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From page 128... ... 128 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS 128 6 Symmetry Tests in Nuclear Physics INTRODUCTION: PRIORITIES AND CHALLENGES The realization that symmetries are the key to understanding and classifying the structure of matter and the fundamental forces is among the deepest theoretical insights of this century. The seminal work is identified with the Nobel Prizewinning nuclear theorist, Eugene Wigner, whose ideas have influenced every area of modern physics. Read the entire page →
From page 129... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 129 low energies. There are a number of challenging questions for nuclear physicists at the particle physics boundary: • Do neutrinos have mass? Read the entire page →
From page 130... ... 130 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS modern Standard Model. QED is the theoretical prototype of the entire Standard Model. Read the entire page →
From page 131... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 131 succeeded in isolating a quark. While it is believed that quark confinement is fully consistent with the Standard Model, a rigorous theoretical demonstration has not been made because of the complications of dealing with a nonlinear theory. Read the entire page →
From page 132... ... 132 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS The Standard Model has already stood up against decades of intense experimental scrutiny. Why, then, is it not regarded as the best possible theory of nature, "the ultimate theory"? Read the entire page →
From page 133... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 133 pendence and charge symmetry. Neutrons, being neutral particles, are not affected much by the electromagnetic force. Read the entire page →
From page 134... ... 134 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS particles) and reversal of time (the process evolving in reverse) Read the entire page →
From page 135... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 135 FIGURE 6.3 Schematic diagram of the principle of the first experiment to discover that reflection symmetry is violated by the weak interaction. A 60Co nucleus has many of the properties of a spinning top. Read the entire page →
From page 136... ... 136 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS hundred GeV compared to the 90-GeV W and Z particles of the Standard Model. Currently, the limits from low-energy experiments are often beyond those from direct searches at high-energy accelerators. Read the entire page →
From page 137... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 137 FIGURE 6.4 Schematic diagram of the experiment to search for a neutron electric-dipole moment at the Laue-Langevin Institute (ILL) in Grenoble, France. Read the entire page →
From page 138... ... 138 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS FIGURE 6.5 An experiment to study how well time-reversal symmetry is obeyed in the beta decay of the free neutron. A beam of cold neutrons enters the detector region form the upper right. Read the entire page →
From page 139... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 139 For reasons still unknown, the weak interaction mixes quarks together (in the sense of quantum mechanics) in peculiar ways. Read the entire page →
From page 140... ... 140 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS One of the best ways to measure the mixing between the weak and electromagnetic interactions, the Weinberg angle, is to study the parity-violating interaction between electrons and the nuclei of particular atoms. Parity mixing has been seen in several atomic systems; the best measurement at present is done with 133Cs atoms. Read the entire page →
From page 141... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 141 THE SEARCH FOR NEUTRINO MASS Nuclear physics played a key role in establishing the existence of the mysterious neutrino that was originally proposed to explain the apparent lack of energy conservation in nuclear beta decay. Unique among all the elementary constituents of the Standard Model, the neutrino interacts exclusively by the weak interaction, making its direct detection extremely difficult. Read the entire page →
From page 142... ... 142 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS FIGURE 6.7 A large beta spectrometer (7 feet in diameter) designed especially to measure the energies of electrons emitted from the beta decay of radioactive tritium, an isotope of hydrogen with two neutrons and one proton. Read the entire page →
From page 143... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 143 and reactors. Other important experiments use natural sources of neutrinos either from the Sun or from the collisions of cosmic-ray particles in the upper atmosphere. Read the entire page →
From page 144... ... 144 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS FI G U RE 6 .8 T he in te rio r o f a la rg e ne ut rin o de te ct or u se d at L A M PF to st ud y w he th er o r n ot n eu tri no o sc ill at io ns o cc ur . Read the entire page →
From page 145... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 145 time, several large underground detectors indicated that the ratio of muon- and electron-type neutrinos detected underground was inconsistent with expectations based on a seemingly reliable estimate. The SuperKamiokande experiment has dramatically demonstrated that the anomaly can be traced to a difference in the number of upward going and downward going muon-type neutrinos that are detected. Read the entire page →
From page 146... ... 146 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS been tremendous progress in this field. There are now numerous observations in different systems. Read the entire page →
From page 147... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 147 spallation sources, parity-mixing effects as large as several percent have been observed. Analyzing the observed effects in nuclei is an example of the interplay between nuclear structure and the fundamental interactions. Read the entire page →
From page 148... ... 148 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS years ago as a consequence of a new symmetry introduced to explain the observed CP symmetry of the strong interaction. As first proposed, the axion would decay to two photons or positron-electron pairs. Read the entire page →
From page 149... ... SYMMETRY TESTS IN NUCLEAR PHYSICS 149 accelerators at national laboratories and universities, small tandem accelerators, and cyclotrons. Access to small facilities with specific capabilities for particular experiments is also an important priority for this subfield. Read the entire page →

From page 128...

... 128 NUCLEAR PHYSICS: THE CORE OF MATTER, THE FUEL OF STARS 128 6 Symmetry Tests in Nuclear Physics INTRODUCTION: PRIORITIES AND CHALLENGES The realization that symmetries are the key to understanding and classifying the structure of matter and the fundamental forces is among the deepest theoretical insights of this century. The seminal work is identified with the Nobel Prizewinning nuclear theorist, Eugene Wigner, whose ideas have influenced every area of modern physics.