Effects In Pair Production Research Articles

Effect of bismuth oxide on the gamma-ray shielding properties of phosphate glass P2O5-Bi2O3-Na2SO4-ZnO in the energy range (0.1–3 MeV)

In this paper, the gamma radiation attenuation parameters were calculated using Phy-X/PSD for a prepared quaternary system of phosphate glass (95-x)P2O5-xBi2O3-3Na2SO4-2ZnO, where (x = 30, 40, and 50 mol%). In addition, the attenuation interactions were calculated using the X-Com program, as all these calculations were done in the range of energies (0.1–3 MeV). The results showed that the S3 sample had the highest value of the mass attenuation coefficient up to the energy value of 0.8261 MeV, after which the values of the three investigated samples were approximately equal. The S3 sample also has the lowest value for a half value layer during the measured range of energy. The results also showed that the photoelectric effect interaction is the largest contributor to the attenuation process at the first three energies (0.1, 0.15, and 0.2 MeV), and at energy values ​​with 0.3–3 MeV, the Compton effect becomes the largest contributor to the attenuation process. The contribution of the pair production effect interaction begins to appear at the energy 1.025 MeV, and its contribution to the gamma ray attenuation process increases gradually in association with the Compton effect interaction until the value of 3 MeV.

Higgs interference effects in top-quark pair production in the 1HSM

We present a next-to-leading-order (NLO) study of the process pp (→ {h1, h2}) →tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document} + X in the 1-Higgs-singlet extension of the Standard Model with an additional heavy Higgs boson h2 that mixes with the light Higgs boson h1. This process is subject to large interference effects between loop-induced Higgs-mediated amplitudes and the QCD continuum background which tend to overcompensate any resonance contributions. A reliable modelling of the resulting top-pair invariant mass shapes requires the inclusion of higher-order QCD corrections, which are presented here. The computation of these NLO corrections is exact in all contributions but in the class of non-factorisable two-loop diagrams which are included in an approximate way such that all infrared singular limits are preserved. We present numerical results for several benchmark points with heavy Higgs masses in the range 700–3000 GeV considering the production of stable top quarks. We find that the interference effects dominate the BSM signal yielding sharp dip structures instead of resonance peaks. The significance and excludability of the BSM effect is explored for the LHC Run 2, Run 3 and HL-LHC.

Improving the pulsed neutron-gamma density method with machine learning regression algorithms

Formation bulk density is one of the critical parameters for formation evaluation. As a safe and environmentally friendly method, the pulsed neutron-gamma density (NGD) measurement is emerging as an alternative to the traditional chemical source-based gamma-gamma density (GGD) measurement. However, in the NGD measurement, the initial energy spectrum, source intensity, and spatial distribution of the secondary inelastic gamma-ray source vary with formation components. Moreover, the energy of inelastic gamma rays is at the MeV level, leading to a non-negligible pair production effect. All these factors affect the accuracy of the bulk-density measurement. In addition, the impact of borehole configuration on NGD is evident, and correction for borehole effects is essential. To improve density accuracy: first, we forgo exploring an explicit theoretical formula for density calculation and instead treat the NGD mathematically as a regression problem and introduce the machine learning regressor, a powerful and popular tool for solving regression problems, into the NGD for the first time; second, we select features less affected by changes in formation chemical composition as input features. Our results show that the final three tuned machine learning regressors selected from the 39 candidate regressors outperform the optimized polynomial model (an optimization of conventional density calculation models) in both accuracy and generalization ability. They complete density prediction and borehole correction in one step, avoiding complex exploration of borehole effects as in the optimized polynomial model and dramatically simplifying the borehole correction process. Moreover, the GaussianProcessRegressor can complete borehole correction without the standoff information and perform well, which is impossible for the optimized polynomial model, broadening application scenarios.

