Explore the vast range of titles available.

Laser–electron beam collisions that aim to generate electron–positron pairs require laser intensities I ≳ 1021 W cm−2, which can be obtained by focusing a 1-PW optical laser to a spot smaller than 10 μm. Spatial synchronization is a challenge because of the Poynting instability that can be a concern both for the interacting electron beam (if laser-generated) and the scattering laser. One strategy to overcome this problem is to use an electron beam coming from an accelerator (e.g., the planned E-320 experiment at FACET-II). Even using a stable accelerator beam, the plane wave approximation is too simplistic to describe the laser–electron scattering. This work extends analytical scaling laws for pair production, previously derived for the case of a plane wave and a short electron beam. We consider a focused laser beam colliding with electron beams of different shapes and sizes. The results take the spatial and temporal synchronization of the interaction into account, can be extended to arbitrary beam shapes, and prescribe the optimization strategies for near-future experiments.

The generation of electron–positron pairs from the interaction of laser radiation with a flat overcritical target (foil) is studied. The parameters of the generated pairs such as their number, density, spectrum and angular distribution are determined using full-scale three-dimensional particle-in-cell simulation taking into account quantum-electrodynamic (QED) effects. Two interaction configurations are investigated based on focusing six laser pulses onto a solid target with parameters expected at the XCELS laser facility. The configurations are not optimum in terms of the parameters ultimately achievable at this facility but they are reliable and quite simple in terms of practical feasibility. It is shown that even in these configurations it is possible to generate electron–positron pairs with energies up to GeV units, the total number of pairs exceeding 10 11 , and with an average density of 2 × 10 20 cm –3 . Generating electron–positron plasma with such parameters opens up opportunities for laboratory investigation of some astrophysical phenomena.

Using the Dirac–Heisenberg–Wigner formalism, effects of the asymmetric pulse shape on the generation of electron-positron pairs in three typical polarized fields, i.e., linear, middle elliptical and circular fields, are investigated. Two kinds of asymmetries for the falling pulse length, short and elongated, are studied. We find that the interference effect disappears with the shorter pulse length and that the peak value of the momentum spectrum is concentrated in the center of the momentum space. In the case of the extending falling pulse length, a multiring structure without interference appears in the momentum spectrum. Research results show that the momentum spectrum is very sensitive to the asymmetry of the pulse as well as to the polarization of the fields. We also find that the number density of electron-positron pairs under different polarizations is sensitive to the asymmetry of the electric field. For the short falling pulse, the number density can be significantly enhanced by over two orders of magnitude. These results could be useful in planning high-power and/or high-intensity laser experiments.

Electron–positron pair production via the nonlinear Bethe–Heitler effect in the combined fields of a bare nucleus and a high-intensity laser pulse is studied theoretically. The calculations are performed within the framework of strong-field quantum electrodynamics using a flat-top laser profile with raising and falling edges. This way, the dependence of the pair production process on the precise shape of the laser field is analyzed. Our approach allows us, in particular, to follow the evolution of the created particles’ energy spectra from ultra-short few-cycle pulses to the monochromatic infinite pulse-train limit. We show how the various portions of the pulse influence these spectra and determine conditions for which the outcome from a laser pulse closely resembles the predictions from monochromatic theory.

Within the framework of the Standard Model, the differential cross section of the process e – e + → ZHH is calculated taking into account arbitrary polarizations of the electron-positron pair. The characteristic features in the behavior of the cross section and polarization characteristics (left-right and transverse spin asymmetries) are investigated and revealed depending on the emission angles and energies of particles.

Electromagnetic cascades have the potential to act as a high-energy photon source of unprecedented brightness. Such a source would offer new experimental possibilities in fundamental science, but in the cascade process radiation reaction and rapid electron-positron plasma production seemingly restrict the efficient production of photons to sub-GeV energies. Here, we show how to overcome these energetic restrictions and how to create a directed GeV photon source, with unique capabilities as compared to existing sources. Our new source concept is based on a controlled interplay between the cascade and anomalous radiative trapping. Using specially designed advanced numerical models supported with analytical estimates, we demonstrate that the concept becomes feasible at laser powers of around 7 PW, which is accessible at soon-to-be-available facilities. A higher peak power of 40 PW can provide 109 photons with GeV energies in a well-collimated 3-fs beam, achieving peak brilliance 9×1024phs−1mrad−2mm−2/0.1%BW .

