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The interaction of light with the quantum-vacuum is predicted to give rise to some of the most fundamental and exotic processes in modern physics, which remain untested in the laboratory to date. Electron–positron pair production from a pure vacuum target, which has yet to be observed experimentally, is possibly the most iconic. The advent of ultra-intense lasers and laser accelerated GeV electron beams provide an ideal platform for the experimental realisation. Collisions of high energy γ-ray photons derived from the GeV electrons and intense laser fields result in detectable pair production rates at field strengths that approach and exceed the Schwinger limit in the centre-of-momentum frame. A detailed experiment has been designed to be implemented at the ATLAS laser at the centre of advanced laser applications. We show full calculations of the expected backgrounds and beam parameters which suggest that single pair events can be reliably generated and detected.

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.

The forthcoming generation of multi-petawatt lasers opens the way to abundant pair production by the nonlinear Breit–Wheeler process, i.e. the decay of a photon into an electron–positron pair inside an intense laser field. In this paper we explore the optimal conditions for Breit–Wheeler pair production in the head-on collision of a laser pulse with gamma photons. The role of the laser peak intensity versus the focal spot size and shape is examined keeping a constant laser energy to match experimental constraints. A simple model for the soft-shower case, where most pairs originate from the decay of the initial gamma photons, is derived. This approach provides us with a semi-analytical model for more complex situations involving either Gaussian or Laguerre–Gauss (LG) laser beams. We then explore the influence of the order of the LG beams on pair creation. Finally we obtain the result that, above a given threshold, a larger spot size (or a higher order in the case of LG laser beams) is more favorable than a higher peak intensity. Our results match very well with three-dimensional particle-in-cell simulations and can be used to guide upcoming experimental campaigns.

We have repeated the experiment performed recently by ATOMKI Laboratory (Debrecen, Hungary), which may indicate a new particle called X17 in the literature. In order to obtain a reliable and independent result, we used a different structure of the electron–positron pair spectrometer at the VNU University of Science. The spectrometer has two arms and simpler acceptance and efficiency as a function of the correlation angle, but the other conditions of the experiment were very similar to the published ones. We could confirm the presence of the anomaly measured at E[sub.p] = 1225 keV, which is above the E[sub.p] = 1040 keV resonance.

It is conjectured that all perturbative approaches to quantum electrodynamics (QED) break down in the collision of a high-energy electron beam with an intense laser, when the laser fields are boosted to 'supercritical' strengths far greater than the critical field of QED. As field strengths increase toward this regime, cascades of photon emission and electron-positron pair creation are expected, as well as the onset of substantial radiative corrections. Here we identify the important role played by the collision angle in mitigating energy losses to photon emission that would otherwise prevent the electrons reaching the supercritical regime. We show that a collision between an electron beam with energy in the tens of GeV and a laser pulse of intensity 10 24 W cm − 2 at oblique, or even normal, incidence is a viable platform for studying the breakdown of perturbative strong-field QED. Our results have implications for the design of near-term experiments as they predict that certain quantum effects are enhanced at oblique incidence.

Measuring signatures of strong-field quantum electrodynamics (SF-QED) processes in an intense laser field is an experimental challenge: it requires detectors to be highly sensitive to single electrons and positrons in the presence of the typically very strong x-ray and γ -photon background levels. In this paper, we describe a particle detector capable of diagnosing single leptons from SF-QED interactions and discuss the background level simulations for the upcoming Experiment-320 at FACET-II (SLAC National Accelerator Laboratory). The single particle detection system described here combines pixelated scintillation LYSO screens and a Cherenkov calorimeter. We detail the performance of the system using simulations and a calibration of the Cherenkov detector at the ELBE accelerator. Single 3 GeV leptons are expected to produce approximately 537 detectable photons in a single calorimeter channel. This signal is compared to Monte-Carlo simulations of the experiment. A signal-to-noise ratio of 18 in a single Cherenkov calorimeter detector is expected and a spectral resolution of 2% is achieved using the pixelated LYSO screens.

Recently, when examining the differential internal pair creation coefficients of 8Be, 4He and 12C nuclei, we observed peak-like anomalies in the angular correlation of the e+e− pairs. This was interpreted as the creation and immediate decay of an intermediate bosonic particle with a mass of mXc2≈ 17 MeV, receiving the name X17 in subsequent publications. In this paper, our latest results obtained for the X17 particle are presented by investigating the e+e− pair correlations in the decay of the Giant Dipole Resonance (GDR) of 8Be. Our results initiated a significant number of new experiments all over the world to detect the X17 particle and determine its properties. In this paper, we will also conduct a mini-review of the experiments whose results are already published, as well as the ones closest to being published.

We have repeated the experiment performed recently by ATOMKI Laboratory (Debrecen, Hungary), which may indicate a new particle called X17 in the literature. In order to obtain a reliable and independent result, we used a different structure of the electron–positron pair spectrometer at the VNU University of Science. The spectrometer has two arms and simpler acceptance and efficiency as a function of the correlation angle, but the other conditions of the experiment were very similar to the published ones. We could confirm the presence of the anomaly measured at Ep = 1225 keV, which is above the Ep = 1040 keV resonance.

A mechanism of high energy and high density positron beam creation is proposed in ultra-relativistic laser-plasma interaction. Longitudinal electron self-injection into a strong laser field occurs in order to maintain the balance between the ponderomotive potential and the electrostatic potential. The injected electrons are trapped and form a regular layer structure. The radiation reaction and photon emission provide an additional force to confine the electrons in the laser pulse. The threshold density to initiate the longitudinal electron self-injection is obtained from analytical model and agrees with the kinetic simulations. The injected electrons generate γ-photons which counter-propagate into the laser pulse. Via the Breit-Wheeler process, well collimated positron bunches in the GeV range are generated of the order of the critical plasma density and the total charge is about nano-Coulomb. The above mechanisms are demonstrated by particle-in-cell simulations and single electron dynamics.

Within the quantum field theory approach and using the technique of Bogoliubov transformations, the von Neumann boson-antiboson pair creation quantum entanglement entropy is studied in the context of the noncommutative Bianchi I universe. The investigations have shown that the behavior of entanglement entropy is strongly influenced by the choice of the noncommutativity θ parameter, k ⊥ -frequency modes and the structure of the curved spacetime. Moreover, the relationship between thermodynamics, Bose–Einstein condensation and quantum entanglement is also discussed.