Two Higgs doublets, effective interactions and a strong first-order electroweak phase transition

It is well-known that type II two Higgs doublet models (2HDMs) can struggle to facilitate a strong first-order electroweak phase transition in the early universe whilst remaining theoretically appealing scenarios for many reasons. We analyse this apparent shortfall from the perspective of additional new physics. Starting from a consistent dimension-6 effective field theory Higgs potential extension, we identify the Higgs potential extensions that provide the necessary additional contributions required to achieve a strong first-order electroweak phase transition and trace their phenomenological implications for the Large Hadron Collider. In passing, we critically assess the reliability of the dimension-6 approximation depending on the expected 2HDM phenomenology. In particular, we focus on the role of Higgs pair production (resonant and non-resonant) and interference effects expected in top final states, which are the prime candidates of 2HDM exotics discoveries.

Investigations on Lanthanide polymers for radiation shielding purpose

The current study involves the X-ray/gamma and neutron/EMI shielding and change in mechanical properties of selected lanthanide polymers such as Lanthanum polymer, Cerium polymer, Praseodymium polymer, Gadolinium texaphyrin polymer, Terbium co-ordination polymer and Erbium phosphate hydrate polymer. The X-ray/gamma, neutron and EMI shielding parameters are studied in detail for all the selected polymers. Among all the selected polymers, Erbium phosphate hydrate polymer shows larger values of mass attenuation coefficient, absorption buildup factor, Zeff, Ne, specific absorbed fractions of energy, radiation protection efficiency, kinetic energy released in matter, relative dose, neutron total interaction cross section and absorption cross section values. Furthermore, the EMI shielding parameter (total shielding effectiveness) was also found to be larger for Erbium phosphate hydrate polymer in near infrared, mid infrared, far infrared, ultra high frequency (UHF), very high frequency, high frequency radio waves, middle frequency radio waves, low frequency radio waves and very low frequency radio waves. This clearly indicates that Erbium phosphate hydrate polymer might be used as a good shielding material for X-ray/gamma, neutrons and EMI radiations. We have also reported the change in mechanical properties of the studied lanthanide polymers due to the interaction with X-rays/gamma rays. The mechanical properties remains unchanged in the region where pair production and photoelectric effect dominates. Change in the mechanical properties is observed in the region where Compton scattering dominates, indicating that the change in mechanical properties due to interaction of radiation is also an important parameter while selecting the shielding materials. Present study may be useful in the selection of new shielding material.

Bulk Density Response and Experimental Study of Pulsed Neutron-Gamma Density Logging

The pulsed neutron-gamma density logging technique is used to measure the bulk density of formations based on the detection of gamma rays from the inelastic scattering of neutrons in the formations. However, the induced gamma ray source is regarded as a function of neutron transport and cannot be considered a “point” source. Due to the high energy level of gamma rays, the attenuation of inelastic gamma rays is affected by Compton scattering and pair production. Therefore, bulk density can be measured using inelastic gamma rays while considering the effects of neutron transport and pair production. In this article, a novel density measurement method that uses a completely different response model is proposed to improve the accuracy of density measurement. The process of neutron-gamma density measurement is divided into the neutron transport group and the gamma ray transport group in accordance with the neutron-gamma coupled field theory. A novel density estimation algorithm is derived from the diffusion equation and the gamma ray attenuation law. The accuracy and specification of density measurement are investigated through the Monte Carlo simulation and the calibration of test pits. Theoretical and experimental analyses show that the neutron transport and gamma ray transport are not entirely independent of each other in the pulsed neutron-gamma density measurement. The newly developed model can effectively enable the inelastic gamma rays to conform to the gamma ray attenuation law and keep the measurement accuracy at ±0.025 g/cm3. Moreover, neutron-gamma density is insensitive to the porosity and lithology of the formation. The proposed novel algorithm successfully establishes the calculation model for the relationship between inelastic gamma rays and bulk density, providing a new perspective for density measurement in pulsed neutron-gamma density logging.

Mathematical calculation of gamma rays interaction in bismuth gadolinium silicate glass using WinXCom program

The WO3 doped bismuth gadolinium silicate glass have been calculated using WinXCom program at the gamma energy range of 1 keV to 100 GeV in the concentration of WO3 = 0, 10, 20 and 30 mol%. The mass attenuation coefficient, the partial interaction and effective atomic number were investigated. The results of the photoelectric absorption, the μm and the Zeff show the similar trend and the absorption edges were observed at an energy lower than 100 keV. The result can be found the photoelectric absorption at low photon energy, the Compton scattering in the medium photon energy and the pair production effect has the main interaction at high photon energy. Furthermore, the Zeff show increasing the concentration of WO3 the values because of the atomic number of W replacing Si in the glass matrix.

