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Background: Despite recommendations to use syringe and vial shields to reduce exposure of the hands of staff when manipulating PET radiopharmaceuticals, operators sometimes prefer to work without shields, believing that the faster handling limits the equivalent dose. The aim of this work is to show that this approach does not properly consider the contribution of positrons to the dose., Materials and Methods: Using the Varskin+ code, skin doses were calculated for syringes of various sizes, filled with 18 F, 11 C or 68 Ga solution. Syringes without shielding, or shielded with 2 mm and 10 mm of tungsten were considered., Results: Dose rate values in mSv/s per MBq, averaged on a 1 cm 2 surface at a depth of 0.07 mm were calculated for all the above conditions. For example, in the case of 3 mL 18 F syringe at 1 mm from the skin, the dose rate without shielding is 1.32E-02 and 8.63E-04 for positrons and photons respectively. For 11 C, the corresponding dose rates are 4.70E-02 and 8.90E-04 respectively, and for 68 Ga, 8.52E-02 and 9.48E-04., Conclusions: Our results show that the dose due to positrons is the principal component of skin irradiation, by a factor of 3-100, depending on the conditions. The use of shields for syringes and vials is necessary to avoid unjustified skin exposures, that may challenge dose limits. In our opinion, automatic systems for dispensing and allowing injection with shielded syringes, or automatic injectors, are economically justified and should be adopted in PET., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The precision measurements of the cosmic-ray positron and electron fluxes collected by the Alpha Magnetic Spectrometer on the International Space Station during first ten years of operations are presented. The positron flux exhibits complex energy dependence. It is described by the sum of a term associated with the positrons produced in the collision of cosmic rays, which dominates at low energies, and a new source term, which dominates at high energies and is associated with either dark matter or astrophysical origin. The positron source term also manifest itself in the measured electron spectrum. This is the first indication of the existence of an identical charge symmetric source term both in the positron and in the electron spectra. If confirmed with a higher level of confidence, these observations might suggest the existence of new physics. [ABSTRACT FROM AUTHOR]

We here report theoretical triply differential cross sections (TDCS) for 250 eV electron and positron impact ionization of the methane molecule calculated within the second-order distorted-wave Born approximation (DWBA2) for various momentum transfer conditions. The experimental data taken from Işık et al. [J. Phys. B: At., Mol. Opt. Phys. 49, 065203 (2016)] will be compared with the current theoretical predictions as well as molecular three body distorted wave (M3DW) approximation and generalized Sturmian function (GSF) theoretical models in a non-coplanar geometry. In the low analyzer scattering plane, the results obtained within the DWBA2 theory show better agreement with the experimental results compared to the GSF results. The M3DW results also exhibit agreement with the experimental results, in particular in the perpendicular plane geometry. Furthermore, significant differences between electron and positron TDCS were observed. [ABSTRACT FROM AUTHOR]

It is shown that electromagnetic interactions of cosmic ray protons provide a noticeable contribution to positrons production. This is due to a combination of low energy threshold of electron–positron pair creation compared to the thresholds of pion creation in strong interactions and rapid decrease of the cosmic rays energy spectrum. Moreover, the electromagnetically produced positrons are very soft, therefore their annihilation with background electrons directly produces the observed 511 keV gamma-line. [ABSTRACT FROM AUTHOR]

The dissemination of positron-acoustic (PA) nonlinear structures, including the solitary waves (SWs) and cnoidal waves (CWs), is analyzed in an unmagnetized electron–positron–ion (e–p–i) plasma having inertial cold positrons and inertialess Cairns distributed electrons and Maxwellian positrons as well as immobile positive ions. The reductive perturbation method (RPM) is introduced to reduce the fluid equations to this model to the Korteweg–de Vries (KdV) type equation for studying small amplitude PA waves (PAWs). Moreover, the Kawahara (sometimes called the fifth-order KdV) equation is also obtained to investigate the characteristics of large amplitude PAWs. The effects of related parameters, such as nonthermal parameters, hot positron concentration, electron concentration, and temperature ratios, are numerically examined on the features of SWs and CWs. [ABSTRACT FROM AUTHOR]

