Letter | Published:

Probing high-momentum protons and neutrons in neutron-rich nuclei

Naturevolume 560pages617621 (2018) | Download Citation

Abstract

The atomic nucleus is one of the densest and most complex quantum-mechanical systems in nature. Nuclei account for nearly all the mass of the visible Universe. The properties of individual nucleons (protons and neutrons) in nuclei can be probed by scattering a high-energy particle from the nucleus and detecting this particle after it scatters, often also detecting an additional knocked-out proton. Analysis of electron- and proton-scattering experiments suggests that some nucleons in nuclei form close-proximity neutron–proton pairs1,2,3,4,5,6,7,8,9,10,11,12 with high nucleon momentum, greater than the nuclear Fermi momentum. However, how excess neutrons in neutron-rich nuclei form such close-proximity pairs remains unclear. Here we measure protons and, for the first time, neutrons knocked out of medium-to-heavy nuclei by high-energy electrons and show that the fraction of high-momentum protons increases markedly with the neutron excess in the nucleus, whereas the fraction of high-momentum neutrons decreases slightly. This effect is surprising because in the classical nuclear shell model, protons and neutrons obey Fermi statistics, have little correlation and mostly fill independent energy shells. These high-momentum nucleons in neutron-rich nuclei are important for understanding nuclear parton distribution functions (the partial momentum distribution of the constituents of the nucleon) and changes in the quark distributions of nucleons bound in nuclei (the EMC effect)1,13,14. They are also relevant for the interpretation of neutrino-oscillation measurements15 and understanding of neutron-rich systems such as neutron stars3,16.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

  1. 1.

    Hen, O., Miller, G. A., Piasetzky, E. & Weinstein, L. B. Nucleon–nucleon correlations, short-lived excitations, and the quarks within. Rev. Mod. Phys. 89, 045002 (2017).

  2. 2.

    degli Atti, C.C. In-medium short-range dynamics of nucleons: recent theoretical and experimental advances. Phys. Rep. 590, 1–85 (2015).

  3. 3.

    Frankfurt, L., Sargsian, M. & Strikman, M. Recent observation of short-range nucleon correlations in nuclei and their implications for the structure of nuclei and neutron stars. Int. J. Mod. Phys. A 23, 2991–3055 (2008).

  4. 4.

    Subedi, R. et al. Probing cold dense nuclear matter. Science 320, 1476–1478 (2008).

  5. 5.

    CLAS Collaboration. Momentum sharing in imbalanced Fermi systems. Science 346, 614 – 617 (2014).

  6. 6.

    Korover, I. et al. Probing the repulsive core of the nucleon–nucleon interaction via the 4He(e,epN) triple-coincidence reaction. Phys. Rev. Lett. 113, 022501 (2014).

  7. 7.

    Piasetzky, E., Sargsian, M., Frankfurt, L., Strikman, M. & Watson, J. W. Evidence for strong dominance of proton–neutron correlations in nuclei. Phys. Rev. Lett. 97, 162504 (2006).

  8. 8.

    Tang, A. et al. np short-range correlations from (p, 2p + n) measurements. Phys. Rev. Lett. 90, 042301 (2003).

  9. 9.

    Fomin, N. et al., New measurements of high-momentum nucleons and short-range structures in nuclei. Phys. Rev. Lett. 108, 092502 (2012).

  10. 10.

    CLAS Collaboration. Measurement of two- and three-nucleon short-range correlation probabilities in nuclei. Phys. Rev. Lett. 96, 082501 (2006).

  11. 11.

    Frankfurt, L. L., Strikman, M. I., Day, D. B. & Sargsyan, M. Evidence for short-range correlations from high Q 2 (e,e′) reactions. Phys. Rev. C 48, 2451 (1993).

  12. 12.

    Arrington, J., Higinbotham, D.W., Rosner, G. & Sargsian, M. Hard probes of short-range nucleon–nucleon correlations. Prog. Part. Nucl. Phys. 67, 898–938 (2012).