Possible Neutrino-Antineutrino Production during Gamma Ray e−e+ Pair Production: Monte Carlo Simulation Study

An alternative Feynman diagram for electron-positron pair production, in which neutrino and antineutrino are also produced on the same pathway, is introduced here. In the proposed pair production process, a portion of the momentum is carried by neutrinos and antineutrinos, allowing the rest of the momentum for the electron-positron pair. Simulations to inspect the proposed pair production process were conducted in this research using the EGS5 code system while modifying its subroutine “PAIR”. Liquid Xenon detector was then positioned in the path of various mono-energetic photon beams ranging from 2.6 to 12 MeV. These simulations were intended to inspect the detectability of the alternative pair production effects on radiation measurements in order to assess the detection conditions. Simulation results provided a comparison between the original pair production process and the proposed pair production process. Spectral results showed that changes in the region around 1 - 2 MeV and in the photopeak region were remarkable, therefore detectable. Further experimental research is recommended based on simulation findings. The alternative pair production process, firstly introduced in this paper, led to production of a larger flux of neutrinos from gamma radiation. This additional neutrino production and its contribution to non-baryonic dark matter are discussed.

Nuclear Adiabatic Effects of Electron-Positron Pairs on the Dynamical Instability of Very-Massive Stars

The adiabatic effects of electron-positron pair-production on the dynamical instability of very-massive stars is investigated from stellar progenitors of carbon-oxygen cores within the range of 64 M < MCO < 133 M both with and without rotation. At a very high temperature and relatively low density; the production of electron-positron pairs in the centres of massive stars leads the adiabatic index to below 4/3. The adiabatic quantities are evaluated by constructing a model into a thermodynamically consistent electron-positron equation of state (EoS) table. It is observed that the adiabatic indices in the instability regions of the rotating models are fundamentally positive with central temperature and density. Similarly, the mass of the oxygen core within the instability region has accelerated the adiabatic indices in order to compress the star, while the mass loss and adiabatic index in the non-rotating model exponentially decay. In the rotating models, a small amount of heat is required to increase the central temperature for the end fate of the massive stars. The dynamic of most of the adiabatic quantities show a similar pattern for all the rotating models. The non-rotating model may not be suitable for inducing the instability. Many adiabatic quantities have shown great effects on the dynamical instability of the massive stars due to electron-positron pair-production in their centres. The results of this work would be useful for better understanding of the end fate of very-massive stars.

Polarized QED cascades

By taking the spin and polarization of the electrons, positrons and photons into account in the strong-field QED processes of nonlinear Compton emission and pair production, we find that the growth rate of QED cascades in ultra-intense laser fields can be substantially reduced. While this means that fewer particles are produced, we also found them to be highly polarized. We further find that the high-energy tail of the particle spectra is polarized opposite to that expected from Sokolov–Ternov theory, which cannot be explained by just taking into account spin-asymmetries in the pair production process, but results significantly from ‘spin-straggling’. We employ a kinetic equation approach for the electron, positron and photon distributions, each of them spin/polarization-resolved, with the QED effects of photon emission and pair production modelled by a spin/polarization dependent Boltzmann-type collision operator. For photon-seeded cascades, depending on the photon polarization, we find an excess or a shortage of particle production in the early stages of cascade development, which provides a path towards a controlled experiment. Throughout this paper we focus on rotating electric field configuration, which represent an idealized model and allows for a straightforward interpretation of the observed effects.