Energetic positrons have been observed in the interstellar medium, and high-energy positrons with relativistic energies up to approximately 1 TeV have been detected in Galactic cosmic rays. We conducted a study on the acceleration of particles, specifically positrons, in a nonrelativistic quasi-parallel collisionless shock induced by a plasma consisting of protons, electrons, and positrons. The positron-to-proton number density ratio in the plasma is 0.1. We focused on a representative shock with a sonic Mach number of 17.1 and an Alfvénic Mach number of 16.8 in the rest frame of the shock. To investigate the acceleration mechanisms of particles including positrons in the shock, we utilized 1D particle-in-cell simulations. It was found that all three species of particles in the shock can be accelerated and exhibit power-law spectra. At the shock front, a significant portion of incoming upstream particles are reflected and undergo significant energy increases, and these reflected particles can be efficiently injected into the process of diffusive shock acceleration (DSA). Moveover, the reflected positrons can be further accelerated by an electric field parallel to the magnetic field when they move along the magnetic field upstream of the shock. As a result, positrons can be preferentially accelerated to be injected in the DSA process compared to electrons. [ABSTRACT FROM AUTHOR]

The research of the electron and positron spectrum of galactic cosmic rays is an important task of high-energy astrophysics. The necessity of using new methods of electron and positron registration is caused by insufficient statistical reliability of data from modern experiments in the TeV energy range. In the present work, one of the possible registration methods based on the use of synchrotron radiation of electrons and positrons in the Earth's magnetic field is investigated. Using modeling of trajectories of high-energy electrons, positrons, and synchrotrons photons emitted by them, the detector count rate for the ISS and ROS orbits has been estimated. The possibility of separation of electrons and positrons using this method is shown. [ABSTRACT FROM AUTHOR]

It is found that the polarity reversal phenomenon occurs in the nanosecond pulse breakdown experiment. Two-dimensional axisymmetric particle-in-cell/Monte Carlo collisions' calculation is used to observe energetic electrons at positive nanosecond pulse voltage in atmospheric air and compared with previous calculation results under negative polarity in an attempt to explain the polarity reversal phenomenon. During the evolution of the positive polarity discharge, the difference in spatial net charge distribution leads to distortion of the electric field, which makes the electric field in the area of the ionization channel head very high, exceeding the threshold at which electrons can enter the high-energy state. The simulation results show that although electrons travel in the opposite direction to the ionization channel, energetic electrons can also be generated during the positive polarity discharge's evolution, which may differ from what some researchers expected. However, it is also found that the maximum energy of energetic electrons under positive nanosecond pulse voltage is lower than that under negative nanosecond pulse voltage (only about 1/4). This may be mainly because in the case of positive polarity, the energetic electrons in the head of the ionization channel will move to the low-field intensity region inside the ionization channel and cannot be accelerated continuously. However, it must be pointed out that in the case of positive polarity, energetic electrons still contribute significantly to the rapid breakdown of the air gap. This study provides a deeper understanding of the physics of nanosecond pulse discharge. [ABSTRACT FROM AUTHOR]

A quadruple Beltrami (QB) equilibrium state for a four-component plasma that consists of inertial electrons, positrons, lighter positive (H+) ions and heavier negative ions O 2 − is derived and investigated. The QB relaxed state is a linear superposition of four distinct single Beltrami fields and provides the possibility of the formation of four self-organized vortices of different length scales. In addition, robust magnetofluid coupling characterizes this non-force-free state. The analysis of the QB state also shows that by adjusting the generalized helicities and densities of plasma species, the formation of multiscale structures as well as the paramagnetic and diamagnetic behavior of the relaxed state can be controlled. [ABSTRACT FROM AUTHOR]

We present ionization cross sections of hydrogen molecules by electron and positron impact for impact energies between 20 and 1000 eV. A three-body Classical Trajectory Monte Carlo approximation is applied to mimic the collision system. In this approach, the H2 molecule is modeled by a hydrogen-type atom with one active electron bound to a central core of effective charge with an effective binding energy. Although this model is crude for describing a hydrogen molecule, we found that the total cross sections for positron impact agree reasonably well with the experimental data. For the electron impact, our calculated cross sections are in good agreement with the experimental data in impact energies between 80 eV and 400 eV but are smaller at higher impact energies and larger at lower impact energies. Our calculated cross sections are compared with the scaled cross sections obtained experimentally for an atomic hydrogen target. We also present single differential cross sections as a function of the energy and angle of the ejected electron and scattered projectiles for a 250 eV impact. These are shown to agree well with available data. Impact parameter distributions are also compared for several impact energies. [ABSTRACT FROM AUTHOR]

