THE NN INTERACTION

Yu. A. SIMONOV
1990 Le Journal de Physique Colloques  
A review of NN interaction models is presented starting from perturbative and nonperturbative qq interactions in QCD. Spin structure of baryons and mesons is compared and mechanism of spinorbit cancellation in excited baryons is explained. Classification of quark and gluon exchanges in NN at high and low energies is given, and the Pomeron structure is elaborated as a two-gluon glueball, by inspecting recently computed glueball Regge-trajectories, The quark potential models of NN interaction
more » ... NN interaction with and without Quark Compound Bag (QCB) are discussed and the quark origin of the short-range NN repulsion is reviewed. The NN spin effects are discussed in meson exchanges, Reggeanalysis and quark potential models. 1. Introduction. Duality, t-channel and S-channel poles. There are nowadays many approximate approaches to the theoretical description of the NN interaction, which one can divide into three groups: i) t-channel and ii) S-channel dynamics iii) combination of t-channel and S-channel. This division has a limited sense. In the first group one has the meson exchange model (MEM) at low (up to 300MeV) energy [l-51, MEM with n production and A channel up to I f 2GeV [6-71, the Regge method at larger energies Tlab 2 3 + 5 GeV [8-101. In the second group one has the first formulation of the QCB model (without ME) [ll], and more generally, the P matrix approach [12]. In a sense, the approaches of these two groups are dual to each other; one can reproduce the NN amplitude as an (infinite) sum over t-channel meson exchanges with however heavy mesons or as a sum over all possible S-channel poles. For practical reasons one should keep only few first terms and then try to compare with experiment. Here one meets with surprises, specific for the NN system. Indeed, for the m system, the t-channel approach immediately fails to reproduce the S-channel p-meson and one needs poles in all three channels, the situation is far from the potential one. In the NN case, however, S-channel poles are of two kinds: the deuteron and its singlet companion are of molecular type are very wide and lie above Tlab =400 MeV [13]. Therefore the first approach i) is adequate at small energy, say Tlab <400 MeV where MEM works pretty well [l-51 and at large energy, Tlab >3GeV, where Regge theory is applicable because all S-channel resonances overlap and the most important physical phenomenon is smooth inelasticity. "'permanent address: ITEP, Moscow 117259, USSR Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1990601 C6-6 COLLOQUE DE PHYSIQUE The second approach, ii) e.g. the original QCB formulation [U], takes into account explicitly the 6q states and is adequate in the gap 20MeV< TIab <l-3 GeV. However to make quantitative description of NN data in the region 0 5 Tlab <l-3 GeV one needs to include both t-channel MEM and S-channel 6q poles. That was successfully done in the full version of the QCB model by several groups : ITEP [14] , Amsterdam [l51 and recently in the related approach by the Argonne gro'up 1161. By now we have definite evidence that MEM even with A channels and ?r production cannot reproduce NN data, e.g. polarized cross sections at energies above 1 GeV [17]. It is also clear of course that MEM cannot reproduce dibaryonic resonances, since the latter are 6q states occurring due to the qq dynamics. In a similar fashion the quark potential model (QPM) developed, combining both perturbative qq interaction and meson exchanges (see [18, 191 for a review). In the present form it is limited to the energies Tlab <400 MeV and is still rather qualitative. 2. At the one-hadron level the PQCD and NPQCD qq (qq) forces provide reasonable explanation
doi:10.1051/jphyscol:1990601 fatcat:wfsl52fy6jhbpnd35hfdry6mma