Regularization, renormalization and consistency conditions in QED with x-electric potential steps

The present article is an important addition to the nonperturbative formulation of QED with x-steps presented by Gavrilov and Gitman (Phys. Rev. D. 93:045002, 2016). Here we propose a new renormalization and volume regularization procedures which allow one to calculate and distinguish physical parts of different matrix elements of operators of the current and of the energy–momentum tensor, at the same time relating the latter quantities with characteristics of the vacuum instability. For this purpose, a modified inner product and a parameter tau of the regularization are introduced. The latter parameter can be fixed using physical considerations. In the Klein zone this parameter can be interpreted as the time of the observation of the pair-production effect. In the refined formulation of QED with x-steps, we succeeded to consider the back-reaction problem. In the case of an uniform electric field E confined between two capacitor plates separated by a finite distance L, we see that the smallness of the back-reaction implies a restriction (the consistency condition) on the product EL from above.

Gamma-ray shielding properties of lead borovanadate glasses

The gamma-ray shielding properties for the xPbO‧50B2O3‧(50-x)V2O5 glass systems (where x varied between 20 and 49 mol%) were investigated. The photon attenuation factors were determined using Phy-X/PSD software to evaluate the influence of PbO on the radiation shielding ability of the glass. The mass attenuation coefficient (MAC) increased with the addition of PbO. We discussed the effects of photoelectric effect, Compton scattering and pair production on the MAC values at different energy regions. The highest half value layer (HVL) for the investigated borovanadate glasses was reported at 284 keV and lie within the range of 0.5067 and 0.931 cm. The sample containing the highest content of PbO (49 mol%) had the lowest HVL, which indicates that it is the most effective radiation shield among the tested borovanadate glasses. The tenth value layer (TVL) results revealed that the shielding ability for the borovanadate glasses improved when the percentage of PbO increased from 20 to 49 mol%. The least TVL values of the samples with 20 and 49 mol% of PbO were 1.682 cm at 284 keV and 2.432 cm at 347 keV.

Enhanced dose measurement of zinc oxide nanoparticles by radiochromic polymer dosimeter and Monte Carlo simulation.

The aim of this study is to evaluate the effects of Zinc Oxide nanoparticles on dose enhancement factor using PRESAGE dosimeter and Monte Carlo simulation. High Z materials absorb X-ray remarkably. Among Nano-science, Zinc Oxide nanoparticles are interesting semiconductors, producing reactive oxygen species when irradiated by photons. Therefore, it seems that dose enhancement originating by incorporating ZnO NPs in irradiated volume would increase the therapeutic ratio. Initially, the PRESAGE dosimeter was fabricated and calibrated. Then Zinc Oxide nanoparticles with an average particle size of about 40 nm were synthesized. At next step, various concentrations of the nanoparticles were incorporated into the PRESAGE composition and irradiated in radiation fields. Then, the mentioned processes were simulated. Practical measurements revealed that by incorporating 500, 1000 and 3000 μg ml-1 ZnO NPs into PRESAGE the dose enhancement factor of 1.36, 1.39, 1.44 for 1 × 1 cm 2 field size, 1.39, 1.41, 1.46 for 2 × 2 cm 2 and 1.40, 1.45 and 1.50 for 3 × 3 cm 2 could be found, respectively. Simulation results showed that in the mentioned condition, the dose enhancement factor of 1.05, 1.08, 1.10 for 1 × 1 cm 2 field size, 1.06, 1.09, 1.10 for 2 × 2 cm 2 and 1.08, 1.11 and 1.13 for 3 × 3 cm 2 could be derived, respectively. The results of this study showed that dose enhancement increases by increasing concentration of Zinc Oxide nanoparticles. Many reasons such as photoelectric, pair production effects and even Compton scattering can cause dose enhancement for megavoltage beams.

Polarization effects in bound-free pair production

We present a theoretical study of bound-free electron-positron pair production in the interaction of $\gamma$-rays with bare ions. Special attention is paid to the longitudinal polarization of both the emitted positrons and the produced hydrogen-like ions. To evaluate this polarization we employed exact solutions of the relativistic Dirac equation and treat the electron-photon coupling within the framework of first-order perturbation theory. Detailed calculations have been performed for both, low- and high-Z ions and for a wide range of photon energies. The results of these calculations suggest that bound-free pair production can be a source of strongly polarized positrons and ions.

