Letter | Published:

Modified structure of protons and neutrons in correlated pairs

Naturevolume 566pages354358 (2019) | Download Citation

Abstract

The atomic nucleus is made of protons and neutrons (nucleons), which are themselves composed of quarks and gluons. Understanding how the quark–gluon structure of a nucleon bound in an atomic nucleus is modified by the surrounding nucleons is an outstanding challenge. Although evidence for such modification—known as the EMC effect—was first observed over 35 years ago, there is still no generally accepted explanation for its cause1,2,3. Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei4,5. Here we report simultaneous, high-precision measurements of the EMC effect and SRC abundances. We show that EMC data can be explained by a universal modification of the structure of nucleons in neutron–proton SRC pairs and present a data-driven extraction of the corresponding universal modification function. This implies that in heavier nuclei with many more neutrons than protons, each proton is more likely than each neutron to belong to an SRC pair and hence to have distorted quark structure. This universal modification function will be useful for determining the structure of the free neutron and thereby testing quantum chromodynamics symmetry-breaking mechanisms and may help to discriminate between nuclear physics effects and beyond-the-standard-model effects in neutrino experiments.

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The raw data from this experiment are archived in Jefferson Laboratory’s mass storage silo.

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Acknowledgements

We acknowledge the efforts of the staff of the Accelerator and Physics divisions at Jefferson Laboratory that made this experiment possible. The analysis presented here was carried out as part of the Jefferson Laboratory Hall B Data-Mining project, supported by the US Department of Energy (DOE). The research was also supported by the National Science Foundation, the Israel Science Foundation, the Chilean Comisión Nacional de Investigación Científica y Tecnológica, the French Centre National de la Recherche Scientifique and Commissariat a l’Energie Atomique, the French–American Cultural Exchange, the Italian Istituto Nazionale di Fisica Nucleare, the National Research Foundation of Korea and the UK Science and Technology Facilities Council. The research of M.S. was supported by the US DOE, Office of Science, Office of Nuclear Physics, under award number DE-FG02- 93ER40771. Jefferson Science Associates operates the Thomas Jefferson National Accelerator Facility for the DOE, Office of Science, Office of Nuclear Physics under contract DE-AC05-06OR23177.

Author information

Author notes

  1. A list of authors and their affiliations appears at the end of the paper.

Affiliations

  1. Massachusetts Institute of Technology, Cambridge, MA, USA

    • B. Schmookler
    • , A. Schmidt
    • , O. Hen
    • , S. Gilad
    • , A. Ashkenazi
    • , A. Beck
    • , R. Cruz-Torres
    • , G. Laskaris
    • , S. Mey-Tal Beck
    • , M. Patsyuk
    •  & E. P. Segarra
  2. Tel Aviv University, Tel Aviv, Israel

    • M. Duer
    • , E. Piasetzky
    •  & E. Cohen
  3. Pennsylvania State University, University Park, PA, USA

    • M. Strikman
  4. Old Dominion University, Norfolk, VA, USA

    • L. B. Weinstein
    • , M. Amaryan
    • , G. Charles
    • , F. Hauenstein
    • , C. E. Hyde
    • , M. Khachatryan
    • , A. Klein
    • , S. E. Kuhn
    • , Y. Prok
    •  & Z. W. Zhao
  5. Florida International University, Miami, FL, USA

    • S. Adhikari
    •  & L. Guo
  6. Thomas Jefferson National Accelerator Facility, Newport News, VA, USA

    • H. Avakian
    • , S. Boiarinov
    • , W. K. Brooks
    • , V. D. Burkert
    • , D. S. Carman
    • , A. Deur
    • , H. Egiyan
    • , L. Elouadrhiri
    • , G. Gavalian
    • , F. X. Girod
    • , L. Guo
    • , C. Hanretty
    • , N. Harrison
    • , D. Higinbotham
    • , V. Kubarovsky
    • , V. Mokeev
    • , K. Park
    • , E. Pasyuk
    • , P. Rossi
    • , Y. G. Sharabian
    • , S. Stepanyan
    • , M. Ungaro
    •  & X. Wei
  7. IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France

    • J. Ball
    •  & F. Sabatié
  8. INFN, Sezione di Ferrara, Ferrara, Italy

    • I. Balossino
    • , L. Barion
    • , G. Ciullo
    •  & P. Lenisa
  9. University of York, Heslington, UK

    • M. Bashkanov
    • , D. P. Watts
    •  & N. Zachariou
  10. INFN, Sezione di Genova, Genoa, Italy

    • M. Battaglieri
    • , A. Celentano
    • , R. De Vita
    • , M. Osipenko
    • , M. Ripani
    •  & M. Taiuti
  11. Institute of Theoretical and Experimental Physics, Moscow, Russia

    • I. Bedlinskiy
    • , S. V. Kuleshov
    •  & O. Pogorelko
  12. Fairfield University, Fairfield, CT, USA

    • A. S. Biselli
  13. The George Washington University, Washington, DC, USA

    • W. J. Briscoe
    • , Y. Ilieva
    •  & S. Strauch
  14. Universidad Técnica Federico Santa María, Valparaiso, Chile

    • W. K. Brooks
    • , H. Hakobyan
    • , S. V. Kuleshov
    •  & T. Mineeva
  15. Ohio University, Athens, OH, USA

    • T. Chetry
    • , C. Djalali
    • , G. Fedotov
    •  & K. Hicks
  16. Universitá di Ferrara, Ferrara, Italy

    • G. Ciullo
  17. Lamar University, Beaumont, TX, USA

    • P. L. Cole
  18. Florida State University, Tallahassee, FL, USA

    • V. Crede
    • , P. Eugenio
    •  & A. I. Ostrovidov
  19. INFN, Sezione di Roma Tor Vergata, Rome, Italy

