Quarks and gluons in hadrons and nuclei

In hadron physics we have much data and the hope of confronting them with the fundamental QCD theory of interesting quarks and gluons. This is stimulating but also difficult. A major problem is confinement of colored quarks and gluons within the nucleons - this is simulated on computers where space-time is described as a discrete lattice, but its origins analytically are still rather poorly understood. This confinement phenomenon is also the catch-22 deriving nuclear physics from QCD. In this paper the quarks are confined in nucleons, and so any successful description of the nuclear structure must reduce to that of quarks clustered inside individual nucleons. Thus we have first to understand the proton and neutron - hence the interest in hadron physics. There is the interesting possibility that the interactions and overlaps among closely packed nucleons in large or dense nuclei, or in high-energy collisions of heavy ions, may disturb the distributions of quarks - their spatial or momentum distributions - relative to their behavior when confined in isolated free nucleons. There are indeed hints of such behavior, e.g., the EMC effect where quarks in iron have a slightly different momentum distribution relative to that in the deuteron. Their mean momenta are reduced in iron and other heavy nuclei suggesting greater spatial freedom. Is this liberation a cold precursor to hot deconfinement? Are nucleons in nuclei physically enlarged, or it this a manifestation of quarks exchanged between nucleons, typing the nucleus together and having more spatial mobility than when in a single free nucleon? Future experiments may help to answer these questions -questions raised, in large degree, by the underlying quark theory