Nonlinear ion-acoustic solitary and shock waves were analysed in a system of collisionless, dissipative and magnetised multicomponent plasma. The system was made up of a fluid of inertial ions, electrons that were distributed superthermally and positrons. Korteweg–de Vries–Burgers (KdVB) equation was produced when the reductive perturbation approach was used to evaluate the plasma system nonlinearly. The tanh method was used to find the analytical solution of the derived KdVB equation. The study demonstrated that the superthermal parameters, magnetic field direction, ion kinematic viscosity and positron and electron concentration all affect the oscillatory shock wave features such as speed, amplitude and width. On the other hand, the bifurcation analysis showed that the equilibrium point produces an unstable spiral source as the Burgers term increases and that it transforms into a nodal source with any further increase in the Burgers term. The present results are helpful for understanding collective phenomena and the stability criterion of ion-acoustic (IA) solitary and shock waves in magnetoplasmas with superthermal electrons and positrons, which are observed in some astrophysical environments, like the interstellar medium. [ABSTRACT FROM AUTHOR]

This paper comprehensively investigates the oblique propagation of ion-acoustic solitary waves (IASWs) with arbitrary amplitude in a magnetoplasma consisting of inertialess non-Maxwellian (nonthermal) electrons, inertialess Maxwellian positrons, and inertial adiabatically heated ions. It is postulated that the positive ions demonstrate adiabatic behavior that is distinguished by anisotropic thermal pressure. The study utilizes Sagdeev's pseudopotential theory to analyze the fluid equations of the plasma model and reduce them to the energy equation. Different plasma configuration factors, such as nonthermal parameters, positron concentration, and parallel and perpendicular ion pressure, are being studied to see how they affect the properties of solitary waves with large amplitudes. The findings demonstrate the simultaneous coexistence of compressive and rarefactive IASWs, significantly influenced by positrons and nonthermal electron parameters. The study provides valuable insights into wave phenomena in magnetized plasmas and presents possible applications in both Space and laboratory plasma environments. [ABSTRACT FROM AUTHOR]

We show that two positrons can form a chemical bond between two otherwise repelling ions, similar to what happens to two hydrogen atoms forming a hydrogen molecule. Two positronium hydride atoms (PsH) can form the stable species (PsH)2 when the two coupled positrons have opposite spins, while they form an antibonding state if they have the same spin. This is completely analogous to the landmark description by Heitler and London [Z. Phys. 44, 455 (1927)] on the formation of a chemical bond in the hydrogen molecule coupling two electrons with opposite spins. This is the first time two positrons are shown to behave like two electrons in ordinary matter, enlarging the definition of what is a chemical bond dating back to Lewis [J. Am. Chem. Soc. 38, 762 (1916)]. We suggest a few experimental routes to form and detect such a peculiar molecule. [ABSTRACT FROM AUTHOR]

We show that two positrons can form a chemical bond between two otherwise repelling ions, similar to what happens to two hydrogen atoms forming a hydrogen molecule. Two positronium hydride atoms (PsH) can form the stable species (PsH)2 when the two coupled positrons have opposite spins, while they form an antibonding state if they have the same spin. This is completely analogous to the landmark description by Heitler and London [Z. Phys. 44, 455 (1927)] on the formation of a chemical bond in the hydrogen molecule coupling two electrons with opposite spins. This is the first time two positrons are shown to behave like two electrons in ordinary matter, enlarging the definition of what is a chemical bond dating back to Lewis [J. Am. Chem. Soc. 38, 762 (1916)]. We suggest a few experimental routes to form and detect such a peculiar molecule. [ABSTRACT FROM AUTHOR]

The electron–positron oscillations (EPOs) around fixed massive ions in cold electron–positron–ion (EPI) plasmas mix up in phase and break at arbitrarily small amplitudes (C Maity, Phys. Plasmas21, 072317 (2014)). In the present paper, we report the collisional effects on the process of phase mixing of EPOs in such plasmas. For our purpose, we assume that the electrons and positrons suffer collisions with the static ions. A perturbation treatment of the basic equations is carried out to derive an expression for phase-mixing time. The phase-mixing time depends on the equilibrium ion to electron density ratio, the perturbation amplitude and the rate of collisions. The collisional effects are found to delay the overall phase mixing process of EPOs. [ABSTRACT FROM AUTHOR]

The propagation dynamics of the nucleus-acoustic waves (NAW) in a quantum plasma composed of nondegenerate inertial light nuclei, stationary heavy nuclei, and ultra-relativistically degenerate electrons and positrons has been theoretically investigated within the framework of the Boussinesq equation, which is valid for a bi-directional propagation of a small but finite amplitude limit. The N-soliton solution of the Boussinesq equation is derived using Hirota's method. It is found that positive potential structures exist in the sonic and supersonic regimes, whereas negative potential structures are found to be present in the subsonic regime. Pertinent plasma properties are analyzed for one-, two-, and three-soliton solutions in terms of different parameters. In addition to the typical solitary wave solutions, our findings indicate that the nonlinear NAW has breather structures. The three- and four-soliton solutions are used to construct the elastic interaction solutions of the breather–soliton and breather–breather, respectively. The findings are discussed in the context of ultra-relativistic astrophysical plasmas. [ABSTRACT FROM AUTHOR]