Very high-energy constraints on the infrared extragalactic background light

Context. Measurements of the extragalactic background light (EBL) are a fundamental source of information on the collective emission of cosmic sources. Aims. At infrared wavelengths, however, these measurements are precluded by the overwhelming dominance from interplanetary dust emission and the Galactic infrared foreground. Only at λ > 300 μm, where the foregrounds are minimal, has the infrared EBL (IR EBL) been inferred from analysis of the COBE maps. The present paper aims to assess the possibility of evaluating the IR EBL from a few micrometers up to the peak of the emission at > 100 μm using an indirect method that avoids the foreground problem. Methods. To this purpose we exploit the effect of pair-production from gamma-gamma interaction by considering the highest-energy photons emitted by extragalactic sources and their interaction with the IR EBL photons. We simulate observations of a variety of low-redshift emitters with the forthcoming Imaging Atmospheric Cherenkov Telescope (IACT) arrays (CTA in particular) and water Cherenkov observatories (LHAASO, HAWC, SWGO) to assess their suitability to constrain the EBL at such long wavelengths. Results. We find that even under the most extremely favorable conditions of huge emission flares, extremely high-energy emitting blazars are not very useful for our purpose because they are much too distant (> 100 Mpc the nearest ones, MKN 501 and MKN 421). Observations of more local AGNs displaying very high-energy emission, like low-redshift radio galaxies (M 87, IC 310, Centaurus A), are better suited and will potentially allow us to constrain the EBL up to λ ≃ 100 μm.

Laser pulse-length effects in trident pair production

Laser pulses facilitate multiphoton contributions to the trident pair production , where the label L indicates a laser field dressed electron (e−) or positron (e+ ). We isolate the impact of the pulse envelope in the trident S matrix element, formulated within the Furry picture, in leading order of a series expansion in the classical nonlinearity parameter a0. Generally, the Fourier transform of the envelope carries the information on the pulse length, which becomes an easily tractable function in the case of a pulse envelope. The transition to a monochromatic laser wave can be handled in a transparent manner, as also the onset of bandwidth effects for short pulses can be factorized out and studied separately.

Reconstruction of top-quark mass effects in Higgs pair production and other gluon-fusion processes

We propose a novel method for the treatment of top-quark mass effects in the production of H(∗), HH, HZ and ZZ final states in gluon fusion. We show that it is possible to reconstruct the full top-quark mass dependence of the virtual amplitudes from the corresponding large-mt expansion and the non-analytic part of the amplitude near the top-quark threshold ŝ = 4mt2 with a Padé ansatz. The reliability of our method is clearly demonstrated by a comparison with the recent NLO result for Higgs pair production with full top-quark mass dependence.

Ponderomotive effects in multiphoton pair production

The Dirac-Heisenberg-Wigner formalism is employed to investigate electron-positron pair production in cylindrically symmetric but otherwise spatially inhomogeneous, oscillating electric fields. The oscillation frequencies are hereby tuned to obtain multiphoton pair production in the nonperturbative threshold regime. An effective mass as well as a trajectory-based semi-classical analysis are introduced in order to interpret the numerical results for the distribution functions as well as for the particle yields and spectra. The results, including the asymptotic particle spectra, display clear signatures of ponderomotive forces.

Non-resonant and electroweak NNLO correction to the e+e\u2212 top anti-top threshold

We determine the NNLO electroweak correction to the {e}^{+}{e}^{-}to boverline{b}{W}^{+}{W}^{-}X production cross section near the top-pair production threshold. The calculation includes non-resonant production of the final state as well as electroweak effects in resonant top anti-top pair production with non-relativistic resummation, and elevates the theoretical prediction to NNNLO QCD plus NNLO electroweak accuracy. We then study the impact of the new contributions on the top-pair threshold scan at a future lepton collider.

BCM-2.0 – The new version of computer code “Basic Channeling with Mathematica©”

The new symbolic-numerical code devoted to investigation of the channeling phenomena in periodic potential of a crystal has been developed. The code has been written in Wolfram Language taking advantage of analytical programming method. Newly developed different packages were successfully applied to simulate scattering, radiation, electron-positron pair production and other effects connected with channeling of relativistic particles in aligned crystal. The result of the simulation has been validated against data from channeling experiments carried out at SAGA LS.