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3 How Are Matter, Space, and Time Unified?
Pages 43-59

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From page 43...
... The earliest history of the universe is dominated by physics of the highest energies, so that gaining an understanding of it depends on progress in understanding microscopic physics in these extreme domains. Conversely, the universe, unlike accelerators where experiments are limited by available beam lines and interaction regions, is an ever-open laboratory, one that produces a great range of phenomena that span an incredible energy range and that can be used to probe and extend ideas on microphysics.
From page 44...
... Rather than address ongoing and proposed accelerator programs that are reviewed elsewhere by other responsible scientific groups (laboratory program committees, the NRC, and the DOE/NSF High Energy Physics Advisory Panel and the Nuclear Science Advisory Committee) , this committee focuses on identifying additional and complementary opportunities for the use of new techniques and technologies to probe the most fundamental questions at the interface between particle physics and astronomy and astrophysics.
From page 45...
... Furthermore, these experiments allowed limits to be defined on proton decay that already rule out the simplest grand unified theories. Clearly, achieving substantial improvements in experimental sensitivity to proton decay will be important to improving our understanding of the early universe.
From page 46...
... , neutrinos with a small but nonzero mass of only a few eV/c2 (electron-volts divided by the speed of light squared; in this unit, the electron mass is 511,000) would contribute a significant fraction of the dark matter (though still not enough to allow them to be the seeds of galactic and large-scale structure formation)
From page 47...
... If the mass differences are tiny, then sensitivity to neutrino oscillations can be achieved only by looking at neutrinos that have traveled a very long distance, since the oscillations are then very gradual, although the oscillation rate can be enhanced for electrontype neutrinos traveling through dense matter, for example in the Sun. The first real hints that neutrinos oscillate came from studies of solar neutrinos.
From page 48...
... The three amass states" are mixtures of the different neutrino types, as illustrated in the second figure. Note, too, that the solar and atmospheric neutrino experiments determine mass differences and do not set the absolute scale of neutrino masses.
From page 49...
... The experiments designed to search for proton decay, the Irvine-Michigan-BrooLhaven (IMB) and Kamiokande experiments, observed that the ratio of the number of muon neutrinos to electron neutrinos fell below theoretical expectations.
From page 50...
... inspect the large photomultiplier tubes as the enormous tank is filled with water. Image courtesy of the Institute for Cosmic Ray Research, University of Tokyo.
From page 51...
... An accelerator-based neutrino oscillation experiment at Los Alamos National Laboratory, Liquid Scintillator Neutrino Detector (LSND) , has also found evidence for oscillation between the electron neutrino and the muon neutrino.
From page 52...
... New double-beta decay experiments using radioactive sources on the scale of tons will be needed to achieve a neutrino mass sensitivity in the range of 0.01 eV/c2. This is the interesting range suggested by the neutrino-oscillation evidence described above.
From page 53...
... The probable values of the neutrino masses indicated by the oscillation experiments are very small, far smaller than the analogues for any other leptons or quarks. The occurrence of neutrino oscillations is the only known phenomenon in particle physics that is not accounted for by the Standard Model in its minimal form.
From page 54...
... dark matter that seems to govern structure formation. Remarkably, some compelling ideas in particle physics both predict the existence of particles that could make up this dark matter and suggest ways of detecting them.
From page 55...
... Important new studies of CP nonconservation in B decays have recently yielded first results, showing a definite CP-violating effect in one channel, consistent with that predicted by the Standard Model. An ongoing program studying the many additional modes is needed, as are additional experiments sensitive to other B decays or to very rare kaon decays.
From page 56...
... The anion is but one of several hypothetical very light, very weakly coupled particles suggested to resolve issues in particle physics. Others are familons, dilators, and moduli fields.
From page 57...
... Are the "Constants" Constant? Modern theories of particle physics suggest that some or all of the quantities regarded as constants of nature are in reality associated with dynamical fields that change.
From page 58...
... Monitoring the arrival times of neutrinos from astrophysical sources such as supernovae also provides a means of directly probing neutrino masses (especially those of muon and tau neutrinos, which are much less accessible in the laboratory)
From page 59...
... The needed measurements or observations include confirming various effects of neutrino oscillations and identifying the neutrino species involved in each, measuring the values of the mixing parameters responsible for the observed solar neutrino abundances, and measuring the values of the neutrino masses themselves. Answers to these problems are within reach.


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