The article examines a mechanism that significantly influences the operation of radioelectronic equipment when it is located in close proximity to an electron accelerator. In particular, the effect of accumulation of an opposite sign charge and the appearance of micro-breakdown effects are considered in terms of this mechanism. A calculation model explaining these phenomena is described. The model is based on measuring the path of positrons and electrons in substances, as well as the characteristic dependence of the transmission coefficient for electrons and positrons on the path length. [ABSTRACT FROM AUTHOR]

Preserving the quality of a positron beam in a plasma-based accelerator, where a wakefield suitable for positron transport and acceleration is generated by means of an electron filament, is challenging. This is due to the nature of the wakefields, characterized by focusing fields that vary nonlinearly in the transverse direction, and by accelerating fields that are non-uniform. These fields also change slice-by-slice along the beam. Maintaining a high beam quality is pivotal for application of positron beams in a plasma-based collider. In this paper, we show that an initial background plasma temperature can help mitigate the positron beam quality degradation in plasma-based accelerators that rely on electron filaments. We show that temperature effects broaden the electron filament and smooth radially both the non-linear transverse and the non-uniform longitudinal wakefields. Using warm plasmas opens up new possibilities to improve beam quality in several plasma-based positron acceleration concepts. [ABSTRACT FROM AUTHOR]

Electron (e−) and positron (e+) bunch characteristics were directly measured for the first time by using wideband beam monitors (WBMs) and a detection system at the e+ source of the SuperKEKB B-factory. Secondarily generated e− and e+ bunches after the e+-production target were identified in their dynamical capture process at locations of the WBMs under a two-bunch acceleration scheme. The longitudinal and transverse bunch characteristics, the time intervals between the e− and e+ bunches, the bunch lengths, transverse bunch positions, and bunch charges were simultaneously separately measured for each bunch as functions of the capture phase to investigate their dynamical capture process. The results show that quite symmetric behaviors of the e− and e+ bunch characteristics were observed. The new WBMs open up a new window for direct measurements of both e− and e+ bunches during their dynamical capture process and in the optimization procedure of the e+ bunch intensity in multidimensional parameter spaces at any e+ sources. [ABSTRACT FROM AUTHOR]

Propagation of ion-acoustic compressive and rarefactive solitary waves has been studied in a magnetized collisional plasma comprising ions, positrons, dust grains, and kappa-distributed cold and hot electrons. The Damped Zakharsov–Kuznetsov–Burgers (DZKB) equation has been formed using the basic equation with the aid of the reductive perturbation method (RPM). Considering small dissipation exists in the plasma environment, a small amplitude solitary wave solution of the DZKB equation has been derived assuming the validity of conservation law in that nonlinear system. Amplitude and width of the solution strongly depend on the nonlinear and dispersion coefficients of the evolution equation, which are the functions of different plasma parameters, the kinematic viscosity, collisional frequency, ratio of the temperatures of cold and hot electrons, density ratio of cold electrons, concentration of positron particles and concentration of dust particles, and however a significant dependency of the solution on the Burgers and damping term is also found. On the other hand in many times, the dusty plasma becomes strongly dissipative, and naturally, conservation law fails in the system. In general, strong dissipation generates shock waves which becomes a further study through a new solution derived using the extended tanh method. Finally, the parametric studies of solitary solutions are described from a numerical standpoint. [ABSTRACT FROM AUTHOR]

Laser–plasma accelerators (LPAs) have been demonstrated as one of the candidates for traditional accelerators and have attracted increasing attention due to their compact size, high acceleration gradients, low cost, etc. However, LPAs for positrons still face many challenges, such as the beam divergence controlling, large energy spread, and complicated plasma backgrounds. Here, we propose a possible multistage positron acceleration scheme for high energy positron beam acceleration and propagation. It is driven by the strong coherent THz radiation generated when an injected electron ring beam passes through one or more solid targets. Multidimensional particle-in-cell simulations demonstrated that each acceleration stage is able to provide nearly 200 MeV energy gain for the positrons. Meanwhile, the positron beam energy spread can be controlled within 2%, and the beam emittance can be maintained during the beam acceleration and propagation. This may attract one's interests in potential experiments on both large laser facilities and a traditional accelerator together with a laser system. [ABSTRACT FROM AUTHOR]

