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The electromagnetic form factors of the proton and the neutron in the timelike region are investigated. Electron–positron annihilation into antinucleon-nucleon ( N ¯ N) pairs is treated in distorted wave Born approximation, including the final-state interaction in the N ¯ N system. The latter is obtained by a Lippmann–Schwinger equation for N ¯ N potentials derived within SU(3) chiral effective field theory. By fitting to the phase shifts and (differential) cross section data, a high quality description is achieved. With these amplitudes, the oscillations of the electromagnetic form factors of the proton and the neutron are studied. It is found that each of them can be described by two fractional oscillators. One is characterized as "overdamped" and dominates near the threshold, while the other is "underdamped" and plays an important role in the high-energy region. These two oscillators are essential to understand the distributions of polarized electric charges induced by hard photons for the nucleons. [ABSTRACT FROM AUTHOR]

Magnetic bottle Time-of-Flight (ToF) spectrometers can measure the energy spectra of all electrons emitted into a 2π sr solid angle simultaneously, greatly reducing data collection time. When the detection of the annihilation gamma (γ) and the detection of the electron (e) are used as timing signals for ToF spectrometers, the e-γ time difference spectra (e-γ TDS) are reflective of the positron-induced electron energy distributions provided the times between the impact of the positrons and the emission of the annihilation gammas are short compared to the flight times of the electrons. This is typically the case since positrons have short lifetime in solids (∼100–500 ps) compared to the flight times of the secondary electrons (102 ns to 103 ns). However, if the positron leaves the surface as a positronium atom (a bound electron–positron state), the annihilation gamma photons can be appreciably delayed due to the longer ortho -positronium (o-Ps) lifetime. This can result in an e-γ TDS having an exponential tail with a decay constant related to the o-Ps lifetime. Here, we present an analysis of the e-γ TDS using a Monte Carlo model which estimates the spectral contributions resulting from o-Ps annihilations. By removing the contributions from the delayed gamma signal, the energy spectrum of Positron Impact-Induced Secondary electrons (PIISE) can be isolated. Furthermore, our analysis allows an estimation of the intensity of the exponential tail in the e-γ TDS providing a method to measure the fraction of positrons that form Ps at solid surfaces without relying on assumed 100 % Ps emitting surfaces for calibration. [ABSTRACT FROM AUTHOR]

The feasibility of gamma-ray light sources based on the channeling phenomenon of ultrarelativistic electrons and positrons in oriented crystals that are periodically bent with Small Amplitude and Short Period (SASP) is demonstrated by means of rigorous numerical modeling that accounts for the interaction of a projectile with all atoms of the crystalline environment. Numerical data on the spectral distribution, brilliance, number of photons and power of radiation emitted by 10 GeV electron and positron beams passing through diamond, silicon and germanium crystals are presented and analyzed. The case studies presented in the paper refer to the FACET-II beams available at the SLAC facility. It is shown that the SASP bending gives rise to the radiation enhancement in the GeV photon energy range where the peak brilliance of radiation can be as high as on the 1 0 24 photons/s/mrad 2 /mm 2 /0.1% BW. The parameters of radiation can be tuned by varying the amplitude and period of bending. [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]

Investigating the mechanism of positron annihilation in liquid-scintillator based neutrino experiments could be helpful for positron reconstruction algorithms and positron-electron discrimination analysis. Based on this, we utilize a novel positron annihilation lifetime spectrometer to characterize a series of liquid scintillator samples without direct contact with the positron source by applying the anti-coincidence method, which facilitates the measurement of liquids with high accuracy and low background. We obtain an ortho-positronium (o-Ps) lifetime value of 3.02 ns for liquid scintillators composed of linear alkylbenzene and two solutes, and we also measure liquid scintillator samples by bubbling different gases to study the interaction of oxygen dissolved with positronium. The discussion of the annihilation behavior of o-Ps in liquid scintillators further clarify the factors affecting the lifetime and intensity of o-Ps, and the calculation of annihilation rate and free volume radius within the samples has potential applications in characterizing gas solubility and free volume in liquids with o-Ps as probe. • The o-Ps properties in liquid scintillator are investigated by a novel PALS device with anti-coincidence method. • The higher oxygen solubility in liquid scintillator compared to water significantly affects the lifetime of o-Ps. • Dissolved oxygen concentration in liquid scintillators shortens o-Ps lifetimes as it increases. • As a free-volume probe, o-Ps can characterize the nanostructure and gas solubility of molecular liquids. [ABSTRACT FROM AUTHOR]

This study investigates the influence of CoO doping on concentration and characteristics of nano-sized cavities in Li₂SO₄-MgO-P₂O₅ glasses using positron annihilation lifetime spectroscopy (PALS). These defects are known to significantly impact the physical properties of glasses. Glasses with compositions of 20 Li₂SO₄-20MgO-(60- x) P₂O₅: x CoO (0 ≤ x ≤ 1.0 mol%), were prepared using melt-quench technique. PALS analysis revealed a strong dependence of positronium (e⁺- e⁻ pair) lifetime on CoO concentration. The analysis of the results further indicated that the fraction of free volume Δ f/f 0) and cavity radius (R) reached minimum values between 0.6 and 0.8 mol% CoO, but increased with further CoO doping. This suggests that cobalt ions prefer O h sites, act as network modifiers, and create a larger concentration of free volume defects when CoO is increased beyond 0.8 mol%. Notably, the PALS-derived free volume defect concentration with CoO concentration is found to follow nearly same trend exhibited by the results of optical absorption and AC conductivity studies. [ABSTRACT FROM AUTHOR]

