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Register a new userPhoto and Electrodisintegration of Few Body Systems Revisited
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J.-M. Laget
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Twenty years after P. Sauer released the state of the art Faddeev solution of the bound state three nucleon systems, I revisit photo and electrodisengration of few body systems with a special emphasis on the prospects opened at Jefferson Laboratory.
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Recent studies of the electro-disintegration of the few body systems at JLab have revived the field. Not only recoil momentum distributions have been determined in a single shot. But also they confirm that the diagrammatic approach, which I developed 25 years ago, is relevant to analyze them, provided that the Nucleon-Nucleon scattering amplitude, determined in the same energy range, is used. They provide us with a solid starting point to address the issue of the propagation of exotic components of hadrons in nuclear matter
Hadronic composite states are introduced as few-body systems in hadron physics. The $Lambda(1405)$ resonance is a good example of the hadronic few-body systems. It has turned out that $Lambda(1405)$ can be described by hadronic dynamics in a modern technology which incorporates coupled channel unitarity framework and chiral dynamics. The idea of the hadronic $bar KN$ composite state of $Lambda(1405)$ is extended to kaonic few-body states. It is concluded that, due to the fact that $K$ and $N$ have similar interaction nature in s-wave $bar K$ couplings, there are few-body quasibound states with kaons systematically just below the break-up thresholds, like $bar KNN$, $bar KKN$ and $bar KKK$, as well as $Lambda(1405)$ as a $bar KN$ quasibound state and $f_{0}(980)$ and $a_{0}(980)$ as $bar KK$.
A brief review of relativistic effects in few-body systems, of theoretical approaches, recent developments and applications is given. Manifestations of relativistic effects in the binding energies, in the electromagnetic form factors and in three-body observables are demonstrated. The three-body forces of relativistic origin are also discussed.
We present a work which is meant to inspire the few-body practitioners to venture into the study of new, more exotic, systems and to hadron physicists, working mostly on two-body problems, to move in the direction of studying related few-body systems. For this purpose we devote the discussions in the introduction to show how the input two-body amplitudes can be easily obtained using techniques of the chiral unitary theory, or its extensions to the heavy quark sector. We then briefly explain how these amplitudes can be used to solve the Faddeev equations or a simpler version obtained by treating the three-body scattering as that of a particle on a fixed center. Further, we give some examples of the results obtained by studying systems involving mesons. We have also addressed the field of many meson systems, which is currently almost unexplored, but for which we envisage a bright future. Finally, we give a complete list of works dealing with unconventional few-body systems involving one or several mesons, summarizing in this way the findings on the topic, and providing a motivation for those willing to investigate such systems.
Exclusive reactions induced at high momentum transfer in few body systems provide us with an original way to study the production and propagation of hadrons in cold nuclear matter. In very well defined parts of the phase space, the reaction amplitude develops a logarithmic singularity. It is on solid ground since it depends only on on-shell elementary amplitudes and on low momentum components of the nuclear wave function. This is the best window to study the propagation of exotic configurations of hadrons such as, for instance, the onset of color transparency. It may appear earlier in meson photo-production reactions, more particularly in the strange sector, than in more classical quasi elastic scattering of electrons. More generally, those reactions provide us with the best tool to determine the cross section of the scattering of various hadrons (strange particles, vector mesons) from the nucleon and to access the production of possible exotic states.
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