The positron annihilation lifetimes were measured using a 48 V positron source in noncentrosymmetric cubic single crystals of CoSi, FeSi and MnSi. The following lifetimes were determined from the positron annihilation time spectra: 168(1) ps for CoSi, 114(1) ps for FeSi and 111(1) ps for MnSi. For single-crystal CoSi, the positron annihilation lifetime was also determined with a 22 Na positron source. For CoSi, the lifetimes obtained from different positron sources are consistent. The differences in the positron annihilation lifetimes in MnSi and FeSi, on the one hand, and in the Weyl semimetal CoSi, on the other hand, are possibly caused by the formation of a positron + electron bound state (positronium). [ABSTRACT FROM AUTHOR]

The positron impact cross-sections of pyrimidine molecules are reported from 1 eV to 5000 eV. These cross-sections include differential elastic, integral elastic, and direct ionisation. The elastic cross-sections are computed using the single-centre expansion scheme whereas the direct ionisation cross-sections are obtained using the binary-encounter-Bethe formula. The integral and differential cross-sections exhibit consistency with the experimental and other theoretical results. The direct ionisation cross-sections, which are reported for the first time, are compared with the experimental inelastic cross-sections (the sum of excitation and ionisation) to assess the trends in theoretically computed ionisation cross-sections and with the corresponding results for the electrons. The incoherently summed elastic and ionisation cross-sections match very well with the total cross-sections after 40 eV indicating the minimal impact of the positronium formation and electronic excitation processes. Based on this study, we recommend that the experimental data of the inelastic cross-sections reported by Palihawadana et al. be revisited. [ABSTRACT FROM AUTHOR]

We present theoretical studies of electron and positron interaction with protons aligned in a one-dimension periodic line. The equally spaced protons were artificially generated where the individual protons are fixed in a certain position. The incident energies were 500 eV and 1000 eV. The electron and positron trajectories passing through these periodic multiple scattering objects were calculated using a classical trajectory Monte Carlo method. We show that this proton configuration has focusing and defocusing properties depending on the certain initial conditions. [ABSTRACT FROM AUTHOR]

Radiation damage is a key challenge for materials. Accurate evaluation of radiation damage is a starting point for investigating the behaviors of materials used in a radiation environment. The present work proposes improved methods for calculating the primary radiation damage cross sections induced by light particles, including electrons, positrons, and photons. The main improvements compared with previous methods are: (1) accurate Mott cross section rather than the McKinley-Feshbach analytical approach is used for electron and positron scattering; (2) data and methods recommended by the International Commission on Radiation Unit and measurements (ICRU) are systematically applied for computing the stopping powers of electron and positron; (3) accurate differential cross section by combining different models instead of some simple approaches is used for pair production. The electron, positron, and photon irradiation-induced displacement cross sections for various important elements covering a large range of atomic numbers (from Li to U) are computed with the improved methods for energy up to 100 MeV. The calculated displacement cross sections are also tabulated so that they can be simply used for further applications. [ABSTRACT FROM AUTHOR]

The head-on collision between two-counter-propagating electron acoustic solitons and double layers (DLs) in an unmagnetized collisionless multi-species plasma consisting of inertial cold electron fluid and (α, q)-distributed hot electrons and positrons has been analyzed with the stationary background of massive positive ions. For nonlinear analysis of colliding wave phenomena, the coupled Korteweg–de Vries equation (KdVE), modified KdVE (mKdVE), and standard Gardner equation have been derived by adopting the extended Poincaré–Lighthill–Kuo technique. The effect of non-dimensional parameters on the collisional KdV, mKdV, and Gardner solitons (GSs) and DLs has been examined in detail by considering the limiting cases of (α, q)-distributions. It is found that the plasma model supports (i) the compressive and rarefactive collisional KdV solitons and GSs, (ii) only compressive mKdV solitons, and (iii) only rarefactive collisional DLs. The rarefactive collisional solitons are more affected by nonextensivity and the increase of the temperature of electrons than their compressive counterpart, whereas the rarefactive collisional DLs only existed in the presence of nonthermality. [ABSTRACT FROM AUTHOR]

The nonlinear characteristics of Alfvén waves in a plasma medium composed of double spectral electron distribution and positive and negative ions are investigated. A Korteweg–de Vries (KdV-type) equation is derived using the reductive perturbation technique. The periodic and soliton structures are investigated. The effects of the two spectral indices r and q on the produced periodic structures are studied. It is found that the amplitude of the rarefactive periodic wave increases by increasing the values of r and q. Some external perturbation intruders on the system are considered, and the quasi periodic and chaotic structures of Alfvén waves are discussed. It is found that by decreasing the values of β − (knowing that β known as the ratio of kinetic to magnetic pressures), the periodic structure is converted gradually into chaotic structure passing through the quasi-periodic one. The results of this study are helpful in describing the behavior of the Alfvénic structure of periodic waves and other related events in the ionosphere region. [ABSTRACT FROM AUTHOR]

