Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Spinning electrons yield positrons for research

02.06.2016

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) at the Department of Energy's Jefferson Lab, a team of researchers has, for the first time, demonstrated a new technique for producing polarized positrons. The method could enable new research in advanced materials and offers a new avenue for producing polarized positron beams for a proposed International Linear Collider and an envisioned Electron-Ion Collider.


The Polarized Electrons for Polarized Positrons (PEPPo) experiment in Jefferson Lab's CEBAF injector demonstrated a new technique for production of polarized positrons. When an energetic electron beam strikes matter, it produces photons that can further convert their energy in pairs of an electron and a positron. If the electron beam is polarized, the polarization can be passed on to the new electrons and positrons.

Credit: DOE's Jefferson Lab

Jefferson Lab Injector Scientist Joe Grames says the idea for the method grew out of the many advances that have been made in understanding and controlling the electron beams used for research in CEBAF.

"We have a lot of experience here at Jefferson Lab in operating a world-leading electron accelerator," Grames said. "We are constantly improving the electron beam for the experiments, pushing the limits of what we can get the electrons to do."

The CEBAF accelerator gathers up free electrons, sets the electrons to spinning like tops, packs them full of additional energy ("accelerating" the particles to up to 12 billion electron-volts), and directs them along a tightly controlled path into experimental targets. Grames and his colleagues would like to take that finesse a step further and transform CEBAF's well-controlled polarized electron beams into well-controlled beams of polarized positrons to offer researchers at Jefferson Lab an additional probe of nuclear matter. They named the endeavor the Polarized Electrons for Polarized Positrons experiment, or PEPPo.

Positrons are the anti-particles of electrons. Where the electron has a negative charge, the positron has a positive one. Producing positrons that are spinning in the same direction, like the electrons in CEBAF, is very challenging. Before PEPPo, researchers had successfully managed to coax polarized positrons into existence using very high-energy electron beams and sophisticated technologies. The PEPPo method, however, puts a new twist on things.

"From the beginning, our aim was to show that we could use the polarized electron beam we produce every day at CEBAF to create the positrons. But we wanted to do that using a low-energy and small-footprint electron beam, so that a university or company may also benefit from our proof of principle," Grames explained.

The PEPPo system was placed inside the CEBAF accelerator's injector, which is the part of the accelerator that generates electrons. The system consists mainly of small magnets for managing the particle beams, targets for transforming them, and detectors for measuring the particles.

In it, a new beam of electrons from CEBAF is directed into a slice of tungsten. The electrons rapidly decelerate as they pass through the tungsten atoms, giving off gamma rays. These gamma rays then interact with other atoms in the tungsten target to produce lower-energy pairs of positrons and electrons. Throughout the process, the polarization of the original electron beam is passed along. The researchers use a magnet to siphon the positrons away from the other particles and direct them into a detector system that measures their energy and polarization.

"We showed that there's a very efficient transfer of polarization from electrons to the positrons," said Grames.

Further, the researchers found that it is also possible to dial up the degree of polarization that they are interested in by selecting positrons of the right energy. While the more abundant lower-energy positrons are less polarized, the positrons with highest-energy retain nearly all of the polarization of the original electron beam. In PEPPo, the electron beam was 85 percent polarized and accelerated to 8 million electron-volts (MeV).

"Nuclear physicists typically want the highest polarization possible for their experiments," he explained. "Positrons collected at half the original electron energy were about 50 percent polarized, which is still quite high. But, as we approached the maximum energy, we measured 82 percent, showing that a very large portion of the original electron polarization is transferred."

The PEPPo experiment ran for four weeks in the spring of 2012. The result has just been published in Physical Review Letters, and it is featured as an Editors' Suggestion.

Grames and his colleagues say now that they have their proof of principle, they want to design a source that is capable of producing a beam of polarized positrons for research.

"With this result in hand, we are now asking ourselves what's the best way to collect these positrons into a beam that may be used by nuclear physicists in experiments at Jefferson Lab and that may be useful for other facilities. That's the next step."

###

This work was supported in part by the U.S. Department of Energy's Office of Science, the French Centre National de la Recherche Scientifique, and the International Linear Collider project.

Jefferson Science Associates, LLC, a joint venture of the Southeastern Universities Research Association, Inc. and PAE Applied Technologies, manages and operates the Thomas Jefferson National Accelerator Facility, or Jefferson Lab, for the U.S. Department of Energy's Office of Science.

DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov.

Media Contact

Kandice Carter
kcarter@jlab.org
757-269-7263

 @Jblab

http://www.jlab.org 

Kandice Carter | EurekAlert!

Further reports about: Accelerator Electrons Polarized electron beams gamma rays polarization positrons

More articles from Physics and Astronomy:

nachricht Shape matters when light meets atom
05.12.2016 | Centre for Quantum Technologies at the National University of Singapore

nachricht Climate cycles may explain how running water carved Mars' surface features
02.12.2016 | Penn State

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

IHP presents the fastest silicon-based transistor in the world

05.12.2016 | Power and Electrical Engineering

InLight study: insights into chemical processes using light

05.12.2016 | Materials Sciences

High-precision magnetic field sensing

05.12.2016 | Power and Electrical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>