  13. 13.

    Weinstein, L. B., Piasetzky, E., Higinbotham, D. W., Gomez, J., Hen, O. & Shneor, R. Short range correlations and the EMC effect. Phys. Rev. Lett. 106, 052301 (2011).

  14. 14.

    Hen, O., Piasetzky, E. & Weinstein, L.B. New data strengthen the connection between short range correlations and the EMC effect. Phys. Rev. C 85, 047301 (2012).

  15. 15.

    Gallagher, H., Garvey, G. & Zeller, G. P. Neutrino–nucleus interactions. Annu. Rev. Nucl. Part. Sci. 61, 355–378 (2011).

  16. 16.

    Li, B. A., Cai, B. J., Chen, L.W. & Xu, J. Nucleon effective masses in neutron-rich matter. Prog. Part. Nucl. Phys. 99, 29–119 (2018).

  17. 17.

    Caurier, E., Martínez-Pinedo, G., Nowacki, F., Poves, A. & Zuker, A. P. The shell model as a unified view of nuclear structure. Rev. Mod. Phys. 77, 427–488 (2005).

  18. 18.

    Kelly, J. J. Nucleon knockout by intermediate-energy electrons. Adv. Nucl. Phys. 23, 75–294 (1996).

  19. 19.

    Dickhoff, W. H. & Barbieri, C. Self-consistent Green’s function method for nuclei and nuclear matter. Prog. Part. Nucl. Phys. 52, 377–496 (2004).

  20. 20.

    Carlson, J. et al., Quantum Monte Carlo methods for nuclear physics. Rev. Mod. Phys. 87, 1067–1118 (2015).

  21. 21.

    Frankfurt, L. L. & Strikman, M. I. High-energy phenomena, short-range nuclear structure and QCD. Phys. Rep. 76, 215–347 (1981).

  22. 22.

    Bogner, S. K. & Roscher, D. High-momentum tails from low-momentum effective theories. Phys. Rev. C 86, 064304 (2012).

  23. 23.

    More, S. N., Bogner, S. K. & Furnstahl, R. J. Scale dependence of deuteron electrodisintegration. Phys. Rev. C 96, 054004 (2017).

  24. 24.

    Mecking, B. A. et al. The CEBAF large acceptance spectrometer (CLAS). Nucl. Instrum. Methods A 503, 513–553 (2003).

  25. 25.

    Wiringa, R. B., Schiavilla, R., Pieper, S. C. & Carlson, J. Nucleon and nucleon-pair momentum distributions in A≤12 nuclei. Phys. Rev. C 89, 024305 (2014).

  26. 26.

    Sargsian, M.M. New properties of the high-momentum distribution of nucleons in asymmetric nuclei. Phys. Rev. C 89, 034305 (2014).

  27. 27.

    Ryckebusch, J., Vanhalst, M. & Cosyn, W. Stylized features of single-nucleon momentum distributions. J. Phys. G 42, 055104 (2015).

  28. 28.

    Rios, A., Polls, A. & Dickhoff, W. H. Depletion of the nuclear Fermi sea. Phys. Rev. C 79, 064308 (2009).

  29. 29.

    Kortelainen, M. and Suhonen, J. Nuclear matrix elements of 0νββ decay with improved short-range correlations. Phys. Rev. C 76, 024315 (2007).

  30. 30.

    Frankfurt, L. L., Sargsian, M. M. & Strikman, M. I. Feynman graphs and generalized eikonal approach to high energy knock-out processes. Phys. Rev. C 56, 1124 (1997).

  31. 31.

    Colle, C., Cosyn, W. & Ryckebusch, J. Final-state interactions in two-nucleon knockout reactions. Phys. Rev. C 93, 034608 (2016).

  32. 32.

    Colle, C. et al. Extracting the mass dependence and quantum numbers of short-range correlated pairs from A(e,ep) and A(e, epp) scattering. Phys. Rev. C 92, 024604 (2015).

  33. 33.