Cosmic ray fluxes in the heliosphere are modulated by solar wind with an embedded solar interplanetary magnetic field. The solar activity changes with a period of ~11 year, and this is the main reason for the observed 11-year variations of cosmic ray fluxes. Besides this, the directions of magnetic fields in solar polar regions and in the heliosphere change to the opposite direction every ~11-years. This causes, in addition, the presence of another 22-year solar magnetic cycle and contributes features to the known ~11-cycle. In this article, we discuss the generally accepted picture of cosmic ray modulation in the heliosphere and show that it requires several changes. [ABSTRACT FROM AUTHOR]

We explore the signals of axion-like particles (ALPs) via the process e + e âˆ' â†' aÎł â†' 3 Îł at the Circular Electron Positron Collider (CEPC). The expected sensitivities of the CEPC with the center of mass energy s = 240 GeV for the ALP parameter space are obtained. Our results show that the promising sensitivities of the CEPC to the coupling g aγγ are in the range of 3.25 Ă— 10âˆ'5 GeVâˆ'1 to 3.7 Ă— 10âˆ'4 GeVâˆ'1 with the ALP mass m a from 2.9 GeV to 190 GeV. [ABSTRACT FROM AUTHOR]

• In the Galaxy active dwarf stars are the sources of cosmic rays. • These particles are produced in stellar flares. • The power of these stellar flares is enough to provide the density of energy of galactic cosmic rays observed in Galaxy. • In stellar flares positrons are also produced. • This production explains the positron excess recorded in space experiments. There are approximately (2–4)·1011 stars in the Galaxy. Many of these stars produce stellar flares, that is, they are active stars. It is known that our Sun accelerates charged particles during powerful solar flares. If solar and stellar flares are compared, one can find many common features in these phenomena, and it is generally assumed that the underlying mechanism in solar and stellar flares is the same. To explain the experimental data on cosmic rays obtained recently using balloons and space experiments, the existence of cosmic ray sources near the solar system is required. In the present article, we discuss briefly some cosmic ray experimental data that can be explained if sources of cosmic rays exist near the solar system. We consider active dwarf stars as cosmic ray sources (in addition to supernova remnants). These stars constitute the main stellar population in the Galaxy and generate powerful stellar flares, which are much more powerful than solar ones (up to 107 times). This suggestion enables to understand many features observed in cosmic rays over the past 20 years. In particular, the explanation of the positron excess is given in the frame of the known mechanisms without attracting dark matter. [ABSTRACT FROM AUTHOR]

The CEPC Plasma Injector is designed as the beam energy multiplier for avoiding the dipole magnet issue of the Circular Electron Positron Collider (CEPC) booster. Besides the final energy, other requirements including the energy stability, bunch charge and energy spread all make the injector design very challenging. With respect to the electron acceleration, a high transformer ratio plasma wakefield acceleration stage is necessary if we constrain the beam energy at the end of the linac and the plasma injector are 10 GeV and 45.5 GeV, respectively. In this work, we use the particle-in-cell code QuickPIC to design the electron acceleration stage. Based on the current conceptual design, a comprehensive analysis of single-parameter tolerance is performed. Through the tolerance studies, we obtain some useful guidance for the further optimization of the injector. [ABSTRACT FROM AUTHOR]

The pulses collision scheme has been demonstrated to be an effective way for the Breit–Wheeler positron generation. In this work, positron generation via two circularly polarized laser pulses colliding in near-critical-density plasmas with different thicknesses is further studied. The results show that high flux and high density positrons are generated and collected in 14 μm thick plasmas as extra backflow electrons contribute to radiation. Though the positron yield in 4 μm thick plasmas is lower than that in the thick plasmas, partial positrons are accelerated out of the collision region with a small divergence and quasi-monoenergetic energy. It is found that the Lorentz field dominates positron acceleration and collection. This investigation will further facilitate quality positron generation and application. [ABSTRACT FROM AUTHOR]

The BESIII experiment at the Beijing Electron Positron Collider (BEPCII) collected large data samples for electron-positron collisions with center-of-mass from 3.773 to 4.700 GeV. The analysis of these samples has resulted in a number of surprising discoveries, such as the discoveries of the electrically charged Z cs (3895) ± structures, which is assumed to be an exotic tetraquark and contains a strange quark. In this talk, we will review the current status of the analysis of the exotic charmonium-like states at BESIII. [ABSTRACT FROM AUTHOR]

