Modified structure of protons and neutrons in correlated pairs

The CLAS Collaboration

Research output: Contribution to journalLetter

7 Citations (Scopus)

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 cause 1–3 . Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei 4,5 . 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.

Original languageEnglish (US)
Pages (from-to)354-358
Number of pages5
JournalNature
Volume566
Issue number7744
DOIs
StatePublished - Feb 21 2019

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Neutrons
Protons
Nuclear Physics
Nucleons

All Science Journal Classification (ASJC) codes

  • General

Cite this

The CLAS Collaboration. / Modified structure of protons and neutrons in correlated pairs. In: Nature. 2019 ; Vol. 566, No. 7744. pp. 354-358.
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title = "Modified structure of protons and neutrons in correlated pairs",
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 cause 1–3 . Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei 4,5 . 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.",
author = "{The CLAS Collaboration} and B. Schmookler and M. Duer and A. Schmidt and O. Hen and S. Gilad and E. Piasetzky and M. Strikman and Weinstein, {L. B.} and S. Adhikari and M. Amaryan and A. Ashkenazi and Mark Strikman and J. Ball and I. Balossino and L. Barion and M. Bashkanov and M. Battaglieri and A. Beck and I. Bedlinskiy and Biselli, {A. S.} and S. Boiarinov and Briscoe, {W. J.} and Brooks, {W. K.} and Burkert, {V. D.} and Carman, {D. S.} and A. Celentano and G. Charles and T. Chetry and G. Ciullo and E. Cohen and Cole, {P. L.} and V. Crede and R. Cruz-Torres and A. D’Angelo and N. Dashyan and {De Sanctis}, E. and {De Vita}, R. and A. Deur and S. Diehl and C. Djalali and R. Dupre and H. Egiyan and {El Fassi}, L. and L. Elouadrhiri and P. Eugenio and G. Fedotov and R. Fersch and A. Filippi and Forest, {T. A.} and G. Gavalian",
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Modified structure of protons and neutrons in correlated pairs. / The CLAS Collaboration.

In: Nature, Vol. 566, No. 7744, 21.02.2019, p. 354-358.

Research output: Contribution to journalLetter

TY - JOUR

T1 - Modified structure of protons and neutrons in correlated pairs

AU - The CLAS Collaboration

AU - Schmookler, B.

AU - Duer, M.

AU - Schmidt, A.

AU - Hen, O.

AU - Gilad, S.

AU - Piasetzky, E.

AU - Strikman, M.

AU - Weinstein, L. B.

AU - Adhikari, S.

AU - Amaryan, M.

AU - Ashkenazi, A.

AU - Strikman, Mark

AU - Ball, J.

AU - Balossino, I.

AU - Barion, L.

AU - Bashkanov, M.

AU - Battaglieri, M.

AU - Beck, A.

AU - Bedlinskiy, I.

AU - Biselli, A. S.

AU - Boiarinov, S.

AU - Briscoe, W. J.

AU - Brooks, W. K.

AU - Burkert, V. D.

AU - Carman, D. S.

AU - Celentano, A.

AU - Charles, G.

AU - Chetry, T.

AU - Ciullo, G.

AU - Cohen, E.

AU - Cole, P. L.

AU - Crede, V.

AU - Cruz-Torres, R.

AU - D’Angelo, A.

AU - Dashyan, N.

AU - De Sanctis, E.

AU - De Vita, R.

AU - Deur, A.

AU - Diehl, S.

AU - Djalali, C.

AU - Dupre, R.

AU - Egiyan, H.

AU - El Fassi, L.

AU - Elouadrhiri, L.

AU - Eugenio, P.

AU - Fedotov, G.

AU - Fersch, R.

AU - Filippi, A.

AU - Forest, T. A.

AU - Gavalian, G.

PY - 2019/2/21

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N2 - 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 cause 1–3 . Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei 4,5 . 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.

AB - 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 cause 1–3 . Recent observations suggest that the EMC effect is related to close-proximity short-range correlated (SRC) nucleon pairs in nuclei 4,5 . 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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U2 - 10.1038/s41586-019-0925-9

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VL - 566

SP - 354

EP - 358

JO - Nature

JF - Nature

SN - 0028-0836

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