Compton-like dark photon production in electron-nucleus collisions

The Compton-like production of massive dark photons is investigated in ultrarelativistic electron-ion collisions considering the kinetic mixing between the dark photon and the Standard Model photon. The quasi-real photons in the heavy ion are described by the EPA approximation and the model is employed to calculate the integrated cross section and event rates as a function of the dark photon mass, mγ′, and mixing parameter, ε. Predictions are shown for electron-ion colliders (EICs) in the mass range 100 ≤ mγ′ ≤ 500 MeV. Numerical results are provided within the kinematic coverage of the planned machines Electron-ion collider in China (EicC), A Polarized Electron-Ion Collider at Jefferson Lab (JLEIC), Electron Ion Collider/USA (EIC), Large Hadron Electron Collider (LHeC) and Future Circular Collider (FCC-eA). It complements existing search strategies for dark photons in the considered mass interval.

Resonant Production of an Ultrarelativistic Electron–Positron Pair at the Gamma Quantum Scattering by a Field of the X-ray Pulsar

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.