The process of a resonant production of an ultrarelativistic electron–positron pair in the process of gamma-quantum scattering in the X-ray field of a pulsar is theoretically studied. This process has two reaction channels. Under resonant conditions, an intermediate electron (for a channel A) or a positron (for a channel B) enters the mass shell. As a result, the initial second-order process of the fine-structure constant in the X-ray field effectively splits into two first-order processes: the X-ray field-stimulated Breit–Wheeler process and the the X-ray field-stimulated Compton effect on an intermediate electron or a positron. The resonant kinematics of the process is studied in detail. It is shown that for the initial gamma quantum there is a threshold energy, which for the X-ray photon energy (1–102) keV has the order of magnitude (103–10) MeV. In this case, all the final particles (electron, positron, and final gamma quantum) fly in a narrow cone along the direction of the initial gamma quantum momentum. It is important to note that the energies of the electron–positron pair and the final gamma quantum depend significantly on their outgoing angles. The obtained resonant probability significantly exceeds the non-resonant one. The obtained results can be used to explain the spectrum of positrons near pulsars.

Relativistic electron-positron plasmas are ubiquitous in extreme astrophysical environments such as black-hole and neutron-star magnetospheres, where accretion-powered jets and pulsar winds are expected to be enriched with electron-positron pairs. Their role in the dynamics of such environments is in many cases believed to be fundamental, but their behavior differs significantly from typical electron-ion plasmas due to the matter-antimatter symmetry of the charged components. So far, our experimental inability to produce large yields of positrons in quasi-neutral beams has restricted the understanding of electron-positron pair plasmas to simple numerical and analytical studies, which are rather limited. We present the first experimental results confirming the generation of high-density, quasi-neutral, relativistic electron-positron pair beams using the 440 GeV/c beam at CERN’s Super Proton Synchrotron (SPS) accelerator. Monte Carlo simulations agree well with the experimental data and show that the characteristic scales necessary for collective plasma behavior, such as the Debye length and the collisionless skin depth, are exceeded by the measured size of the produced pair beams. Our work opens up the possibility of directly probing the microphysics of pair plasmas beyond quasi-linear evolution into regimes that are challenging to simulate or measure via astronomical observations. Relativistic electron-positron (pair) plasmas play a fundamental role in the magnetospheres, jets, and winds of black holes and neutron stars, but existing studies have been purely theoretical. Here, the authors open up the exciting possibility to probe relativistic pair-plasmas in the laboratory.

The workshop “Shedding light on X17” brings together scientists looking for the existence of a possible new light particle, often referred to as X17. This hypothetical particle can explain the resonant structure observed at ∼  17 MeV in the invariant mass of electron-positron pairs, produced after excitation of nuclei such as 8 Be and 4 He by means of proton beams at the Atomki Laboratory in Debrecen. The purpose of the workshop is to discuss implications of this anomaly, in particular theoretical interpretations as well as present and future experiments aiming at confirming the result and/or at providing experimental evidence for its interpretation.

A bstract Reactor neutrino experiments provide a rich environment for the study of axionlike particles (ALPs). Using the intense photon flux produced in the nuclear reactor core, these experiments have the potential to probe ALPs with masses below 10 MeV. We explore the feasibility of these searches by considering ALPs produced through Primakoff and Compton-like processes as well as nuclear transitions. These particles can subsequently interact with the material of a nearby detector via inverse Primakoff and inverse Compton-like scatterings, via axio-electric absorption, or they can decay into photon or electron-positron pairs. We demonstrate that reactor-based neutrino experiments have a high potential to test ALP-photon couplings and masses, currently probed only by cosmological and astrophysical observations, thus providing complementary laboratory-based searches. We furthermore show how reactor facilities will be able to test previously unexplored regions in the ∼MeV ALP mass range and ALP-electron couplings of the order of g aee ∼ 10 − 8 as well as ALP-nucleon couplings of the order of g ann 1 ∼ 10 −9 , testing regions beyond TEXONO and Borexino limits.