State-selective total and angular differential cross sections for positronium formation are presented in the collision of positron with helium atoms in their ground state by using the four-body formalism of the boundary-corrected continuum-intermediate-states approximation. The main purpose of the present study is to investigate the relative importance of intermediate ionization continuum states that has been incorporated with a suitable choice of distorting potential. In addition, the nine-dimensional integrals of the transition amplitude are analytically reduced to a one-dimensional real integral, which can be easily calculated numerically. The influence of the target static electron correlations on the capture probability is investigated using the different bound-state wave functions of He. The theoretical model for the calculation is fairly accurate and predicts a number of interesting features of the state-selective total and differential cross sections in the range of positron impact energy varies from 20 to 250 eV. The total cross sections are highly peaked at an impact energy of 50 eV. The results are compared with those of other theories and the available experimental data. The present theoretical results and other measurements show satisfactory agreement in the wide energy range. Moreover, surface plots for the state-selective differential cross sections are also presented to illustrate the interesting feature of the positronium formation in this collision process. • Boundary-corrected continuum-intermediate-state approximation is used to study the positronium formation in positron–helium collision. • Purpose of the present study is to investigate the relative importance of the intermediate ionization continuum states and the correlated wavefunction for the helium atom in ground state. • The probability of positronium formation is maximum near about 50 eV positron impact energy. • Angular differential cross section shows a dip where the probability of positronium production is minimum. Such dip shifts towards the smaller scattering angles with increasing impact energy. [ABSTRACT FROM AUTHOR]

Positron annihilation age–momentum correlation (AMOC) spectroscopy is not only a critical approach to investigate positronium formation and annihilation, but also a powerful technique for materials science to characterize the chemical environment of pores. However, due to the long measurement time (several days to collect 10 million counts for one sample, at a low coincidence counting rate of approximately 20–40 cps) of a conventional non-beam-based AMOC spectrometer, AMOC technique has been rarely applied. In this work, based on the geometrical simulations of detectors using Geant4 program, we developed a new semi-digital AMOC spectrometer with two start detectors. After systematic optimizations of geometrical configurations of detectors, timebase of digital oscilloscope, and the energy windows of start and stop detectors, this instrument achieved the highest coincidence counting rate for a non-beam-based AMOC spectrometer (∼ 180 cps for a narrow stop energy window of 469–589 keV and the shaping time of HPGe detector at T HPGe shaping = 6 μ s , and ∼ 500 cps for a wide stop energy window of 104–589 keV and T HPGe shaping = 2 μ s). The drastic rise of coincidence counting rate will broaden the applications of AMOC spectrometers in positronium physics and materials characterization in future. • Simulations and experiments of the geometrical optimization of AMOC system were performed. • A method was proposed to merge PAL spectra with different channel widths. • Various basetime configurations that affect the counting rate of AMOC system were discussed. • The effects of energy windows of start and stop detectors on the counting rate of AMOC system were studied. • The highest coincidence counting rate was achieved for a non-beam-based AMOC spectrometer. [ABSTRACT FROM AUTHOR]

Positronium (Ps) is an exotic hydrogenic atom composed of an electron bound to a positron via the Coulomb force. Being composed of two low-mass leptons, positronium is, for all practical purposes, fully described by quantum electrodynamics (QED). The absence of hadronic components suggests that positronium energy levels and decay rates can be calculated to very high precision, limited only by the order of the corresponding perturbative expansion and the tiny effects of heavy or weakly interacting virtual particles and exotic decay modes. Moreover, as it is a low-mass particle–antiparticle system, the QED description of positronium is strongly affected by annihilation and recoil effects that are either weaker or not present in other atoms. As a result, sufficiently precise measurements of Ps energy levels and decay properties can serve as stringent tests of bound-state QED theory, and may be sensitive to processes not present in the theory, such as axion-like particles (beyond the QCD axion), or a fifth fundamental force. In addition, since positronium is an eigenstate of the fundamental symmetries C and P, various symmetry violating mechanisms can be probed through searches for anomalous decay modes. In the last three decades, there have been significant experimental advances in positron and positronium physics which open up the possibility to test QED bound-state theory with unprecedented precision. Here we present the current state-of-the-art in experimental positronium spectroscopy, and discuss explicitly how such measurements can be used to test bound-state QED theory, and how such tests may contribute to the search for physics beyond the Standard Model. [ABSTRACT FROM AUTHOR]

Proton-conducting polymers play a pivotal role in clean energy technologies and various industrial applications, with a significant emphasis on enhancing energy efficiency and minimizing environmental impact. Sulfonated polyether ether ketone (SPEEK), which is renowned for its proton conductivity, has emerged as a key material in electrochemical processes, notably in proton exchange membrane (PEM) fuel cells. This study investigated the proton conductivity and dielectric behavior of SPEEK electrolytes at varying degree of sulfonation (DS) of 65% and 80%, correlating these properties with free volume profiles determined by positron annihilation lifetime spectroscopy (PALS). The SPEEK-65 and SPEEK-80 electrolytes were prepared via a controlled sulfonation process and characterized by FTIR, TGA, and SEM analyses. Proton conductivity and dielectric measurements were conducted at temperatures ranging from 300 to 370 K and frequencies ranging from 20 Hz to 1 MHz. The results revealed that SPEEK-80 exhibited a maximum proton conductivity of 3.4 × 10−2 S/m at 300 K and 1 MHz, which was significantly greater than the 4.38 × 10−3 S/m observed for SPEEK-65 under the same conditions. PALS analysis demonstrated a notable increase in free volume with increasing DS, with SPEEK-80 showing a higher o-Ps lifetime and intensity, indicating larger free volume sizes and fractions. These findings underscore the critical interplay between DS, free volume, and proton conductivity, offering insights into optimizing SPEEK-based electrolytes for advanced electrochemical applications. • Positron lifetime correlated with conductivity via free volume determination. • PALS revealed higher DS in SPEEK-80 increased free volume and o-Ps lifetimes. • Proton conductivity in SPEEK-80 rose with DS, enhancing proton transport. • Dielectric behavior in SPEEK reflects DS influence on dipole alignment. • Frequency-dependent dielectric changes reveal DS impact on SPEEK's polarization. [ABSTRACT FROM AUTHOR]

