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4 Science Potential of a Deep Underground Laboratory
Pages 32-57

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From page 32...
... A clean, quiet, and isolated setting is needed to study such rare phenomena free from environmental background. Such a setting can be obtained only deep underground, where we can escape the rain of cosmic rays from outer space.
From page 33...
... Scientists addressing issues of intense international interest solar neutrinos, double beta decay, and dark matter are poised to develop next-generation detectors that require Tow background, and they need an underground facility for technology development in the next few years. Once the neutrino mixing and mass parameters have been measured with some accuracy, a Tong-baseline experiment should be developed.
From page 34...
... This tidy picture has been dramatically changed by recent experimental discoveries. For both atmospheric and solar neutrinos, there is now strong evidence that they change from one type to another (oscilIate)
From page 35...
... As discussed in the subsequent sections, these issues can be studied in a variety of experiments involving more accurate studies of solar and atmospheric neutrinos, double beta decay, and accelerator-based neutrino experiments, especially those with Tong baselines. A deep underground laboratory will play a crucial role in these proposed experiments.
From page 36...
... Solar neutrinos were first detected in an experiment in the Homestake Gold Mine in South Dakota by Raymond Davis, Jr. That experiment also gave the earliest indication for a finite neutrino mass when only a third of the expected number of neutrinos was seen.
From page 37...
... The three regions labeled across the top indicate the expected energy-range sensitivity of different solar neutrino detectors. The different curves on the plot correspond to the neutrino energy spectra for neutrinos from different fusion processes within the Sun, such as the pp reaction or the pep chain.
From page 38...
... In the study of neutrino properties, neutrino beams from particle accelerators can provide information complementary to that from future solar neutrino experiments that address measurements not accessible to accelerator experiments (see Figure 4.3~. Protons from accelerators produce an almost pure beam of muon neutrinos, while solar neutrinos are purely electron neutrinos.
From page 39...
... A steel absorber is used to stop the remaining plans and newly born muons. In the long-baseline experiment, the berm of earth in the figure is actually formed by Earth itself; a neutrino beam would travel thousands of kilometers before arriving at the target, where the neutrinos are detected and identified by their interactions with the detector.
From page 40...
... The oscillation effects in this case occur only over distances comparable to the size of Earth. For quantitative measurements of neutrino mass and mixing parameters, however, accelerator-based neutrino oscillation experiments are crucial.
From page 41...
... An operating underground laboratory would facilitate this planning. Also, laboratory infrastructure and staff would greatly expedite the installation, commissioning, and operation of large detectors.
From page 42...
... A more interesting process is that of neutrinoless double beta decay, in which no neutrinos are emitted and the two beta particles share the total energy. If neutrinoless double beta decay exists, it implies that neutrinos are Majorana particles, and its rate is proportional to the square of the Majorana mass.
From page 43...
... Thus at least one neutrino has a mass greater than 50 meV, and this value sets the goal for the next generation of double beta decay experiments. Although the oscillation properties can be pinned down better by further oscillation experiments, to determine the neutrino mass requires either a direct mass measurement or an observation of neutrinoless double beta decay.
From page 44...
... Deep underground laboratory space is essential to success, and a national underground facility is a natural way to meet this need. DARK MATTER Over the past decade, strong evidence has led to the conclusion that neither ordinary matter nor even massive neutrinos can account for most of the missing matter.
From page 45...
... Since the tools to distinguish these backgrounds are never perfect, it is crucial to reduce the level of contamination through screening and fabrication techniques, as with the double beta decay experiments. Second, neutrons, which come from a variety of sources, are not directly distinguishable from WIMPs because they, too, recoil from nuclei.
From page 46...
... Proposals for such experiments, which typically aim for 100-kg submodules, are expected in the next 2 to 4 years and could run concurrently with the Large Hadron Collider, which will explore in a complementary fashion the same underlying physics of supersymmetry or other new physics at the electroweak interaction scale. To a degree, improvements in detector technology or assaying and screening of detector components can reduce the level of electromagnetic backgrounds at any given depth.
From page 47...
... When astronomer Fritz Zwicky found the first evidence for dark matter many decades ago, little did he realize that the answer to his mystery would involve not faint stars but most likely a new form of matter whose existence is key to understanding the union of the basic forces of nature. PROTON DECAY It is an important question whether the kinds of matter we are made of, ordinary atoms with ordinary nuclei and electrons, are stable.
From page 48...
... However, within the context of the Standard Model, proton stability arises because no known particle species can mediate the process for the proton to decay. So, researchers expect that particles in nature that have yet to be discovered could mediate proton decay.
From page 49...
... , and they confirmed the theory of Type II supernova as the death of a massive star forming a neutron star. These two proton decay experiments studied neutrinos produced in the atmosphere from the collision of cosmic rays and saw the first hint of neutrino oscillations and hence finite neutrino mass.
From page 50...
... The solar neutrino detectors using water Cerenkov technology, such as SuperKamiokande and SNO, are able to look at higher-energy neutrinos only. Direct experimental confirmation of the basic features of the solar neutrino spectrum is lacking.
From page 51...
... In 1987, light from a supernova in the Large Magellanic Cloud (a nearby dwarf galaxy) was seen by telescopes, and simultaneously, 17 neutrinos were detected in the large water volumes of two operating underground proton decay experiments.
From page 52...
... Neutrinos are a unique source of information about supernovae and will provide a better window on how the elements heavier than oxygen that are essential to life came to exist on Earth. OTHER SCIENCE AT AN UNDERGROUND LABORATORY Other uses of a laboratory deep underground have been suggested.
From page 53...
... Standard rock has a density of 2.650 g cm-2, but actual rock density depends significantly on location. The horizontal bar indicates the range of depths that would be available for experiments in a multipurpose underground laboratory.
From page 54...
... ~; the Edelweiss boTometric-ionization hybrid dark matter detector; and a Tow-background counting facility. The laboratory is 130 km from CERN and is a possible site for a megatonscaTe detector for neutrino oscillations, solar neutrinos, supernovae, and proton decay.
From page 55...
... Other new experiments at Kamioka include a small lithium fluoride darkmatter experiment, a gravitational wave detector, and a 100-kg prototype liquid xenon detector for dark matter, low-energy solar neutrinos, and double beta decay. The xenon project (Xenon Massive Detector for Solar Neutrinos XMASS)
From page 56...
... Started as a proton decay experiment, IMB also served as an atmospheric neutrino detector and was one of only two experiments to observe the neutrino flux from supernova 1987A (the other being the Japanese Kamioka project)
From page 57...
... Of the five ton-scale double beta decay experiments proposed, one is committed to Gran Sasso, two are sufficiently advanced that underground sites will be needed soon, and the other two are in the R&D stage. The low-energy solar neutrino experiments that will follow Borexino and KamLAND are also still in the R&D stage.


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