omitted] in this photoproduction

We study the J/ψ photoproduction from nuclei in the near-threshold beam energy region of Eγ=5–11 GeV within the nuclear spectral function approach by considering incoherent direct (γN→J/ψN) and two-step (γp→Pc+(4312), Pc+(4312)→J/ψp; γp→Pc+(4440), Pc+(4440)→J/ψp; γp→Pc+(4457), Pc+(4457)→J/ψp) J/ψ production processes. We calculate the absolute excitation functions for the non-resonant and resonant production of J/ψ mesons off 12C and 208Pb target nuclei within the different scenarios for in-medium modification of the directly photoproduced J/ψ mesons and for branching ratios of the decays Pc+(4312)→J/ψp, Pc+(4440)→J/ψp and Pc+(4457)→J/ψp. We show that the non-resonant subthreshold J/ψ production in γA reactions reveals some sensitivity to employed in-medium modification scenarios for J/ψ mesons, which is not masked by the resonantly produced J/ψ mesons, only if above branching ratios are less than 5%. We also demonstrate that if these branching ratios more than 5% then the presence of the Pc+(4312), Pc+(4440) and Pc+(4457) resonances in J/ψ photoproduction on nuclei produces above threshold additional enhancements in the behavior of the total J/ψ creation cross section on nuclei, which could be also studied in the future JLab experiments at the CEBAF facility to provide both further evidence for their existence and valuable information on their nature.

The role of hidden-charm pentaquark resonance [formula omitted] in J/ψ photoproduction on nuclei near threshold

We study the J/ψ photoproduction from nuclei at near-threshold incident photon energies of 5–11 GeV within the nuclear spectral function approach by considering incoherent direct (γN→J/ψN) and two-step (γp→Pc+(4450), Pc+(4450)→J/ψp) photon–nucleon charmonium creation processes. We calculate the absolute and relative excitation functions within the different scenarios for in-medium modification of the directly photoproduced J/ψ mesons. We show that the overall subthreshold J/ψ production in γA reactions reveals some sensitivity to adopted in-medium modification scenarios for J/ψ mesons only if branching ratio Br[Pc+(4450)→J/ψp] ∼ 1% and less. Our studies also demonstrate that the presence of the Pc+(4450) resonance in J/ψ photoproduction produces above threshold additional enhancements in the behavior of the total J/ψ creation cross section on nuclei, which could be also studied in the future JLab experiments at the upgraded up to 12 GeV CEBAF facility to provide further evidence for its existence.

Contribution of Delbrück scattering to the refractive index of substances at mega-electronvolt photon energies

Recent work by Habs et al. [1] posits that for MeV photons, the contribution of Delbrück scattering to the refractive index of a substance δD becomes dominant as compared with the ordinary polarization contribution due to free electrons. Using the same method suggested Habs et al., we have calculated the contribution of Delbrück scattering using the dispersion relation between δD and the pair creation cross section in the nuclear Coulomb field σp. We have also considered the corrections related to the near-threshold behavior of σp and estimated the contribution of higher-order Delbrück scattering corrections. Our results indicate that δD for MeV photons is small and cannot be responsible for making the index of refraction for silicon larger than unity.

The creation, destruction, and transfer of multipole moments in electron- and proton-impact ionization of atoms and ions

Expanding on previous works that involved elastic and inelastic scattering of electrons by atoms and ions, we use the wave-packet propagation scheme of Dollard to define multipole moment creation, destruction and transfer cross sections for electron- and proton-impact ionization of atoms and ions. The electron-impact cross sections can then be used by defining appropriate rate coefficients for use in Fujimoto’s population-alignment collisional-radiative model for cylindrically symmetric plasmas. Our result for the alignment creation cross section is in agreement with those formulae that were obtained earlier intuitively or by semi-classical collisional methods. The multipole cross sections obtained here can be used also for modelling the relaxation behaviour of laser-excited plasmas under cylindrical symmetry conditions. We have also derived the electron- and proton-impact ionization multipole cross sections in terms of Liouville-space quantities, which then enabled us by using group theoretical methods to obtain the azimuthal-angle dependence of the multipole cross sections and symmetry properties that are results of reflection across a plane over the collisional axis.