Positronium (Ps) imaging has been recently spotlighted for its potential applications in nuclear medicine. Among them, we expect that the Ps lifetime can be a sensor for tumor hypoxia; hence, we are aiming to achieve Ps lifetime imaging, Quantum PET (Q-PET), based on whole gamma imaging (WGI). A linear correlation was previously shown between the Ps lifetime and the oxygen partial pressure (pO 2) in water by using a bench-top detector system. However, nobody has ever measured the Ps lifetimes for pO 2 values of 10 mmHg and 40 mmHg, corresponding to hypoxic cancer cells and healthy tissue cells, respectively. Therefore, this study aimed at measuring the Ps lifetime of 22Na solutions each having such tiny differences in the pO 2 value. For possible extension toward imaging, we used VRAIN, a clinical brain-dedicated time-of-flight (TOF) PET system. The pO 2 values of the 22Na solutions were adjusted to 0, 10, 40, and 160 (air) mmHg by adjusting the inflow of nitrogen gas. Each 22Na solution was placed near the center of the detector geometry and measured. Three different energy windows (EWs) for 1275 keV gamma detection were compared (1100–1500 keV, 900–1500 keV and 700–1500 keV). Due to the increased number of events, the error values (σ: standard deviation) of the calculated Ps lifetimes decreased as the EW widened. The optimized EW was determined to be 700–1500 keV, which showed the lowest error value. The Ps lifetime values gradually became shorter as the pO 2 values increased. The Ps lifetime values at 0 mmHg and 160 mmHg were 1.9389 ± 0.0025 ns and 1.9104 ± 0.0024 ns at the EW of 700–1500 keV. The difference between the lifetime values was more than three times the errors (±3σ), and we considered it was a statistically significant difference. The Ps lifetime values of 10 mmHg and 40 mmHg were 1.9360 ± 0.0026 ns and 1.9291 ± 0.0024 ns at the same condition, and the difference could be distinguished with an error value of more than ± 1σ. [ABSTRACT FROM AUTHOR]

In this work we report on the systematic characterization of a rare-gas moderated magnetically-transported continuous positron beam based on a 22Na radioactive source. The characterization was performed with three different rare-gas solid moderators: Ne, Ar, and Kr. Each moderator was deposited and then thermal annealed at temperature ∼ 35 % and ∼ 30 % lower than the melting point, respectively. Tests of moderation/magnetic transport efficiency of the apparatus have shown a maximum efficiency of 1.8 10-3, 2.0 10-3 and 0.6 10-3 for Ne, Ar, and Kr, respectively. The average longitudinal kinetic energy of positrons was found to be ∼ 0.95 eV, ∼1.25 eV, and ∼ 0.45 eV for Ne, Ar, and Kr moderator, respectively. The spin polarization measurement of moderated positrons was performed by using the Doppler broadening of the annihilation γ-rays from positronium formed in oxidized nanochanneled silicon positron/positronium converters. Polarization values of 0.30 ± 0.01, 0.29 ± 0.01 and 0.29 ± 0.01 were found for Ne, Ar, and Kr moderator, respectively. [ABSTRACT FROM AUTHOR]

Silicon nanochannel plates (NCPs) are efficient positron to positronium converters and are employed as sources of abundant cold positronium. Characterization of the emitted positronium energy spectrum is crucial to assess the NCP performance and support their further optimization. We present here a Time-of-Flight (ToF) system optimized to measure the energy spectrum of positronium produced by NCP converters held at cryogenic temperatures. The ToF-apparatus was tested by implanting 7 keV positrons into NCPs at room temperature before performing ToF experiments using positron implantation energies of 7 and 11 keV into NCPs held at 20 K. At these conditions we succeeded in determining the energy spectrum of the positronium escaping from the nanochannels into the vacuum down to an energy of 10 meV. [ABSTRACT FROM AUTHOR]

Studies based on imaging the annihilation of the electron (e −) and its antiparticle positron (e +) open up several interesting applications in nuclear medicine and fundamental research. The annihilation process involves both the direct conversion of e + e − into photons and the formation of their atomically bound state, the positronium atom (Ps), which can be used as a probe for fundamental studies. With the ability to produce large quantities of Ps, manipulate them in a long-lived Ps states, and image their annihilations after a free fall or after passing through atomic interferometers, this purely leptonic antimatter system can be used to perform inertial sensing studies in view of a direct test of Einstein's equivalence principle. It is envisioned that modular multi-strip detectors can be exploited as potential detection units for this kind of studies. In this work, we report the results of the first feasibility study performed on a e + beamline using two detection modules to evaluate their reconstruction performance and spatial resolution for imaging e + e − annihilations and thus their applicability for gravitational studies of Ps. [ABSTRACT FROM AUTHOR]

A technique for measuring high-energy electrons using Si detectors of various thicknesses that are much smaller than the range of the examined electrons is presented. The advantages of the method are discussed on the basis of electron–positron pair creation recently studied in deuteron–deuteron fusion reactions at very low energies. Careful Geant4 Monte Carlo simulations enabled to identify the main spectral contributions of emitted electrons and positrons resulting from the energy loss mechanisms and scattering processes within the target, detector and their holders. Significant changes in the intensity of the detected electrons, depending on the detector thickness and the thicknesses of absorption foils placed in the front of the detector could be observed. The corresponding correction factors have been calculated and can be used for different applications in basic and applied research. • Highly efficient measurement of high-energy electrons using thin Si detectors. • The method is applicable for weak nuclear process studies in close geometries. • Geant4 simulations enable to recognize the different electron spectral contributions. • Strength of the absorption peak depends on detector and absorption foil thicknesses. • Internal e+e- pair creation could be observed in the deuteron–deuteron reaction. [ABSTRACT FROM AUTHOR]

The annihilation sites of ortho-positronium formed by positrons incident on Y zeolites with different Si/Al ratios are investigated by positron annihilation lifetime spectroscopy in different environments. Comparison of the measured ortho-positronium lifetimes by exposure of the zeolites to argon, nitrogen, water or vacuum enables us to determine the annihilation process and the specific annihilation site within the zeolite samples. The third lifetime component is ascribed to ortho-positronium pick-off annihilation in or around the apertures of the sodalite cage and in the connecting channels, and is reduced in water because of the physisorbed molecules that hinder the ortho-positronium mobility. The longest fourth lifetime component is attributed to ortho-positronium self-annihilation in the interparticle gaps, but is significantly suppressed in the presence of polar molecules, which suggests a contribution from ortho-positronium pick-off annihilation in the supercage. • Ortho-positronium annihilation modes and sites in Y zeolites are determined. • Positronium lifetimes vary drastically by exposure to different environments. • Long-lived component arises from multiple positronium annihilation processes. • Water physisorption promotes pick-off annihilation and inhibits self-annihilation. [ABSTRACT FROM AUTHOR]

