OPPORTUNITIES IN NUCLEAR SCIENCE A Long-Range Plan for ...

THE SCIENCE • PROTONS AND NEUTRONS: STRUCTURE AND INTERACTIONS
Outlook
Recent and planned experimental programs are expanding
our understanding of the structure of the hadrons, the
origins of confinement, and the QCD basis for the NN
interaction. These studies must be carried out over a broad
range of energy and distance scales in order to follow QCD
from the partonic regime characteristic of hard scattering to
the distance scales seen in finite nuclei.
In the short term, the highest priority for this subfield is
to exploit the opportunities available at Jefferson Lab and
with the RHIC spin program. Both of these programs are
poised to make substantial advances, which are threatened
by limited resources to operate the accelerator facilities. The
Facilities Initiative, which has the highest priority in this
long-range plan, is a key component in achieving the goals of
the community. In the medium term, many of the outstanding
scientific opportunities that have been identified in this
chapter require the higher beam energies that will be provided
by the CEBAF 12-GeV Upgrade, which should take place
at the earliest opportunity. In the longer term, an Electron-
Ion Collider has been put forward as the next major facility
for this field. This is an exciting proposal for which the scientific
case will be refined in the next few years. In parallel, it
is essential that the necessary accelerator R&D be pursued
now, to ensure that the optimum technical design is chosen.
Almost every aspect of this subfield is connected in some
way to QCD. The experiments currently under way or
planned are unlikely to lead to breakthroughs in our understanding
of this connection without comparable efforts on
the theoretical front through the development of state-ofthe-art
techniques such as lattice QCD and effective field
theories. These theoretical advances depend in turn on the
major new computational facilities put forward in the
Large-Scale Computing Initiative.
We have seen substantial progress in the past decade, and
experimental and theoretical tools now in place or planned
promise an exciting and enlightening future as we pursue the
quest to understand the nature of strongly interacting matter
in terms of the fundamental building blocks of QCD.
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