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

Journal Article · · Nature (London)
 [1]
  1. Tel Aviv Univ., Ramat Aviv (Israel). et al.

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 pairs1-12 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.

Research Organization:
George Washington Univ., Washington, DC (United States); Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States); Mississippi State Univ., Mississippi State, MS (United States); Argonne National Laboratory (ANL), Argonne, IL (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Nuclear Physics (NP); National Science Foundation (NSF); Israel Science Foundation (ISF); Chilean Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT); Commissariat a l’Energie Atomique (CEA); National Research Foundation of Korea (NRF); United Kingdom Science and Technology Facilities Council; Centre National de la Recherche Scientifique (CNRS); Instituto Nazionale di Fisica Nucleare (INFN)
Contributing Organization:
The CLAS Collaboration
Grant/Contract Number:
SC0016583; AC05-06OR23177; FG02-07ER41528; AC02-06CH11357; AC02-05CH11231
OSTI ID:
1468654
Alternate ID(s):
OSTI ID: 1471087; OSTI ID: 1494138; OSTI ID: 1830326
Report Number(s):
JLAB-PHY-18-2785; DOE/OR/23177-4536; PII: 400
Journal Information:
Nature (London), Vol. 560, Issue 7720; ISSN 0028-0836
Publisher:
Nature Publishing GroupCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 95 works
Citation information provided by
Web of Science

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Cited By (7)

Modified structure of protons and neutrons in correlated pairs journal February 2019
Relativistic self-energy decomposition of nuclear symmetry energy and equation of state of neutron matter within QCD sum rules journal August 2019
Isospin composition of the high-momentum fluctuations in nuclei from asymptotic momentum distributions journal November 2019
Proton-proton momentum correlation function as a probe of the high momentum tail of the nucleon-momentum distribution journal January 2020
Towards understanding astrophysical effects of nuclear symmetry energy journal July 2019
Direct Observation of Proton-Neutron Short-Range Correlation Dominance in Heavy Nuclei text January 2018
Relativistic self-energy decomposition of nuclear symmetry energy and equation of state of neutron matter within QCD sum rules text January 2019

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