We present triple-differential cross section results for the positron and electron induced single ionization of the Ar (3p) and Ar (3s) atoms at incident energy 1 keV. The triple-differential cross sections (TDCSs) have been calculated in the modified distorted wave formalism using the second Born approximation. The TDCSs have been calculated in coplanar asymmetric geometry for different kinematical conditions. The second Born term has been found to be significant in obtaining the TDCS for electron as well as positron impact at smaller values of momentum transfer and it produces better agreement with the recent available measurements for Ar (3p). With the increase of momentum transfer, the dominance of binary emission of electrons has been found to increase for the positron impact ionization of Ar (3s). [ABSTRACT FROM AUTHOR]

• Eelectromagnetic solitary waves can propagate as compressive or rarefactive type solitons. • The electromagnetic solitons exist symmetrically for the wave magnetic field. • Both the sub-Alfvénic and super-Alfvénic solitons exist in the weakly relativistic regime. • Only sub-Alfvénic solitons exist in the ultrarelativistic regime. Nonlinear propagation of purely stationary large amplitude electromagnetic (EM) solitary waves in a magnetized electron–positron (EP) plasma is studied using a fully relativistic two-fluid hydrodynamic model which accounts for physical regimes of both weakly relativistic (P ≪ nmc 2) and ultrarelativistic (P ≫ nmc 2) random thermal energies. Here, P is the thermal pressure, n the number density and m the mass of a particle, and c is the speed of light in vacuum. While both the sub-Alfvénic and super-Alfvénic solitons coexist in the weakly relativistic regime, the ultrarelativistic EP plasmas in contrast support only the sub-Alfvénic solitons. Different limits of the Mach numbers and soliton amplitudes are also examined in these two physical regimes. [ABSTRACT FROM AUTHOR]

When high energy galactic cosmic ray (GCR) particles collide with the lunar regolith, they eject "albedo" particles from the surface. The albedo particles could be either scattered incident ions, or secondary ions and neutrons produced by the collisions of incident ions with the lunar regolith. In an effort to understand the nature of these albedo particles, we use the MCNP6 transport code to estimate the angular and energy distribution of albedo particles at an altitude of 50 km to calculate the resulting total absorbed dose rates, which are compared with measurements from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument aboard the Lunar Reconnaissance Orbiter (LRO) spacecraft. MCNP6 simulations estimate that the albedo particles account for 19.9% of the total absorbed dose rate. The albedo photons account for 8.81% of the total absorbed dose rate, the highest among albedo species followed by protons (4.97%), electrons (2.47%), positrons (1.89%), neutrons (1.17%), deuterons (0.5%), tritium ions (0.07%), helium-3 ions (0.02%), and alphas (0.01%). In addition, recent studies indicate the presence of hydrogen on the Moon. We simulate a hypothetical lunar regolith enriched with hydrogen to study its effect on the lunar albedo. The results herein show that the proton absorbed dose rate is slightly increased if hydrogen is present in the regolith, which is primarily caused by the increased flux of energetic albedo protons leaving the lunar surface. • Understanding the effects of albedo radiation is important for lunar discovery. • MCNP6 estimates that albedo particles contribute ~20% of the total absorbed dose. • Albedo photons account for 9% of the absorbed dose, the highest among albedo species. • The estimated dose rates are within 5% of those measured by the CRaTER instrument. [ABSTRACT FROM AUTHOR]

• Damped structures with critical behaviors in a four-component plasma fluid having positive and negative ions, non-thermal distributed positrons and electrons have been examined for related Earth's ionosphere plasma parameters. • Effects of the positron density ratio, ionic mass ratio, electron density ratio, the index of non-thermality on the formation of both damped structures of compressive and rarefactive types are studied. • The results performed in this work may be usable in the plasma of (D-F) Earth's ionosphere regions. The damped solitary structure characteristics in plasma model contains two fluid ions refers to positive and negative pairs, superthermal positrons and electrons density distributions have been considered. The damped two dimensional Kadomtsev–Petviashvili (DKP) equation has been gained from the plasma model. The nonlinear conditions of critical DKP are studied for parameters concerning the ionosphere plasma of Earth's. Effects of the positron number ratio, ion masses ratio, electron number ratio, the superthermality index and frequency of collisional parameters on the figuration of both compressive and rarefactive damped structures are investigated. It is a prominence invokes to indicate that the produced results may be applicable in the space plasmas of (D-F) ionosphere of Earth's regions. [ABSTRACT FROM AUTHOR]

Here, the storage sites of hydrogen in FeCr alloy, namely (H, He)–V nano-clusters with open volume, have been investigated by first-principles calculations and positron annihilation spectroscopy. The positron lifetimes in the nano-clusters obtained by theoretical calculations and experiments were compared. These results suggest that positron is sensitive to the relative position of the gas atoms decorating the open volume; and a helium atom forms a more repulsive ion core than a hydrogen atom when it occupies the vacancy, resulting in a decrease in positron lifetime. Interpretation of the PAS data was successfully combined with theoretical calculations, and allowed us to determine the defect status in specimens after H/He irradiation with different implantation patterns. The speculated kinds of hydrogen storage sites formed after irradiation are summarized. For the He-ions pre-implanted situation, the helium-vacancy clusters or bubbles forming in advance may recombine with H atoms to form stable He–H–V complex. • Positron is sensitive to the relative position of the H atoms decorating the open volume. • Various point defect structures were modeled. • The lifetime values of positrons in various (H, He)-V complexes are given. • The kinds of defects formed after He/H sequential-ion irradiations are summarized. [ABSTRACT FROM AUTHOR]

