Letter | Published:

Measurement of parity violation in electron–quark scattering

Nature volume 506, pages 6770 (06 February 2014) | Download Citation

Abstract

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 not1,2. Historically, parity violation in electron scattering has been important in establishing (and now testing) the standard model of particle physics. One particular set of quantities accessible through measurements of parity-violating electron scattering are the effective weak couplings C2q, sensitive to the quarks’ chirality preference when participating in the weak force, which have been measured directly3,4 only once in the past 40 years. Here we report a measurement of the parity-violating asymmetry in electron–quark scattering, which yields a determination of 2C2u − C2d (where u and d denote up and down quarks, respectively) with a precision increased by a factor of five relative to the earlier result. These results provide evidence with greater than 95 per cent confidence that the C2q couplings are non-zero, as predicted by the electroweak theory. They lead to constraints on new parity-violating interactions beyond the standard model, particularly those due to quark chirality. Whereas contemporary particle physics research is focused on high-energy colliders such as the Large Hadron Collider, our results provide specific chirality information on electroweak theory that is difficult to obtain at high energies. Our measurement is relatively free of ambiguity in its interpretation, and opens the door to even more precise measurements in the future.

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Acknowledgements

We thank the personnel of Jefferson Lab for their efforts which resulted in the successful completion of the experiment, and A. Accardi, P. Blunden, W. Melnitchouk and their collaborators for carrying out the calculations necessary for the completion of the data analysis. X.Z. thanks the Medium Energy Physics Group at the Argonne National Laboratory for support during the initial work on this experiment. J.E. was supported by PAPIIT (DGAPAUNAM) project IN106913 and CONACyT (México) project 151234, and acknowledges the hospitality and support by the Mainz Institute for Theoretical Physics (MITP) where part of his work was completed. This work was supported in part by the Jeffress Memorial Trust (award no. J-836), the US NSF (award no. 0653347), and the US DOE (award nos DE-SC0003885 and DE-AC02-06CH11357). This work was authored by Jefferson Science Associates, LLC under US DOE contract no. DE-AC05-06OR23177. The US Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for US Government purposes.

Author information

Author notes

    • A. Saha

    Deceased.

Affiliations

  1. University of Virginia, Charlottesville, Virginia 22904, USA.

    • D. Wang
    • , R. Subedi
    • , X. Deng
    • , G. D. Cates
    • , M. M. Dalton
    • , C. W. de Jager
    • , D. Jones
    • , N. Liyanage
    • , V. Nelyubin
    • , K. D. Paschke
    • , S. Riordan
    • , K. Saenboonruang
    • , R. Silwal
    • , W. A. Tobias
    •  & X. Zheng
  2. Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

    • K. Pan
    • , W. Bertozzi
    • , W. Deconinck
    • , S. Gilad
    • , J. Huang
    • , S. Kowalski
    • , N. Muangma
    •  & V. Sulkosky
  3. Syracuse University, Syracuse, New York 13244, USA.

    • Z. Ahmed
    • , R. Holmes
    • , C. M. Jen
    • , A. Rakhman
    •  & P. A. Souder
  4. University of Kentucky, Lexington, Kentucky 40506, USA.

    • K. Allada
    •  & C. Dutta
  5. California State University, Los Angeles, Los Angeles, California 90032, USA.

    • K. A. Aniol
    •  & D. J. Margaziotis
  6. College of William and Mary, Williamsburg, Virginia 23187, USA.

    • D. S. Armstrong
    • , J. H. Lee
    •  & B. Zhao
  7. Physics Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.

    • J. Arrington
    • , K. Hafidi
    • , R. J. Holt
    • , P. E. Reimer
    •  & J. Rubin
  8. Istituto Nazionale di Fisica Nucleare, Dipt. di Fisica dell'Univ. di Catania, I-95123 Catania, Italy.

    • V. Bellini
    • , A. Giusa
    • , G. Russo
    •  & C. M. Sutera
  9. Ohio University, Athens, Ohio 45701, USA.

    • R. Beminiwattha
    • , P. M. King
    • , J. H. Lee
    • , J. Roche
    •  & B. Waidyawansa
  10. Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA.

