Quarks and gluons in hadrons and nuclei Page: 5 of 31
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have enhanced masses relative to their low-J counterparts due to "one gluon ex-
change"; thus the x(1230) resonance, with J = 3/2, has greater mass than the J =
Now move up a layer in complexity to the world of molecules (QED) and nuclei
At the risk of being accused of oversimplification by the atomic experts, I
will divide the interatomic forces into three broad classes, then make analogy in
the QCD world with interhadronic forces at the level of the quarks and gluons.
Covalent van der Waals Ioni,.
Atoms e exchange "two photon" Na+CI-
Hadrons quark exchange "two gluon" no analogue if
Nuclei color confined in
If this was the whole story, then nuclear physics from QCD would be a rerun
of molecules from QED. However, confinement of color breaks the simple analogy.
The quark exchange at large distances (> 1 fm) is contained within the confined
packages, dominantly pions. The confinement of gluons in glueballs also breaks
the analogy with van der Waals' forces. The hope that QCD would predict observa-
ble color van der Waals' forces in nuclei is most probably flawed, as the gluons
will be confined within colorless glueballs. Computer simulations of QCD suggest
that the lightest glueballs have masses in excess of 1 GeV and so transmit forces
over much less than a nucleon radius. Thus their presence is hidden in nuclear
It is an open question whether analogues of ionic forces occur in dense or
hot nuclear systems; whether multiquark clusters occur within nuclei; whether
quark-gluon plasma may form in hot-dense systems.
If color attractions among quarks are the source of internucleon forces, then
there could exist analogous clusters of mesons - "meson molecules". The instabil-
ity of most mesons prevents formation of these systems, but a, K, r are stable on
the time scales of the strong interactions and may have the chance to bind.
Indeed Weinstein and Isgur find that such attractions occur in S-wave. The nn
system has a strong enhancement above 2m which may be manifested in the j, win
dipion spectrum. The KK system binds forming nearly degenerate I = 0, 1 systems
10 MeV below 2mK. The S*(975 MeV) and 6(980 MeV), scalar "mesons", thus appear to
be meson nlecules; meson analogues of the 1=0 deuteron (whose I=1 partner is
above 2rN) .
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Close, F. E. Quarks and gluons in hadrons and nuclei, article, December 1, 1989; Tennessee. (https://digital.library.unt.edu/ark:/67531/metadc1058782/m1/5/: accessed March 21, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.