The triclinic phase of the bismuth orthotantalate (β-BiTaO 4) exhibited strong anisotropy of thermal expansion in the temperature range of 25–750 °C. The character of the thermal expansion of β-BiTaO 4 changed radically near 200 °C, which was not observed in its isomorphic analog (β-BiNbO 4). In the same temperature range the electrical properties also exhibited the local extremum. Crystal structure of β-BiNbO 4 was refined at 25, 200, 400 and 600 °C from powder X-ray diffraction data. The role of bismuth lone-electron pair is discussed. β-BiTaO 4 has a potential to be used as a thermal expansion material. Unlabelled Image [ABSTRACT FROM AUTHOR]

Changes in the free volume of poly(tetrafluoroethylene-co-hexafluoropropylene) proton exchange membrane caused by the grafting of styrene and incorporation of a sulfonic acid group (-SO 3 H) was investigated by using a positron annihilation lifetime measurement. The free volume size of the film decreases because of not only the incorporation of -SO 3 H but also structural changes in hydrogen bonds during proton transportation. The decrease of free volume size leads to the close distribution of -SO 3 H; therefore, the performance of the proton exchange membrane increases with the increase of the degree of grafting. • Proton exchange membrane was fabricated from fluorinated polymer. • Free volume change was investigated by positron annihilation lifetime measurement. • Longest ortho -positronium (o -Ps) lifetime was shortened by the grafting and sulfonating. • Fraction of positrons annihilate as o -Ps was decreased by changes in the chemical structure of the membrane. [ABSTRACT FROM AUTHOR]

Gamma-ray polarization is one of the most promising tools to probe the universe at extreme conditions and search for new physics. The Alpha Magnetic Spectrometer (AMS) is a precision particle physics detector on the International Space Station. With its high accuracy thin silicon strip detectors and permanent magnet, AMS is unique to study the polarization of high energy gamma-rays. The detection of gamma-rays above a few hundreds of MeV typically utilize the electron–positron pair production process, and the key step is to reconstruct the vertex where gamma-ray converts into the electron–positron pair. We present a new vertex reconstruction algorithm that is based on an extended cellular automaton to determine the direction and energy information of gamma-rays from the electron and positron trajectories in the AMS tracker. The vertex reconstruction efficiency is significantly improved with the presented algorithm over the entire energy range above 100 MeV and reaches > 90% above 1 GeV. The fake rate is drastically reduced over the entire energy range and is reduced from ∼ 10 % to ∼ 3 % at 200 MeV. The presented algorithm will thus provide the basis for measuring gamma-ray polarization with AMS. [ABSTRACT FROM AUTHOR]

We study the radiative decay of X (3872) based on the assumption that X (3872) is regarded as a c c ‾ charmonium with quantum number J P C = 1 + + (J , P , C represent the spin, parity and charge conjugation, respectively). The form factors of X (3872) transitions to J / ψ γ and ψ ′ γ (ψ ′ denotes ψ (2 S) throughout the paper) are calculated in the framework of the covariant light-front quark model. The phenomenological wave function of a meson depends on the parameter β , whose inverse essentially describes the confinement scale. In the present work, the parameters β for the vector J / ψ and ψ ′ mesons will be determined through their decay constants, which are obtained from the experimental values of their partial decay widths to the electron-positron pair. For X (3872) , we determined the value of β by the decay width of X (3872) → ψ ′ γ. Then, we examined the width of X (3872) → J / ψ γ in a manner of parameter-free prediction and compared it with the experimental value. As a result, an inconsistency or contradiction occurs between the widths of X (3872) → J / ψ γ and X (3872) → ψ ′ γ. We thus conclude that X (3872) cannot be a pure c c ‾ resonance and that other components are necessary in its wave function. [ABSTRACT FROM AUTHOR]

The FASER experiment at the LHC is designed to search for light, weakly-interacting particles produced in proton-proton collisions at the ATLAS interaction point that travel in the far-forward direction. The first results from a search for dark photons decaying to an electron-positron pair, using a dataset corresponding to an integrated luminosity of 27.0 fb − 1 collected at centre-of-mass energy s = 13.6 TeV in 2022 in LHC Run 3, are presented. No events are seen in an almost background-free analysis, yielding world-leading constraints on dark photons with couplings ϵ ∼ 2 × 10 − 5 − 1 × 10 − 4 and masses ∼ 17 MeV − 70 MeV. The analysis is also used to probe the parameter space of a massive gauge boson from a U(1) B − L model, with couplings g B − L ∼ 5 × 10 − 6 − 2 × 10 − 5 and masses ∼ 15 MeV − 40 MeV excluded for the first time. [ABSTRACT FROM AUTHOR]

Observation of efficient Breit-Wheeler electron-positron pair creation is one of the main goals for modern-day strong laser-particle experiments. We propose exploring this process by colliding plasma-generated harmonics, from currently available laser pulses, with a beam of GeV photons. We show that the creation yield is enhanced for more than one order of magnitude, compared with the yield obtained without high-harmonic generation. The robustness of the yield enhancement is demonstrated by considering multiple interaction parameters and the potential photon source for the upcoming experiments. Moreover, we show that due to the evident field asymmetry of the plasma-generated harmonics, the averaged spin-polarization of the created pairs could be as high as 62%. [ABSTRACT FROM AUTHOR]

The study of defect chemistry for doped BaZrO 3 proton conductors is of particular interest because of defect interactions that can affect the proton conductivity of the material. Protons incorporated due to the material's hydration can be trapped by negatively charged immobile dopants, reducing proton mobility. The reduction of the proton conduction impedes the use of BaZrO 3 materials in energy conversion applications at intermediate temperatures (300 °C – 600 °C). The probing of proton trapping in doped BaZrO 3 is hindered by the limited availability of techniques sensitive to defect chemistries. In this work, we used positron annihilation lifetime spectroscopy (PALS) to study the defect chemistry of Y-doped and Sc-doped BaZrO 3. Using a two-state positron trapping model we showed that PALS can be applied to study the defect chemistry of hydrated dense proton conductors. Positron trapping rates and lifetimes were correlated with doping levels of the materials. Probability significance t -tests were carried out for PALS parameters to verify whether there are differences/similarities for various populations: non-doped/doped, level and type of doping, high temperature, and surface effects. The results revealed that the initial doping generates a significant number of traps available for positrons. Doping with yttrium increased the positron trapping rate, while this effect was not observed with scandium. Low-temperature hydration affects specimens significantly inhibiting positron trapping at undoped BaZrO 3 material and highly doped specimens. Positronium formation in rough surface layers, and highly doped specimens was detected but does not exceed 1%. [ABSTRACT FROM AUTHOR]