    • A. D’Angelo
    • , L. Lanza
    •  & A. Rizzo
  20. Universitá di Roma Tor Vergata, Rome, Italy

    • A. D’Angelo
    •  & A. Rizzo
  21. Yerevan Physics Institute, Yerevan, Armenia

    • N. Dashyan
    • , H. Hakobyan
    • , G. Khachatryan
    •  & H. Voskanyan
  22. INFN, Laboratori Nazionali di Frascati, Frascati, Italy

    • E. De Sanctis
    • , M. Mirazita
    •  & P. Rossi
  23. University of Connecticut, Storrs, CT, USA

    • S. Diehl
    • , K. Joo
    • , A. Kim
    • , N. Markov
    •  & D. Riser
  24. Institut de Physique Nucléaire, CNRS/IN2P3, Université Paris-Sud, Université Paris-Saclay, Orsay, France

    • R. Dupre
    • , M. Guidal
    • , C. Munoz Camacho
    • , S. Niccolai
    •  & E. Voutier
  25. Mississippi State University, Mississippi State, MS, USA

    • L. El Fassi
    •  & M. L. Kabir
  26. Christopher Newport University, Newport News, VA, USA

    • R. Fersch
  27. College of William and Mary, Williamsburg, VA, USA

    • R. Fersch
    • , K. A. Griffioen
    •  & T. B. Hayward
  28. INFN, Sezione di Torino, Turin, Italy

    • A. Filippi
  29. Idaho State University, Pocatello, ID, USA

    • T. A. Forest
  30. University of Richmond, Richmond, VA, USA

    • G. P. Gilfoyle
  31. Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia

    • E. Golovatch
    • , B. S. Ishkhanov
    • , E. L. Isupov
    • , V. Mokeev
    •  & I. U. Skorodumina
  32. University of South Carolina, Columbia, SC, USA

    • R. W. Gothe
    • , Y. Ilieva
    • , I. U. Skorodumina
    •  & S. Strauch
  33. Argonne National Laboratory, Argonne, IL, USA

    • K. Hafidi
    • , S. Johnston
    • , S. Joosten
    •  & B. Mustapha
  34. University of New Hampshire, Durham, NH, USA

    • M. Holtrop
    •  & R. Paremuzyan
  35. University of Glasgow, Glasgow, UK

    • D. G. Ireland
    • , K. Livingston
    • , I. J. D. MacGregor
    • , B. McKinnon
    • , R. A. Montgomery
    • , D. Protopopescu
    • , G. Rosner
    •  & D. Sokhan
  36. Kyungpook National University, Daegu, Korea

    • H.-S. Jo
    • , W. Kim
    • , K. Park
    •  & J. A. Tan
  37. University of Virginia, Charlottesville, VA, USA

    • D. Keller
    • , Y. Prok
    • , J. Zhang
    •  & X. Zheng
  38. Norfolk State University, Norfolk, VA, USA

    • M. Khandaker
    •  & C. Salgado
  39. Catholic University of America, Washington, DC, USA

    • F. J. Klein
  40. Nuclear Research Centre Negev, Beer-Sheva, Israel

    • I. Korover
  41. Temple University, Philadelphia, PA, USA

    • M. Paolone
    •  & N. Sparveris
  42. Arizona State University, Tempe, AZ, USA

    • E. Pasyuk
  43. California State University, Carson, CA, USA

    • J. W. Price
  44. Carnegie Mellon University, Pittsburgh, PA, USA

    • R. A. Schumacher
  45. Universitá di Genova, Dipartimento di Fisica, Genoa, Italy

    • M. Taiuti
  46. Rensselaer Polytechnic Institute, Troy, NY, USA

    • M. Ungaro
  47. Canisius College, Buffalo, NY, USA

    • M. Wood
  48. Duke University, Durham, NC, USA

    • Z. W. Zhao

Consortia

  1. The CLAS Collaboration

Contributions

CLAS was designed and constructed by the CLAS Collaboration and Jefferson Laboratory. Data acquisition, processing and calibration, Monte Carlo simulations of the detector and data analyses were performed by a large number of CLAS Collaboration members, who also discussed and approved the scientific results. The analysis presented here was performed by B.S. and A.S. with input from S.G., O.H., E. Piasetzky and L.B.W. and reviewed by the CLAS collaboration.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to O. Hen.

Extended data figures and tables

  1. Extended Data Fig. 1 models.

    \({{\boldsymbol{F}}}_{2}^{{\boldsymbol{n}}}\,{\rm{/}}\,{{\boldsymbol{F}}}_{2}^{{\boldsymbol{p}}}\) Ratio of neutron to proton structure functions, \({F}_{2}^{n}\,{\rm{/}}\,{F}_{2}^{p}\), derived from the SRC-driven EMC model (blue band) used in the isoscalar corrections of refs 9 (‘SLAC’, red line) and 10 (‘JLab Hall C’, green line) and derived in the CTEQ-14 global fit, shown here for Q2 = 10 GeV2 (grey band). The large spread among the various models shows the uncertainty in \({F}_{2}^{n}\), a key ingredient in the isoscalar corrections previously applied to the EMC effect data.

  2. Extended Data Table 1 SRC scaling coefficients
  3. Extended Data Table 2 EMC slopes
  4. Extended Data Table 3 Per nucleon, per-proton and per-neutron EMC slopes

Supplementary information

  1. Supplementary Information

    This file contains Supplementary Text and Data, which includes Supplementary Figures 1-4, Supplementary Tables 1-7 and additional references

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DOI

https://doi.org/10.1038/s41586-019-0925-9

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