    Dutta, D., Hafidi, K. & Strikman, M. Color transparency: past, present and future. Prog. Part. Nucl. Phys. 69, 1–27 (2013).

  34. 34.

    CLAS Collaboration. Measurement of transparency ratios for protons from short-range correlated pairs. Phys. Lett. B 722, 63–68 (2013).

  35. 35.

    Shneor, R. et al., Investigation of proton–proton short-range correlations via the 12C(e,epp) reaction. Phys. Rev. Lett. 99, 072501 (2007).

Download references

Acknowledgements

This work was supported by the US Department of Energy (DOE), contract number DEAC05-06OR23177, under which Jefferson Science Associates, LLC, operates the Thomas Jefferson National Accelerator Facility; 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.

Reviewer information

Nature thanks T. Aumann, D. Phillips and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Author information

Author notes

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

Affiliations

  1. Tel Aviv University, Tel Aviv, Israel

    • M. Duer
    • , E. Piasetzky
    • , M. Braverman
    • , E. O. Cohen
    •  & I. Korover
  2. Massachusetts Institute of Technology, Cambridge, MA, USA

    • O. Hen
    • , A. Ashkenazi
    • , A. Beck
    • , R. Cruz-Torres
    • , S. Gilad
    • , G. Laskaris
    • , S. Mey-Tal Beck
    • , M. Patsyuk
    • , A. Papadopoulou
    • , A. Schmidt
    • , B. A. Schmookler
    •  & E. P. Segarra
  3. Universidad Técnica Federico Santa María, Valparaíso, Chile

    • H. Hakobyan
    • , W. K. Brooks
    • , A. El Alaoui
    •  & T. Mineeva
  4. Old Dominion University, Norfolk, VA, USA

    • L. B. Weinstein
    • , M. J. Amaryan
    • , S. Bueltmann
    • , D. Bulumulla
    • , G. Charles
    • , G. Dodge
    • , F. Hauenstein
    • , C. E. Hyde
    • , M. Khachatryan
    • , A. Klein
    • , S. E. Kuhn
    • , S. Nadeeshani
    • , D. Payette
    • , J. Poudel
    • , Y. Prok
    •  & Z. W. Zhao
  5. Thomas Jefferson National Accelerator Facility, Newport News, VA, USA

    • D. Higinbotham
    • , V. Batourine
    • , S. Boiarinov
    • , W. K. Brooks
    • , V. D. Burkert
    • , D. S. Carman
    • , P. L. Cole
    • , A. Deur
    • , H. Egiyan
    • , G. Gavalian
    • , F. X. Girod
    • , L. Guo
    • , N. Harrison
    • , V. Mokeev
    • , P. Nadel-Turonski
    • , E. Pasyuk
    • , K. Park
    • , P. Rossi
    • , Y. G. Sharabian
    • , S. Stepanyan
    • , M. Ungaro
    •  & X. Wei
  6. Mississippi State University, Missisippi State, MS, USA

    • K. P. Adhikari
    • , L. El Fassi
    •  & M. L. Kabir
  7. Florida International University, Miami, FL, USA

    • S. Adhikari
    • , L. Guo
    •  & W. Phelps
  8. Argonne National Laboratory, Argonne, IL, USA

    • J. Arrington
    • , M. Hattawy
    • , K. Hafidi
    • , B. Mustapha
    •  & X. Zheng
  9. IRFU, CEA, Université Paris-Saclay, Gif-sur-Yvette, France

    • J. Ball
    • , M. Defurne
    • , C. Marchand
    • , S. Procureur
    •  & F. Sabatié
  10. INFN, Sezione di Ferrara, Ferrara, Italy

    • I. Balossino
    • , L. Barion
    • , G. Ciullo
    • , M. Contalbrigo
    • , P. Lenisa
    •  & A. Movsisyan
  11. INFN, Sezione di Genova, Genova, Italy

    • M. Battaglieri
    • , A. Celentano
    • , R. De Vita
    • , M. Osipenko
    •  & M. Ripani
  12. Kyungpook National University, Daegu, South Korea

