Nuclear Physics (1986) / Chapter Skim
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8 Changing Descriptions of Nuclear Matter
8 Changing Descriptions of Nuclear Matter
Pages 150-159
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From page 150... ...
An improved description of nuclear matter would represent a critical advance in addressing one of the most difficult and important questions in physics: how does nature build stable structures from smaller, more elementary building blocks? We now understand that the most elementary building blocks of nuclei are quarks and gluons.
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From page 151... ...
It is thus important to extend current studies of nuclear reactions that produce such unusual conditions even when the experiments are not directly sensitive to the presence of particles other than nucleons in the nucleus. QUARKS IN NUCLEI The most fundamental building blocks of atomic nuclei, the quarks, interact with each other via the exchange of gluons, thereby creating mesons, baryons, and, ultimately, nuclei.
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From page 152... ...
Experiments of this sort require electron beams of high energy to transfer the requisite momentum to the target nucleus and high duty factor for clean and efficient identification of events in time coincidence; they are thus ideally suited for CEBAF. Additional quark aspects of the strong interaction can be probed by studying other selected features of it.
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From page 153... ...
The normally occurring hadrons fall into two classes: the baryons and the mesons, consisting, respectively, of three quarks and of a quarkantiquark pair confined inside a bag. Quark models, however, also predict the existence of more exotic combinations, for example, six-quark bags, which do not for reasons related to the distribution of quark colors inside the bag readily separate into two normal baryons.
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From page 154... ...
Intense beams of kaons can also be very useful in the study of dibaryons, because they permit systems with one or even two strange quarks to be formed. One of the most exciting predictions of the bag models of hadrons is the existence of a stable, doubly strange dibaryon called the H particle, with a predicted mass around 2.15 GeV.
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From page 155... ...
These studies are expected to reveal much about the quark structure of the nucleus, the nature of the nucleon-nucleon interaction at short distances, and the ways in which the motions of several nucleons might be correlated in the nuclear environment. Using selective reactions to probe and identify correlations will help us understand the degree to which certain states of nuclear excitation can be characterized as nuclear molecules or as relatively unexcited clusters of nucleons, rather than as a nucleon gas in which all the particles move rapidly and independently of one another.
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From page 156... ...
NUCLEAR PROPERTIES UNDER EXTREME CONDITIONS Nuclear spectroscopic measurements using elastic and inelastic scattering reactions as well as a variety of single-particle and multiparticle transfer reactions to study the properties of nuclear energy levels and their decays have provided most of our knowledge about the behavior of nuclear systems. While some nuclear physicists are trying to understand the roles of mesons and quarks in nuclei, others are pursuing the study of the properties of nuclear levels (nuclear wave functions)
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From page 157... ...
Under such conditions, we hope to investigate such phenomena as nuclear shock waves, compression of nuclear material, and the complete disintegration of a nucleus into lighter fragments or even its constituent nucleons. Nuclear properties are expected to change drastically in this region, from the fluidlike cooperative behavior of many nucleons at very low energies to a succession of many individual nucleon-nucleon collisions at high energies.
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From page 158... ...
. The diagram at the bottom identifies some of the charged particles produced in the collision.
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From page 159... ...
Several different approaches are currently being studied for producing such beams, which promise to open up completely new areas of nuclear spectroscopy.
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