Modified structure of protons and neutrons in correlated pairs

Nature
CLAS Collaboration

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 cause1-3. 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 an...Continue Reading

References

Nov 1, 1993·Physical Review C: Nuclear Physics·L L FrankfurtM Sargsyan
May 1, 1994·Physical Review. D·J GomezR M Lombard-Nelsen
Feb 7, 2003·Physical Review Letters·A TangD Zhalov
Apr 12, 2006·Physical Review Letters·K S EgiyanUNKNOWN CLAS Collaboration
Dec 13, 2006·Physical Review Letters·E PiasetzkyJ W Watson
Oct 13, 2007·Physical Review Letters·R ShneorUNKNOWN Jefferson Lab Hall A Collaboration
May 31, 2008·Science·R SubediL Zhu
Aug 8, 2009·Physical Review Letters·I C CloëtA W Thomas
Mar 17, 2011·Physical Review Letters·L B WeinsteinR Shneor
May 1, 2012·Physical Review Letters·N BaillieUNKNOWN CLAS Collaboration
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Oct 18, 2014·Science·O HenUNKNOWN Jefferson Lab CLAS Collaboration
Jan 13, 2018·Physical Review Letters·Jiunn-Wei ChenAchim Schwenk
Aug 15, 2018·Nature·UNKNOWN CLAS Collaboration

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Citations

Feb 28, 2020·Nature·A SchmidtUNKNOWN The CLAS Collaboration
Feb 23, 2019·Nature·Gerald Feldman
Sep 7, 2019·Physical Review Letters·J Arrington, N Fomin
Mar 24, 2020·Physical Review Letters·E P SegarraO Hen
May 21, 2019·Physical Review Letters·M DuerUNKNOWN CLAS Collaboration
Jan 16, 2021·Physical Review Letters·X G WangW Melnitchouk
Jun 11, 2021·Physical Review Letters·William DetmoldUNKNOWN NPLQCD Collaboration
Nov 8, 2019··Eli Piasetzky, Eli Piasetzky
Nov 8, 2019··Mark Strikman, Mark Strikman

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Methods Mentioned

BETA
CLAS
electron scattering

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