    • V. Batourine
    • , W. Kim
    • , K. Park
    •  & J. A. Tan
  13. Institute of Theoretical and Experimental Physics, Moscow, Russia

    • I. Bedlinskiy
    •  & O. Pogorelko
  14. Fairfield University, Fairfield, CT, USA

    • A. S. Biselli
  15. Carnegie Mellon University, Pittsburgh, PA, USA

    • A. S. Biselli
    •  & R. A. Schumacher
  16. The George Washington University, Washington, DC, USA

    • W. J. Briscoe
    • , Y. Ilieva
    •  & S. Strauch
  17. University of Connecticut, Storrs, CT, USA

    • F. Cao
    • , B. A. Clary
    • , K. Joo
    • , A. Kim
    •  & N. Markov
  18. Ohio University, Athens, OH, USA

    • T. Chetry
    •  & K. Hicks
  19. Università di Ferrara, Ferrara, Italy

    • G. Ciullo
  20. University of Glasgow, Glasgow, UK

    • L. Clark
    • , D. G. Ireland
    • , K. Livingston
    • , I. J. D. MacGregor
    • , B. McKinnon
    • , R. A. Montgomery
    • , D. Protopopescu
    • , G. Rosner
    •  & D. Sokhan
  21. Idaho State University, Pocatello, ID, USA

    • P. L. Cole
    • , O. Cortes
    •  & T. A. Forest
  22. Catholic University of America, Washington, DC, USA

    • P. L. Cole
    •  & F. J. Klein
  23. Florida State University, Tallahassee, FL, USA

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

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

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

    • N. Dashyan
    • , Y. Ghandilyan
    • , G. Khachatryan
    •  & H. Voskanyan
  27. INFN, Laboratori Nazionali di Frascati, Frascati, Italy

    • E. De Sanctis
    • , M. Mirazita
    •  & P. Rossi
  28. University of South Carolina, Columbia, SC, USA

    • C. Djalali
    • , R. W. Gothe
    • , Y. Ilieva
    •  & S. Strauch
  29. Institut de Physique Nucléaire, CNRS/IN2P3 and Université Paris Sud, Orsay, France

    • R. Dupre
    • , C. Munoz-Camacho
    • , S. Niccolai
    •  & E. Voutier
  30. Christopher Newport University, Newport News, VA, USA

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

    • R. Fersch
    •  & K. A. Griffoen
  32. INFN, Sezione di Torino, Torino, Italy

    • A. Filippi
  33. University of New Hampshire, Durham, NH, USA

    • G. Gavalian
    •  & M. Holtrop
  34. University of Richmond, Richmond, VA, USA

    • G. P. Gilfoyle
  35. James Madison University, Harrisonburg, VA, USA

    • K. L. Giovanetti
    •  & G. Niculescu
  36. Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, Moscow, Russia

    • E. Golovatch
    • , B. S. Ishkhanov
    • , E. L. Isupov
    •  & V. Mokeev
  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. Temple University, Philadelphia, PA, USA

    • M. Paolone
    •  & N. Sparveris
  40. California State University, Carson, CA, USA

    • J. W. Price
  41. Edinburgh University, Edinburgh, UK

    • G. D. Smith
    • , D. P. Watts
    •  & N. Zachariou
  42. Università di Genova, Genova, Italy

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

    • M. Ungaro

Consortia

  1. The CLAS Collaboration

Contributions

The CEBAF large acceptance spectrometer was designed and constructed by the CLAS Collaboration and Jefferson Laboratory. Data 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 M. Duer with input from O. Hen, E. Piasetzky and L. B. Weinstein and reviewed by the CLAS Collaboration.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to O. Hen.

Supplementary information

  1. Supplementary Information

    This file contains Supplementary Text and Data, Supplementary Figures 1–31, Supplementary Tables 1–11 and Supplementary References.

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/s41586-018-0400-z

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.