Very high energy (VHE) gamma and cosmic rays scatter with the atmospheric nuclei and create an extensive air shower (EAS) of electrons and positrons, which travel with relativistic speeds and induce the medium to emit a flash of Cherenkov light, which is detected by the camera. This indirect method to detect EAS is known as the imaging atmospheric Cherenkov technique (IACT). However, the main challenge in IACT is to segregate the EAS events induced by gamma primaries from huge cosmic ray background events. Since cosmic background events are ∼ 1 0 3 times more abundant than gamma rays, the gamma-cosmic ray discrimination plays a crucial role in evaluating the sensitivity of an IACT telescope, like the TACTIC. There are several methods to reduce the dimensionality of Cherenkov event images, such as principal component analysis (PCA), gamma domain dynamic supercuts and machine learning-based cuts which classify the gamma or hadronic events. In this study, we report applying a novel dimensionality reduction technique t-SNE (t-distributed stochastic neighbour embedding), on the image parameters of EASs. This technique enables us to visualize complex multi-dimensional features of EAS images into a compressed two-dimensional projection while preserving local neighbourhood features of the higher dimension. The efficacy of dimensionality reduction, which in this case is measured in terms of the statistical significance of detecting gamma-ray signal over cosmic ray background, is compared with the significance obtained using the conventional dynamic supercuts method. The application of the t-SNE technique to estimate signals from TACTIC observation data is also presented. [Display omitted] • Correlations among image parameters for different primary particles are nonlinear. • t-SNE preserves correlations among image parameters for similar species of events. • Gamma and cosmic ray discrimination are crucial for an IACT telescope's sensitivity. • t-SNE method outperforms conventional dynamic cuts to retrieve gamma-ray signals. [ABSTRACT FROM AUTHOR]

The non-conventional (hybrid) scheme of a positron source using GeV electron beams is investigated by means of our Mathematica and GEANT4 simulation codes. Axial channeling radiation (CR) is generated in a Si single crystal (radiator) and subsequently converted into e+–e− pairs in an amorphous tungsten (W) target (converter). We will present numerical calculations of axial CR spectra from relativistic electrons of different energies channeled in a Si single crystal. Applying both the dipole and non-dipole approach, comparison reveals a striking difference between obtained energy distributions of axial CR. Positron spectra obtained by pair production and captured by an adiabatic matching device (AMD) are simulated using GEANT4 toolkit. The AMD provides an axial magnetic field of upstream decreasing strength between the converter and the aperture of some pre-accelerating structure (linac). We also present Monte-Carlo simulation results of positron-beam emittance and transverse beam-density distribution behind the W converter and behind the AMD. [ABSTRACT FROM AUTHOR]

The ablation of a target, composed of a homogeneous mixture of Fe & Co metal with H 3 BO 3 powder, produces core-shell type particles on the as-deposited coating surface. Annealing at 600 °C in air transforms the core-shell into urchin-like particles having nanowires of 10–30 nm in diameter and 0.5–1 μm in length, grown radially from the particle surface as a result of the stress created between core and shell. Microstructural and analytical characterization confirms that nanowires are composed of CoFe 2 O 4 and CoO phases forming a heterojunction, which showed outstanding performance as a photocatalyst, requiring half the time for an organic water pollutant degradation reaction in comparison to similarly nanostructured single-metal oxide counterparts (Co 3 O 4 and Fe 2 O 3). Degradation reactions conducted in controlled conditions demonstrate that the urchin-like mixed oxide coatings are highly efficient both in direct photocatalysis and in photo-Fenton reaction. This overall enhancement in activity is due to a synergistic effect created at the heterojunction of CoFe 2 O 4 /CoO that allows the formation of a Z -scheme mechanism to facilitate the spatial separation of photoinduced electron-hole pairs. Moreover, the hierarchical urchin-like nanostructures provide a large number of active sites for photocatalytic reactions, while the lower band gap of CoFe 2 O 4 permits better visible light absorption to effectively degrade organic pollutants even under visible light. Based on all the results, a plausible reaction mechanism is proposed related to Z -scheme heterojunction formed with CoFe 2 O 4 /CoO. Unlabelled Image • A coating of urchin-like nanostructured CoFe 2 O 4 /CoO heterojunction is synthesized by PLD. • Implementation of a Z-scheme design greatly improves charge separation. • Hierarchical nanostructuring provides large number of active sites for photocatalytic reactions. • The coating shows outstanding photocatalytic activity towards a model pollutant. [ABSTRACT FROM AUTHOR]

Electron-positron pair production from vacuum in a strong electric field oscillating in time is studied. The field is assumed to consist of two consecutive pulses, with variable time delay in between. Pair production probabilities are obtained by numerical solution of the corresponding time-dependent Dirac equation. Considering symmetric field configurations comprising two identical pulses, we show that the pulse distance strongly affects the momentum spectra of produced particles and even the total production probability. Conversely, in a highly asymmetric situation when the field contains low-intensity prepulse and high-intensity main pulse, we identify a range of field parameters where the prepulse despite its weakness can leave visible traces in the particle spectra. [ABSTRACT FROM AUTHOR]

We calculate cross sections of a pair B c meson production on the basis of two-photon mechanism from electron-positron annihilation. We investigate the production cross sections in nonrelativistic approximation and with the account of relativistic corrections. Relativistic production amplitudes of S-wave pair pseudoscalar, vector and pseudoscalar+vector B c -mesons are constructed on the basis of relativistic quark model. Numerical values of the production cross sections are obtained at different center-of-mass energies. The comparison of one-photon and two-photon annihilation contributions is presented. [ABSTRACT FROM AUTHOR]

