We find a zero in the positronium formation scattering amplitude and deep minimum logarithm of corresponding differential cross section for positron–helium collisions an energy just above threshold. Corresponding to zero, there is vortex extended velocity field that associated with this when one treats both magnitude momentum incident positron angle scattered as independent variables. Using com...

By solving the Fokker-Planck equation directly we examine the effects of annihilation, particle escape and injection on the form of a steady-state positron distribution in thermal hydrogen plasmas with kT < mec. The positron fraction considered is small enough, so it does not affect the electron distribution which remains Maxwellian. We show that the escape of positrons in the form of electron-...

The cross section for production of R-parity violating squarks (q̃) or leptoquarks (LQ) with masses above 200 GeV by positron-proton scattering at HERA can be substantially increased by a moderate increase of the beam energies. If, for example, the positron energy is raised from 27.5 to 32.5 GeV and the proton energy from 820 to 1000 GeV, the q̃/LQ production cross section for masses of 200 – 230...

Positron initiated deeply virtual Compton scattering (DVCS) off $^4$He and $^3$He nuclei is described. The way the so-called $d-$term could be obtained from real part of relevant form factor summarized, importance novelty this measurement discussed. measurements addressed for targets very useful even in a standard unpolarized target setup, measuring beam spin charge asymmetries only. DVCS are a...

We apply the solution to the recursion relation for the double-off-shell quark current to the problem of computing one loop amplitudes with an arbitrary number of gluons. We are able to compute amplitudes for photon-gluon scattering, electron-positron annihilation to gluons, and gluon-gluon scattering via a quark loop in the case of like-helicity gluons. In addition, we present the result for t...

We analyze low-energy scattering of positrons on Ar atoms and N2 molecules using Modified Effective-Range Theory (MERT) developped by O’Malley, Spruch and Rosenberg [Journal of Math. Phys. 2, 491 (1961)]. We use formulation of MERT based on exact solutions of Schrödinger equation with polarization potential rather than low-energy expansions of phase shifts into momentum series. We show that MER...

A problem to account for the direct electron-positron annihilation in positron-hydrogen scattering above the positronium formation threshold has been resolved within the time independent formalism. The generalization of the optical theorem is derived for the case when an absorption potential is present in the Hamiltonian. With this theorem the annihilation cross section is fully determined by s...

In this work we study electronic properties of quantum dots relevant to Compton scattering and positron annihilation. The system is modeled by an electron gas confined by a spherical potential of given radius and depth. Electron-electron correlations are not considered in this study. We find that the broadening of the electronic momentum density around a suitably defined Fermi momentum scales w...

Experiments on electronic excitation of molecules using positron as incident particle have shown much larger cross sections than in the electron scattering case. The comprehension these inelastic processes represent a great challenge and only few studies are discussed literature. For example, for C6H6 molecule experimental theoretical calculations not very advanced state same case (Benzene simp...