5.1: The Nucleon
Understand the structure of the nucleon. Other Information:
Protons and neutrons, collectively called nucleons, are the building blocks of nuclear matter and thus form the heart of every
atom in the universe. But nucleons are themselves composed of quarks bound together by gluons, the carriers of the strong
force. This strong force is responsible for the structure of nucleons and their composite structures, atomic nuclei, as well
as neutron stars. The nucleus is an ideal system to study the strong interaction, which can be described by a strongly coupled
quantum field theory called QCD. To understand nucleon structure, we will pursue several approaches. Probe the mechanism of
quark confinement inside the nucleon. Although protons and neutrons can be separately observed, their quark and gluon constituents
cannot, because they are permanently confined inside the nucleons. While the mechanism of quark confinement is qualitatively
explained by QCD, a quantitative understanding remains one of our great intellectual challenges. Our strategy includes the
following emphases: • Use high-intensity polarized electron beams at the TJNAF to measure properties of the proton, neutron,
and simple nuclei for comparison with theoretical calculations to provide an improved quantitative understanding of their
quark structure. • Use high-energy polarized proton-proton collisions at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven
National Laboratory to determine the proton structure—how the quarks and particularly the gluons, the carriers of the strong
force, assemble themselves to give the proton's properties. • Upgrade TJNAF to provide higher-energy electron and photon beams
to probe quark confinement and nucleon structure in a regime that will allow a more complete determination of the quark properties.
Search for gluon saturation. Recent calculations suggest that, in high-energy collisions, nucleons and nuclei can behave in
a completely new way, as if filled or “saturated” with many gluons. These gluons have remarkable properties, analogous both
to spin glasses and to the Bose-Einstein condensates studied in condensed matter and atomic physics. This gluonic system may
have universal properties, independent of the nucleus in which it resides, whose study could greatly increase our understanding
of the quark-gluon structure of matter at high energy. Our strategy includes the following emphasis: • Explore the development
of an electron-nucleus collider that would allow the gluon saturation of nuclear matter to be seen.
Indicator(s):
|