    • J. Benesch
    • , A. Camsonne
    • , J.-P. Chen
    • , E. Chudakov
    • , C. W. de Jager
    • , A. Deur
    • , J.-O. Hansen
    • , D. W. Higinbotham
    • , J. J. LeRose
    • , D. G. Meekins
    • , R. Michaels
    • , S. Nanda
    • , A. Saha
    • , B. Sawatzky
    • , R. Suleiman
    •  & B. Wojtsekhowski
  11. Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.

    • F. Benmokhtar
    • , G. B. Franklin
    • , M. Friend
    • , D. Parno
    •  & B. Quinn
  12. Old Dominion University, Norfolk, Virginia 23529, USA.

    • M. Canan
    • , S. Golge
    •  & C. E. Hyde
  13. INFN, Sezione di Roma, gruppo Sanità and Istituto Superiore di Sanità, I-00161 Rome, Italy.

    • E. Cisbani
    • , S. Frullani
    •  & F. Garibaldi
  14. Università di Bari, I-70126 Bari, Italy.

    • R. De Leo
  15. Rutgers, The State University of New Jersey, Newark, New Jersey 07102, USA.

    • L. El Fassi
  16. Instituto de Física, Universidad Nacional Autónoma de México, 04510 México D.F., Mexico.

    • J. Erler
  17. Temple University, Philadelphia, Pennsylvania 19122, USA.

    • D. Flay
    •  & Z.-E. Meziani
  18. Kharkov Institute of Physics and Technology, Kharkov 61108, Ukraine.

    • A. Glamazdin
  19. Louisiana Technical University, Ruston, Louisiana 71272, USA.

    • K. Grimm
  20. Longwood University, Farmville, Virginia 23909, USA.

    • T. Holmstrom
    •  & K. Rider
  21. Clermont Université, Université Blaise Pascal, CNRS/IN2P3, Laboratoire de Physique Corpusculaire, FR-63000 Clermont-Ferrand, France.

    • C. E. Hyde
  22. Seoul National University, Seoul 151-742, South Korea.

    • Hoyoung Kang
    •  & Y. Oh
  23. University of Massachusetts Amherst, Amherst, Massachusetts 01003, USA.

    • K. S. Kumar
    • , D. McNulty
    •  & L. Mercado
  24. Kent State University, Kent, Ohio 44242, USA.

    • E. Long
  25. INFN, Sezione di Roma and Sapienza — Università di Roma, I-00161 Rome, Italy.

    • F. Meddi
    •  & G. M. Urciuoli
  26. Institut Jožef Stefan, SI-1001 Ljubljana, Slovenia.

    • M. Mihovilovic
    •  & S. Sirca
  27. George Washington University, Washington DC 20052, USA.

    • K. E. Myers
  28. Mississippi State University, Starkeville, Mississippi 39762, USA.

    • A. Narayan
    •  & Nuruzzaman
  29. University of New Hampshire, Durham, New Hampshire 03824, USA.

    • S. K. Phillips
  30. Duke University, Durham, North Carolina 27708, USA.

    • X. Qian
    •  & Y. Qiang
  31. Yerevan Physics Institute, Yerevan 0036, Armenia.

    • A. Shahinyan
  32. China Institute of Atomic Energy, Beijing 102413, China.

    • L. Ye

Consortia

  1. The Jefferson Lab PVDIS Collaboration

Authors

    Contributions

    Authors contributed to one or more of the following areas: proposing, leading, and running the experiment; design, construction, optimization, and testing of the data acquisition system; data analysis; simulation; extraction of the physics results from measured asymmetries; and the writing of this Letter.

    Competing interests

    The author declare no competing financial interests.

    Corresponding author

    Correspondence to X. Zheng.

    J.E. is currently on sabbatical leave at the PRISMA Cluster of Excellence and MITP, Johannes Gutenberg University.

    Supplementary information

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      Supplementary Information

      This file contains Supplementary Methods, Supplementary References and Supplementary Tables 1-2.

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    DOI

    https://doi.org/10.1038/nature12964

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