Polarized Partners: Spinning Electrons Yield Spinning Positrons

Researchers demonstrate a new technique for producing polarized positrons that could improve manufacturing and lead to new discoveries.

Electron-positron pairs (e-e+) result when an energetic electron beam strikes matter. If the electron beam is polarized, with most of the electrons spinning in the same direction, that polarization can be passed on to the new electrons and positrons.

The Science

When an energetic electron beam strikes matter, it produces photons, or packets of light, that can further convert their energy into pairs of an electron and a positron, the anti-particle twin to the electron. Researchers demonstrated that if the original electron beam is polarized (electrons “spin” in one direction), this polarization can be transferred to the positrons with nearly 100 percent efficiency.

The Impact

This technique could allow for the exploitation of polarized positron beams for a wide range of applications and research, such as improved product manufacturing and polarized positron beams for the proposed International Linear Collider and Electron-Ion Collider to power breakthrough scientific research.


Researchers use accelerators to coax the electron into performing a wide range of tricks to enable medical tests and treatments, improve product manufacturing, and power breakthrough scientific research. Now, they’re learning how to coax the same tricks out of the electron’s antimatter twin – the positron – to open up a whole new vista of research and applications. Using the Continuous Electron Beam Accelerator Facility (CEBAF), a team of researchers has demonstrated a new technique for producing polarized positrons. The Polarized Electrons for Polarized Positrons (PEPPo) experiment tried a new method using an electron beam source, small magnets to manage the particle beams, targets to transform them, and small detectors to measure the particles. The PEPPo system was installed in the CEBAF accelerator’s injector, the part of the accelerator that generates electrons. In it, a beam of electrons was directed into a slice of tungsten. The electrons rapidly decelerated as they passed through the tungsten atoms, giving off gamma rays. These gamma rays interacted with other atoms in the tungsten target to produce pairs of positrons and electrons. A detector system measured the positrons’ energy and polarization. The researchers showed a very efficient transfer of polarization from the electrons to the positrons. Further, while the more abundant lower-energy positrons were less polarized, the positrons with the highest energy (8 MeV) retained nearly all of the polarization of the original electron beam (85 percent). Further, this technique required far less instrumentation and expensive components than other techniques, and no remnant radioactivity is produced by the process, making it accessible to industry and university labs.


Joe Grames
Thomas Jefferson National Accelerator Facility


This work was supported in part by the U.S. Department of Energy’s (DOE’s) Office of Science, Office of Nuclear Physics, the French Centre National de la Recherche Scientifique, and the International Linear Collider project. The Continuous Electron Beam Accelerator Facility (CEBAF) is a DOE Office of Science user facility.


D. Abbott, et al. (PEPPo Collaboration), “Production of highly polarized positrons using polarized electrons at MeV energies.” Physical Review Letters 116, 214801 (2016). [DOI: 10.1103/PhysRevLett.116.214801]

Related Links

Jefferson Lab: Spinning Electrons Yields Positrons for Research

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