A start-to-end optimization simulation toolkit for the CLIC positron source has been developed using multiple simulation codes to model adequately different areas of the positron source. The positron source includes the targets using channeling and pair-production processes, the adiabatic matching device and the pre-injector and injector linacs. The primary electron beams with energies of 5 GeV and 3 GeV are optimized with this toolkit as well as the target parameters. Finally rf parameters or the linear accelerators are optimized involving a particle tracking code. Using this approach the yield of the CLIC positron source has been increased by a factor 2 resulting in significant cost savings. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Pore size of SBA-15 can be tuned from 6.5 nm to 17.2 nm by adding TMB swelling agent. • The pore morphology changes in three stages with increasing TMB/P123 ratio. • The size of the micropore estimated by o -Ps lifetime. • PALS measured in vacuum and air can determine whether the pores are open or closed. • The results of mesopore size estimated from PALS and gas adsorption were compared. Abstract Porous silica SBA-15 was synthesized using triblock copolymer P123 as structure template and tetraethyl orthosilicate (TEOS, C 8 H 20 O 4 Si) as silicon source. The pore structure was adjusted by using swelling agent 1,3,5-trimethylbenzene (TMB). Small angle X-ray scattering (SAXS) and high resolution transmission electron microscopy (HRTEM) indicate that the pore morphology changes in three stages with increasing TMB/P123 ratio. In the first stage (TMB/P123 < 0.2), the pore type is a typical cylindrical hole. When TMB/P123 is 0.2–0.5, the pore morphology is a curved cylinder. In the final stage when TMB/P123 ratio is higher than 0.5, the ordered mesoporous silica is converted into mesoporous silica foam. The average pore size estimated from N 2 adsorption measurements increases from 6.5 nm to 17.2 nm with increasing TMB/P123 ratio from 0 to 2. Positron lifetime measurements indicates two long lifetime components τ 3 and τ 4 , which are due to o -Ps annihilation in micropores and mesopores, respectively. It was found that the mesopores are open pores and the micropores are closed pores. With the increase of TMB ratio, the number and size of micropores show nearly no change, but the mesopore size increases gradually with increasing TMB/P123 ratio up to 0.5, which are in agreement with the results of the N 2 adsorption/desorption measurements. However after the pores evolves into mesoporous foam, the pore size obtained from o -Ps lifetime is less than that of N 2 adsorption/desorption measurements. [ABSTRACT FROM AUTHOR]

Abstract Carbon (C) is used to increase the overall performance of Ge-Sb-Te (GST) phase-change memory material. Yet the C configuration in polycrystalline GST and its microscopic role is unclear. Using the well-studied GeSb 2 Te 4 as an example, this work unravels the microscopic C doping role based on ab initio calculations. Our results reveal that carbon prefers occupying the interstitials at very low C concentrations, while with a roughly critical C concentration of over 2%, carbon atoms will cluster at the grain boundaries, with very few carbon atoms might exist at the interstitials. With further increasing the C concentrations, C atoms tend to form ring-like configurations in the grain boundaries rather than chain-like configurations. This is due to that the covalent bonds in ring-like configurations are stronger than that in chain-like configurations. Further analysis on the lone-pair electrons and electronic densities of states show that C dopants significantly change the number of lone-pair electrons of surrounding atoms, thus affecting the electronic structure. Finally, the diffusion coefficient of C is estimated to be of the order of 10−13 m2/s at 400 K, indicating the good stability of C dopants in GeSb 2 Te 4. Our work provides fundamental understanding on the microscopic role of C doping in GST phase-change materials and benefits for improving the properties of the recording materials by controlling the doping concentration. Highlights • Carbon will randomly occupy the interstitials below a concentration around 2%. • Carbon will cluster at the grain boundaries when the concentration over 2%. • Carbon-rings at the grain boundaries are the most stable configuration. • C affects electronic structures by changing neighboring lone-pair electrons. • C doped polycrystalline GST phase-change material has good stability. [ABSTRACT FROM AUTHOR]

Abstract DAMPE (DArk Matter Particle Explorer) is a spaceborne high-energy cosmic ray and gamma-ray detector, successfully launched in December 2015. It is designed to probe astroparticle physics in the broad energy range from few GeV to 100 TeV. The scientific goals of DAMPE include the identification of possible signatures of Dark Matter annihilation or decay, the study of the origin and propagation mechanisms of cosmic-ray particles, and gamma-ray astronomy. DAMPE consists of four sub-detectors: a plastic scintillator strip detector, a Silicon–Tungsten tracKer–converter (STK), a BGO calorimeter and a neutron detector. The STK is composed of six double layers of single-sided silicon micro-strip detectors interleaved with three layers of tungsten for photon conversions into electron–positron pairs. The STK is a crucial component of DAMPE, allowing to determine the direction of incoming photons, to reconstruct tracks of cosmic rays and to estimate their absolute charge (Z). We present the in-flight performance of the STK based on two years of in-flight DAMPE data, which includes the noise behavior, signal response, thermal and mechanical stability, alignment and position resolution. [ABSTRACT FROM AUTHOR]

Abstract Single-shot positron annihilation lifetime spectroscopy (SSPALS) is an extremely useful tool for experiments involving the positronium atom (Ps). I examine some of the methods that are typically employed to analyse lifetime spectra, and use a Monte-Carlo simulation to explore the advantages and limitations these have in laser spectroscopy experiments, such as resonance-enhanced multiphoton ionization (REMPI) or the production of Rydberg Ps. [ABSTRACT FROM AUTHOR]

Abstract Electron antineutrinos are detected in organic liquid scintillator based neutrino experiments by means of the inverse beta decay, producing both a positron and a neutron. The positron may form a bound state together with an electron, called positronium (Ps). The longer-lived spin state of Ps, orthopositronium (o-Ps) has a lifetime of about 3 ns in organic liquid scintillators (LS). Its formation changes the time distribution of photon emission, which affects positron reconstruction algorithms and allows the application of pulse shape discrimination (PSD) to distinguish electron from positron events. In this work we measured the lifetime τ 2 and formation probability I 2 of o-Ps in the linear alkylbenzene (LAB) based LS of the JUNO (Jiangmen Underground Neutrino Observatory) experiment including wavelength shifters, obtaining τ 2 = 2. 98 ns ± 0. 05 ns and I 2 = 44 % ± 3 %. We are using a novel type of setup, which allows for additional means of background suppression compared to commonly used PALS (positron annihilation lifetime spectroscopy) measurement setups. [ABSTRACT FROM AUTHOR]