Cross sections for meson–meson nonresonant reactions

Meson–meson nonresonant reactions governed by the quark-interchange mechanism are studied in a potential that is derived from QCD. S-wave elastic phase shifts for I = 2 ππ and I = 3 / 2 Kπ scattering are obtained with wave functions determined by the central spin-independent term of the potential. The reactions include inelastic scatterings of two mesons in the ground-state pseudoscalar octet and the ground-state vector nonet. Cross sections for reactions involving π, ρ, K and K * indicate that mesonic interactions in matter consisting of only K and K * can be stronger than mesonic interactions in matter consisting of only π and ρ and the reaction of I = 3 / 2 π K * → ρ K is most important among the endothermic nonresonant reactions. By the quark-interchange mechanism we can offer s -dependences of ϕ absorption cross sections in collisions with π and ρ and relevant average cross sections what are very small for the reaction of I = 1 π ϕ → K * K * and remarkably large for the reaction of I = 1 ρ ϕ → K * K * . It is found from the s -dependences of cross sections that ρ and K * creation cross sections can be larger than their absorption cross sections, respectively.

Distorted wave Born approximation calculation of pair production cross section for 12.5 MeV photon

We present in this communication the theoretical results of our calculation in distorted wave Born approximation (DWBA) in point Coulomb potential of the differential and total electron-positron pair production cross section by 12.5 MeV photons on different targets ( Z = 1 , 30, 50, 68, 82 and 92). We also present differential pair production cross-section in the tip region ( E - = 1.008 mc 2 ) for photon energies 5.0–40.0 MeV for a large number of targets. We compare the interpolated DWBA pair production cross section with the experimental electron-positron pair creation cross section in the energy range 5.0–12.5 MeV on Ta and Bi.

Brane factories

We propose that higher-dimensional extended objects (p-branes) are created by super-Planckian scattering processes in theories with TeV scale gravity. As an example, we compute the cross section for p-brane creation in a (n+4)-dimensional spacetime with asymmetric compactification. We find that the cross section for the formation of a brane which is wounded on a compact submanifold of size of the fundamental gravitational scale is larger than the cross section for the creation of a spherically symmetric black hole. Therefore, we predict that branes are more likely to be created than black holes in super-Planckian scattering processes in these manifolds. The higher rate of p-brane production has important phenomenological consequences, as it significantly enhances possible detection of non-perturbative gravitational events in future hadron colliders and cosmic rays detectors.

Fluorescence of low-lying doubly photoexcited states in helium

In this work we investigate fluorescence decay of low-lying $(n<~8)$ resonances with odd parity and total angular momentum $J=1$ below the $N=2$ threshold of helium. After discussing the photoabsorption cross section for creation of such states, we estimate the probability for the primary fluorescence transition to $1snl$ states below the first ionization threshold. The subsequent fluorescence cascade decay brings helium into the ground state or into one of the two long lived $1s2s{}^{1,3}S$ states. We discuss the time scale of the cascade and combine all the calculated transition probabilities to determine branching ratios for singlet and triplet metastable production. Finally, we estimate the angular distribution of the emitted uv photons and perform a comparison with the recent experimental data of Penent et al. [Phys. Rev. Lett. 86, 2758 (2001)].

Hidden crossing superpromotion mechanism for -vacancy creation in heavy ion - atom collisions

It is shown that the transitions along the - and -superseries of hidden crossings in a heavy ion - atom collision system (, - 30) form a dominant mechanism for the vacancy production at low reduced relative collision velocities. The -vacancy creation probability as a function of the impact parameter, calculated within this model for several collision systems and collision energies, agrees well with the experimental observations. A scaling relationship is derived for the -vacancy creation cross section which adequately describes the experimental data for charge-symmetric heavy ion - atom systems.

Defect Creation by Electronic Processes in MgO Bombarded with GeV Heavy Ions

AbstractTo study the defect creation induced by electronic processes in refractory oxides, MgO single crystals were irradiated with high energy tin, uranium and lead ions. Optical absorption measurements showed that F-type centers (oxygen vacancies with trapped electrons) were created during irradiation. The total number of centers per unit area of bombarded sample increases linearly with irradiating fluence. The main part of the point defects was found to arise from electronic processes. The concentration of F-type centers induced by ionization increases with the electronic energy losses. Assuming a saturation of point defect concentration at high fluences, F-type center creation cross sections could be estimated. The influence of irradiation temperature and of the velocity of the bombarding ions are discussed.

Creation of massive particles in high energy scattering of electrons on atoms

The cross section for creation of scalar, pseudoscalar, vector and axial vector massive particles in high energy collisions of electrons on atoms is obtained.

Electron-pair creation on uranium by 10 and 20 MeV photons.

