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

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 pairs 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 distributionsmore » of nucleons bound in nuclei (the EMC effect). They are also relevant for the interpretation of neutrino-oscillation measurements and understanding of neutron-rich systems such as neutron stars.« less

Authors:

Duer, Mike ^[1]

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+ Show Author Affiliations

1. Tel Aviv Univ., Ramat Aviv (Israel). et al.

Publication Date:

Mon Aug 13 00:00:00 EDT 2018

Research Org.:

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 Org.:

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 Org.:

The CLAS Collaboration

OSTI Identifier:

1468654

Alternate Identifier(s):

OSTI ID: 1471087; OSTI ID: 1494138; OSTI ID: 1830326

Report Number(s):

JLAB-PHY-18-2785; DOE/OR/23177-4536
Journal ID: ISSN 0028-0836; PII: 400

Grant/Contract Number:  

SC0016583; AC05-06OR23177; FG02-07ER41528; AC02-06CH11357; AC02-05CH11231

Resource Type:

Accepted Manuscript

Journal Name:

Nature (London)

Additional Journal Information:

Journal Name: Nature (London); Journal Volume: 560; Journal Issue: 7720; Journal ID: ISSN 0028-0836

Publisher:

Nature Publishing Group

Country of Publication:

United States

Language:

English

Subject:

73 NUCLEAR PHYSICS AND RADIATION PHYSICS