The STAR collaboration has observed an excess production of electron-positron pairs which have transverse momenta p ⊥ < 150 MeV/c in peripheral gold-gold and uranium-uranium collisions. ALICE has also reported on an excess of μ + μ − pairs at low p ⊥ in very peripheral (70–90% centrality) lead-lead collisions at a center-of-mass energy of 2.76 TeV/nucleon pair. These excesses cannot be explained by the QGP thermal radiation and ρ in-medium broadening calculations. This is a sign of coherent photon–photon interactions in ultra-peripheral collisions. However, the number of lepton pair production is more than the predictions from hadronic production models. In literature, there are number of explanations about the p ⊥ broadening, however none of them has included the multi-pair production processes in their calculations. The aim of this paper is to show that at RHIC and LHC energies and for small impact parameters unitarity is violated and lowest order calculations are not adequate to calculate electromagnetic lepton pair production. Therefore, we have to include higher order effects in the calculations. We have shown that electron-positron multi-pair production cross section is large and it cannot be ignored in explaining the excess production of electron-positron pairs for low transverse momenta. [ABSTRACT FROM AUTHOR]

We calculate hard spin-independent contributions to energy levels in muonium and positronium which are due to radiatively corrected electron factor insertion in two-photon exchange diagrams. Calculation of these corrections is motivated by the new round of precise measurements of spin-independent transition frequencies in muonium and positronium. [ABSTRACT FROM AUTHOR]

The first measurements of the Fourier coefficients (V n Δ) of the azimuthal distributions of charged hadrons emitted from photon-proton (γp) interactions are presented. The data are extracted from 68.8 nb−1 of ultra-peripheral proton-lead (pPb) collisions at s NN = 8.16 TeV using the CMS detector. The high energy lead ions produce a flux of photons that can interact with the oncoming proton. This γp system provides a set of unique initial conditions with multiplicity lower than in photon-lead collisions but comparable to recent electron-positron and electron-proton data. The V n Δ coefficients are presented in ranges of event multiplicity and transverse momentum (p T) and are compared to corresponding hadronic minimum bias pPb results. For a given multiplicity range, the mean p T of charged particles is smaller in γp than in pPb collisions. For both the γp and pPb samples, V 1 Δ is negative, V 2 Δ is positive, and V 3 Δ consistent with 0. For each multiplicity and p T range, V 2 Δ is larger for γp events. The γp data are consistent with model predictions that have no collective effects. [ABSTRACT FROM AUTHOR]

Structure based wakefield acceleration may provide a viable approach for accelerating sufficiently large numbers of electrons and positrons at the high gradient needed to meet the luminosity, efficiency, and cost requirements of a future linear collider. An important step in proving its viability is the demonstration of acceleration in multiple stages. Here we show the results of the first experimental demonstration of staged two beam wakefield acceleration, conducted at the Argonne Wakefield Accelerator Facility (AWA), in which a 0.5 nC electron bunch gained equal amounts of energy in two stages ( ∼ 2.4 MeV per stage, corresponding to an average acceleration gradient of ∼ 70 MeV/m). Meanwhile 150MeV/m of acceleration in a single stage has been achieved. The demonstration experiment should be scalable to staged-acceleration at gradients of the order of 200 to 300 MeV/m. Such a development would considerably reduce both the cost and footprint of both a future high-energy physics (HEP) collider, as well as future X-ray light sources. [ABSTRACT FROM AUTHOR]

In this study, we have located a new P o 1 shape resonance in positronium ion lying above the Ps( N = 3 ) threshold using the complex coordinate rotation method based on correlated exponential wave functions. To trace this shape resonance pole from H − to Ps − , we have calculated the shape resonance in terms of nuclear mass by changing the mass of the positively charged particle from infinitely heavy to one unit of the electron mass. The P o 1 shape resonance in H − lying above the H( N = 3 ) threshold is in accord with the available data in the literature. Our present findings are useful references for future experimental investigations to observe this new shape resonance in Ps − . The present work is also of interest in various research areas such as nuclear physics and semiconductor quantum dots including excitons. [ABSTRACT FROM AUTHOR]

The electron and positron chemical potentials, positron affinity and bulk lifetime as well as the positronium work function in InP are investigated. The emphasis of this work is on the hydrostatic pressure effect on these features. The calculations are performed with a pseudopotential approach and the independent particle model. All parameters of interest are found to vary monotonically with pressure. Our findings showed that under compression the positron annihilates differently in InP semiconductor compound. At zero pressure, the positron bulk lifetime is calculated to be 243.47 ps. However, upon compression it decreases almost linearly suggesting the decrease of the crystal ionicity under applied pressure. The positronium work function is found to increase with raising pressure which indicates that under compression less positronium atoms will be formed in InP sample surface and ejected into the vacuum. The parameters investigated in the present work are important in slow-positron-beam experiments. [ABSTRACT FROM AUTHOR]

High intensity of particle beams is crucial for high-performance operation of modern electron–positron storage rings, both colliders and light sources. The beam intensity is limited by the interaction of the beam with self-induced electromagnetic fields (wake fields) proportional to the vacuum chamber impedance. For a new accelerator project, the total broadband impedance is computed by element-wise wake-field simulations using computer codes. For a machine in operation, the impedance can be measured experimentally using beam-based techniques. In this article, a comparative analysis of impedance computations and beam-based measurements is presented for 15 electron–positron storage rings. The measured data and the predictions based on the computed impedance budgets show a significant discrepancy. Three possible reasons for the discrepancy are discussed: interference of the wake fields excited by a beam in adjacent components of the vacuum chamber, effect of computation mesh size, and effect of insufficient bandwidth of the computed impedance. [ABSTRACT FROM AUTHOR]