Positron Annihilation Lifetime Spectroscopy (PALS) is a unique and non-destructive method for characterizing atomistic defects in a wide range of materials. The use of positron beams for PALS offers significant advantages, such as the ability to probe thin layers, multilayers, and to obtain lifetime spectra with the highest quality.
The generation of positron beams for PALS experiments...
Attempts to utilize positronium (Ps)—a hydrogen-like bound state of an electron and a positron—as an energy-tunable beam have been ongoing since the 1980s. To achieve this, a technique was developed whereby a slow positron beam is injected into a dilute gas, where charge exchange generates a Ps beam [1]. Ps beams generated in this manner have been utilized for experiments involving specular...
Positronium is a Hydrogen-like bound state of an electron and positron, and is an eigenstate of both Charge and Parity transformations. Spin-1 ortho-positronium primarily decays to three photons. Observation of a parity violating angular correlation among the decay products would be a clean indication of combined CP-violation, that cannot be mimicked by final state interactions. We present an...
We describe a compact upgrade to the LERF at Jefferson Lab that enables a monochromatic, slow-positron beam (few-eV) with projected intensity >10¹⁰ e⁺/s and ~10⁴× higher brightness than existing facilities, within the capabilities of the current LERF accelerator. The concept uses an electron beam up to 120 MeV incident on a rotating gamma converter, able to absorb 30 kW of linac power. A key...
The search proposed here uses a missing mass method in one photon final state for a reaction of a positron-electron annihilation.Muon and electron g-2 measurements are the only other comparable approaches which are able to give a model independent constraint on the electron-axion (A’) coupling constant.The proposed experiment with a 100 MeV beam in 30-days run will reach a sensitivity for the...
At the Slow Positron Facility (SPF) of the Institute of Materials Structure Science, KEK, high-intensity slow-positron beams are generated from accelerated electrons provided by a normal-conducting S-band linac (50 MeV, up to 900 W) and are supplied for the facility’s peer-reviewed user proposals [1]. In the long-pulse mode (pulse width 1.2 $\mu$s, repetition up to 50 Hz), a beam intensity of...
Positron annihilation spectroscopy (PAS) is a powerful, non-destructive method in modern materials science. Slow mono-energetic positron beams with variable energy enable depth-resolved characterization of atomistic open-volumes in solids. Positrons are highly sensitive to lattice defects, since they can be trapped at vacancies or vacancy clusters, resulting in a change of their lifetimes and...
The 100-year old theory proposed by E. Fermi and further developed by Weizsaker and Williams can be tested by using Compton scattering of quasi-real photons from atomic electrons.Currently known tests have a few percent accuracy which could be improved by at least a factor of 10. The proposed experiment will use an H(e, e_1 + e_2 + \gamma) reaction with selection of the events with the...
In this talk a QED-based analog of the Sivers effect in QCD will be presented. In particular, Compton scattering off an ionized Helium-4 target is used as a process to access the Sivers effect for the electron in the atomic target.
To account for the motion of the bound electron in the Helium target, hydrogen-like wave functions in momentum space are employed.
Both the unpolarized TMD...