The excitation cross-sections of the nS states of atomic hydrogen, n = 2 to 6, by electron impact on the ground state of atomic hydrogen were calculated using the variational polarized-orbital method at various incident electron energies in the range 10 to 122 eV. Converged excitation cross-sections were obtained using sixteen partial waves (L = 0 to 15). Excitation cross-sections to 2S state, calculated earlier, were calculated at higher energies than before. Results obtained using the hybrid theory (variational polarized orbital method) are compared to those obtained using other approaches such as the Born–Oppenheimer, close-coupling, R-matrix, and complex-exterior scaling methods using only the spherical symmetric wave functions. Phase shifts and elastic cross-sections are given at various energies and angular momenta. Excitation rate coefficients were calculated at various electron temperatures, which are required for plasma diagnostics in solar and astrophysics to infer plasma parameters. Excitation cross-sections are compared with those obtained by positron impact excitation. [ABSTRACT FROM AUTHOR]

Focusing on the electron and positron spectrum measured with the Calorimetric Electron Telescope (CALET), which shows characteristic structures, we calculate the flux contributions of cosmic rays that have escaped from randomly appearing supernova remnants. We adopt a Monte Carlo method to take into account the stochastic nature of the appearance of nearby sources. We find that without a complicated energy dependence of the diffusion coefficient, simple power-law diffusion coefficients can produce spectra similar to the CALET spectrum, even with a dispersion in the injection index. The positron component measured with AMS-02 is consistent with a bump-like structure around 300 GeV in the CALET spectrum. One to three nearby supernovae can contribute up to a few tens of percent of the CALET flux at 2â€"4 TeV, while ten or more unknown and distant (≳500 pc) supernovae account for the remaining several tens of percent of the flux. The CALET spectrum, showing a sharp drop at ∼1 TeV, allows for a contribution of cosmic rays from an extraordinary event that occurred ∼400 kyr ago. This type of event releases electrons/positrons with a total energy more than 10 times the average energy for usual supernovae, and its occurrence rate is lower than one three-hundredth of the usual supernova rate. [ABSTRACT FROM AUTHOR]

We describe the production of a high-resolution electron beam using a Penning–Malmberg buffer-gas trap, or Surko trap as they have become known. A high-flux beam with an energy width of ~ 30 meV (FWHM) is readily achieved and the efficiency of production is considerably higher than that for positrons in a similar trap configuration. The reasons for this become apparent when one considers the molecular collisions and the respective selection rules involved, for electrons and positrons. We demonstrate the production of the beam and the capacity that it realises for absolute scattering measurements and for high-resolution electron spectroscopy. [ABSTRACT FROM AUTHOR]

Based on the fact that the electromagnetic potential can interact with charged particle and using the Dirac field of conjugated mass and energy introduced in a previous paper, we show, in the framework of quantum field theory (QFT), that it would be possible experimentally to highlight significant differences in the probabilities of occurrence of electron and positron states depending on whether electrons and positrons states of conjugated mass and energy exist or not. [ABSTRACT FROM AUTHOR]

The positron–electron fluxes detected by AMS02, CALET, DAMPE and Fermi-LAT have shown their complex structure which deviated from a single power-law, and the results of DAMPE and Fermi-LAT are obviously higher than those of AMS02 and CALET in 100 GeV–1 TeV range. We point out that the complex positron–electron flux structures can be attributed to two sources with a natural background, and the difference between the two groups of data can be explained in an anomalous bremsstrahlung theory. [ABSTRACT FROM AUTHOR]

Diffuse radio emission at the centre of galaxy clusters has been observed both in merging clusters on scales of Mpc, called giant radio haloes, and in relaxed systems with a cool-core on smaller scales, named mini haloes. Giant radio haloes and mini haloes are thought to be distinct classes of sources. However, recent observations have revealed the presence of diffuse radio emission on Mpc scales in clusters that do not show strong dynamical activity. RX J1720.1+2638 is a cool-core cluster, presenting both a bright central mini halo and a fainter diffuse, steep-spectrum emission extending beyond the cluster core that resembles giant radio halo emission. In this paper, we present new observations performed with the LOw Frequency ARray Low Band Antennas (LBA) at 54 MHz. These observations, combined with data at higher frequencies, allow us to constrain the spectral properties of the radio emission. The large-scale emission presents an ultrasteep spectrum with |$\alpha _{54}^{144}\sim 3.2$|⁠. The radio emission inside and outside the cluster core have strictly different properties, as there is a net change in spectral index and they follow different radio-X-ray surface brightness correlations. We argue that the large-scale diffuse emission is generated by particles re-acceleration after a minor merger. While for the central mini halo, we suggest that it could be generated by secondary electrons and positrons from hadronic interactions of relativistic nuclei with the dense cool-core gas, as an alternative to re-acceleration models. [ABSTRACT FROM AUTHOR]