Improved corrections for inscattering and photon regeneration were made to observed total absorption cross sections of uranium reported earlier. Electron-pair creation cross sections ${\ensuremath{\sigma}}_{K}$ for 10 and 20 MeV photons on $^{238}\mathrm{U}$ were obtained from the adjusted total cross sections. Recently published theoretical values of ${\ensuremath{\sigma}}_{K}$ at these energies agree within about 1% with the revised experimental values. The discrepancy at 10 MeV was previously thought to be about 4%. The remaining discrepancy may be due to neglect of the finite size of the nucleus in the calculations, or to slightly inaccurate screening or radiative corrections.

The K-Shell Population of Ions Penetrating Ferromagnetic Solids

K-vacancy fractions as well as cross sections for creation and quenching of K-vacancies have been measured for O, F, Mg, Si, and S projectiles moving through solid Fe, Co, Ni and Gd at velocities ranging from 1.5v0 to 10.5v0. Two different techniques were used, i.e., the beam-X-ray and the probe-layer method, respectively. Based on comparisons with semiempirical estimates a number of different K-shell processes were identified. Direct Coulomb ionization and excitation and electron capture dominate at high velocities, whereas collision-perturbed deexcitation and quasi-molecular effects are important at low velocities. Distinct level-swapping effects are observed for O and F in Fe. The present data provide the basis for an investigation of the origin of the transient magnetic field in a recent paper.

Creation of relativistic fermionium in collisions of electrons with atoms.

The cross section for creation of bound states of a fermion and an antifermion, fermionium, in high-energy collisions of electrons with atoms is calculated. Applications to positronium and to bound states of a muon and an antimuon, \ensuremath{\mu} fermionium, are discussed.

K-Shell Cross Sections Extracted from Measured Charge-State Distributions for F and Si Ions Penetrating C

Charge-state distributions have been measured as a function of foil thickness and incident projectile charge state for 4.5-9.0 v0. F ions and 6.0-9.0 v0 Si ions transmitted through thin carbon foils. The charge-state distributions are analyzed in terms of separate K- and outer-shell populations. The outer-shell population is demonstrated to depend on the number of K vacancies in the ion. The ionic K-shell population inside the solid is described in a three-component model, and cross sections for creation and quenching of single and double K vacancies were extracted from a fit to the data. Based on these cross sections, different types of interactions involving the ionic K shell inside solid carbon could be identified: electron excitation and ionization, electron capture, and spontaneous decay of outer-shell electrons.

Theory of neutron scattering by excitons

Using neutron sources giving particles with energies of a few electron volts it is possible that the dispersion of exciton energy bands could be measured directly. Estimates of the cross sections for creation of excitons of both the Frenkel and Wannier type are given. The former give values similar to those for spin wave or electronic transitions but the electronic form factor makes these very small if the momentum transfer Q lies outside the first Brillouin zone. For Wannier excitons the cross section is always reduced by a factor giving the probability that the electron-hole pair are confined to the same atom. At large Q a process via the creation of virtual phonons gives a larger cross section is always reduced by a factor giving the probability that the electron-hole pair are confined to the same atom. At large Q a process via the creation of virtual phonons gives a larger cross section since it avoids the electronic form factor.

Application of Landau-Zener Formula for the Ratios of Target to Projectile K-Shell Vacancy Production

The target ( Z 2 ) and projectile ( Z 1 ) K -shell vacancy creation cross sections were measured from high energy collisions of Ni and Br ions with various targets. The ratio of these cross sections was fitted to the formula deduced from the work of Landau and Zener. This formula is expressed in a simple form and depends only on the incident velocity and charges of target and projectile ions, although it contains a single parameter. By varying this parameter an excellent agreement was obtained.

Stark Beats in Lyman-Series Emission

Observed intensity fluctuations in the emission of Stark-perturbed $\mathrm{L}\mathrm{y}\ensuremath{-}\ensuremath{\beta}$ radiation, from hydrogen atoms formed by passage of hydrogen ions through carbon foils, are compared with theoretical calculations using a density-matrix formalism to yield information on the cross sections for creation into the various $l$ states. It is found, for beam energies between 250 and 500 keV/atom, that the $s$ states are preferentially populated by more than a factor of 4, compared to a statistical distribution. Similar results are also obtained for $\mathrm{L}\mathrm{y}\ensuremath{-}\ensuremath{\alpha}$ emission in electric and motional electric fields, in contrast with previous reports at lower energies. The effects of Zeeman splittings, hyperfine interaction, and fringing fields on the signal are investigated.