Symmetry permeates nature and is fundamental to all laws of physics. One example is parity (mirror) symmetry, which implies that flipping left and right does not change the laws of physics. Laws for electromagnetism, gravity and the subatomic strong force respect parity symmetry, but the subatomic weak force does not.
Precision measurements of parity violation in electron scattering requires the use of high-intensity, polarized electron beams produced at world-class facilities such as the Thomas Jefferson National Accelerator Facility (Jefferson Laboratory).
In this project, we measured parity violation in a kinematic regime where electrons scatter directly off quarks in a nuclear target. Our results allowed a precision test of the Standard Model of particle physics, set a new energy limit for possible interactions beyond the Standard Model, and provided for the first time direct evidence that first generation quarks (up quarks and down quarks) violate parity symmetry in neutral weak interactions.
Xiaochao Zheng is a professor in experimental nuclear and particle physics in the Department of Physics at the University of Virginia.
The Early Career Award program provides financial support that is foundational to young scientists, freeing them to focus on executing their research goals. The development of outstanding scientists early in their careers is of paramount importance to the Department of Energy Office of Science. By investing in the next generation of researchers, the Office of Science champions lifelong careers in discovery science.
For more information, please go to the Early Career Research Program page.
Measurement of Parity Violation in Deep Inelastic Scattering and Studies of the Nucleon Spin Structure at Jlab 6 and 11 GeV
This project will focus on two thrusts of nuclear science: a test of the Standard Model using measurements of the parity‐violating asymmetry in deep inelastic scattering (PVDIS) of polarized electrons on deuterium; and the study of spin observables to address the structure of the nucleon. The project will conduct an exploratory PVDIS experiment using the 6 GeV electron beam at the Jefferson Laboratory that will provide the first precision data on selected coupling constants of the Standard Model. In addition, the project will develop a new large acceptance spectrometer called SoLID to be used with 11 GeV electron beams available by 2015 for both the PVDIS experiments and the study of the spin observables.
The Jefferson Lab PVDIS Collaboration, “Measurement of parity violation in electron-quark scattering.” Nature 506, 67 (2014). [DOI: 10.1038/nature12964]
D. Wang, K. Pan, R.R. Subedi, and X. Deng, “Measurements of the parity-violating asymmetries in electron-deuteron scattering in the nucleon resonance region.” PhysReviewLett 111, 082501 (2013). [DOI: 10.1103/PhysRevLett.111.082501]
D. Wang et al. (The PVDIS Collaboration), “Measurement of parity-violating asymmetry in electron-deuteron inelastic scattering.” Phys. Rev. C 91, 045506 (2015). [DOI: 10.1103/PhysRevC.91.045506]
Additional profiles of the 2010 Early Career Award winners can be found at https://www.energy.gov/science/listings/early-career-program.
The 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, please visit www.energy.gov/science.
Sandra Allen McLean is a Communications Specialist in the Office of Science, sandra.mclean@science.doe.gov.