This study seeks to calculate the conversion coefficients from fluence to local skin absorbed dose for monoenergetic electrons and positrons from 0.01 to 10 MeV. The conversion coefficients calculation used a new analytical approach. The obtained results are in good agreement with those previous published. A new analytical fit has provided a convenient approach for determining conversion coefficients for discrete incidents. [ABSTRACT FROM AUTHOR]

Preliminary experiments have been performed toward the development of a multi-cell Penning–Malmberg trap for the storage of large numbers of positrons (≥1010e+). We introduce the master-cell test trap and the diagnostic tools for first experiments with electrons. The usage of a phosphor screen to measure the z-integrated plasma distribution and the number of confined particles is demonstrated, as well as the trap alignment to the magnetic field (B = 3.1 T) using the m = 1 diocotron mode. The plasma parameters and expansion are described along with the autoresonant excitation of the diocotron mode using rotating dipole fields and frequency chirped sinusoidal drive signals. We analyze the reproducibility of the excitation and use these findings to settle on the path for the next generation multi-cell test device. [ABSTRACT FROM AUTHOR]

Mu3e is a dedicated experiment designed to find or exclude the charged lepton flavor violating µ eee decay at branching fractions above 10-16. The search is pursued in two operational phases: Phase I uses an existing beamline at the Paul Scherrer Institute (PSI), targeting a single event sensitivity of 2 • 10-15, while the ultimate sensitivity is reached in Phase II using a high intensity muon beamline under study at PSI. As the µ → eee decay is heavily suppressed in the Standard Model of particle physics, the observation of such a signal would be an unambiguous indication of the existence of new physics. Achieving the desired sensitivity requires a high rate of muons (108 stopped muons per second) along with a detector with large kinematic acceptance and efficiency, able to reconstruct the low momentum of the decay electrons and positrons. To achieve this goal, the Mu3e experiment is mounted with an ultra thin tracking detector based on monolithic active pixel sensors for excellent momentum and vertex resolution, combined with scintillating fibers and tiles for precise timing measurements. [ABSTRACT FROM AUTHOR]

Very local interstellar spectra (vLIS's) for protons and total Helium (He) were observed in situ by Voyager 1 below about 340 MeV/ since it had moved across the heliopause (HP). Together with high precision PAMELA and AMS observations at the Earth, we previously reported on new vLIS calculated from 1 MeV to 100 GeV for protons, electrons, total He, Oxygen, Carbon, and Boron. We now follow this up to report on the vLIS's for positrons and for the isotopes He-3, He-4, and Deuteron (H-2) by combining computations with the galactic propagation code, GALPROP, and our 3D modulation model for GCRs in the heliosphere as done previously. Similarly, we also have computed updates of the vLIS's for antiprotons and antideuteron. We assume that the modulation processes between the HP and the Earth for protons and other GCR nuclei are essentially similar, which is also the case for electrons and positrons, except for particle drifts of oppositely charged particles. The procedures followed to obtain these updates are summarized and a compilation of the mentioned vLIS's is presented. [ABSTRACT FROM AUTHOR]

Slow and fast modulation instability and envelope soliton of ion-acoustic wave (IAW) are studied in an electron–ion–positron plasma when the ions are warm and have constant stream velocity, positrons are isothermal and electrons are superthermal. The non-linear Schrodinger (NLS) equation has been derived using the Fried and Ichikawa method and the solution of envelope soliton is obtained. It is seen that IAW propagates with two modes (slow and fast) in the presence of an ion stream in the plasma which results in slow and fast modulation instability of the wave. The stability criteria for slow mode (SM) and fast mode (FM) of the wave are established and studied graphically for different values of the ion temperature, positron density, positron temperature and kappa factor of electrons. The bright envelope soliton and dark envelope soliton of SM and FMs of the wave in electron–ion–positron plasma are also studied. The solution of rogue waves (RWs) is obtained from the NLS equation and the nature of RWs of the SM and FM of the wave is discussed graphically. Our results are new and no author has reported this kind of results of slow and fast modulation instability of IAW till now. [ABSTRACT FROM AUTHOR]