From JLab via DOE Pulse: “Quarks’ spins dictate their location in the proton”


Jefferson Lab

“A successful measurement of the distribution of quarks that make up protons conducted at DOE’s Jefferson Lab has found that a quark’s spin can predict its general location inside the proton. Quarks with spin pointed in the up direction will congregate in the left half of the proton, while down-spinning quarks hang out on the right. The research also confirms that scientists are on track to the first-ever three-dimensional inside view of the proton.

The quark structure of the proton. (The color assignment of individual quarks is not important, only that all three colors are present.)

The proton lies at the heart of every atom that builds our visible universe, yet scientists are still struggling to obtain a detailed picture of how it is composed of its primary building blocks: quarks and gluons. Too small to see with ordinary microscopes, protons and their quarks and gluons are instead illuminated by particle accelerators. At Jefferson Lab, the CEBAF accelerator directs a stream of electrons into protons, and huge detectors then collect information about how the particles interact.


According to Harut Avakian, a Jefferson Lab staff scientist, these observations have so far revealed important basic information on the proton’s structure, such as the number of quarks and their momentum distribution. This information comes from scattering experiments that detect only whether a quark was hit but do not measure the particles produced from interacting quarks.

‘If you sum the momenta of those quarks, it can be compared to the momentum of the proton. What scientists were doing these last 40 years, they were investigating the momentum distribution of quarks along the direction in which the electron looks at it – a one-dimensional picture of the proton,’ he explains.

Now, he and his colleagues have used a new experimental method that can potentially produce a full three-dimensional view of the proton.”

See the full article here.

DOE Pulse highlights work being done at the Department of Energy’s national laboratories. DOE’s laboratories house world-class facilities where more than 30,000 scientists and engineers perform cutting-edge research spanning DOE’s science, energy, National security and environmental quality missions. DOE Pulse is distributed twice each month.

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