Solar neutrinos: experimental approaches

This article discusses the new experiments, under way or proposed, that will measure the flux of solar neutrinos and so probe the "solar neutrino puzzle." Both radiochemical and electronic detector experiments are analyzed in terms of possible findings relevant to astrophysics and neutrino properties. Important elements are sensitivity to the principal components of the solar neutrino spectrum, directionality of the detector response, and an energy-measuring capability that might provide a unique identifying signal. Experiments beyond those currently under way will probably be needed, and development of real-time detectors is particularly important.     

Solar neutrinos: questions and hypotheses

The "solar neutrino puzzle" has been a challenge for almost 20 years, posing broad and fundamental questions about astrophysics and neutrino properties. This article sketches some of the ideas that have been put forward to solve the problem. These ideas can be grouped into two main classes: those involving changes in the standard solar model or in the basic nuclear reaction data, and those that attribute the puzzle to as yet unobserved properties of the neutrinos.     

Limits on sensitivity of large silicon bolometers for solar neutrino detection

Estimates are given for ultimate limits on background in proposed direct-counting measurements of neutrino scattering from large silicon crystals. Methods of background reduction are discussed. In the best case, the limiting backgrounds due to activities from cosmic-ray spallation of silicon would be less than the expected true event rate for reactor neutrino measurements of coherent neutral-current scattering from silicon nuclei. Considerable reduction of the estimated high-energy backgrounds would be required for a good signal-to-noise ratio in solar neutrino detection.     

Astrophysics and cosmology closing in on neutrino masses

Massive neutrinos are expected in most grand unified theories that attempt to unify the strong and electroweak interactions. So far, heroic laboratory experiments have yielded only upper bounds on the masses of the elusive neutrinos. These bounds, however, are not very restrictive and cannot even exclude the possibility that the dark matter in the universe consists of neutrinos. The astrophysical and cosmological bounds on the masses of the muon and tau neutrinos, mv(vmicro) and mv(vtau), which already are much more restrictive than the laboratory bounds, and the laboratory bound on the mass of the electron neutrino, mv(vc), can be improved significantly by future astrophysical and cosmological observations that perhaps will pin down the neutrino masses. Indeed, the recent results from the solar neutrino experiments combined with the seesaw mechanism for generating neutrino masses suggest that mv(vc) approximately 10(-8) electron volts, mv(vmicro) approximately 10(-3) electron volts, and mv(vtau) approximately 10 electron volts, which can be tested in the near future by solar neutrino and accelerator experiments.     

What has caused the secular increase in solar nitrogen-15?

Well-documented variations in the (15)N/(14)N ratio in lunar surface samples apparently result from a secular increase in that ratio in the solar wind during the past few billion years. The cause of this change seems to lie in the solar convective zone but is inexplicable within our present understanding of solar processes. This problem therefore ranks with the solar neutrino deficiency as a major challenge to our solar paradigm.     

Solar neutrinos--from puzzle to paradox

The solar neutrino puzzle is deepening into a paradox that refutes the basic logic of the reaction chain that powers the sun by the fusion of protons into heavy elements. Experiments now reveal a serious anomaly in the relative neutrino fluxes from the different steps in the chain. Neutrinos from boron-8 at the end of the chain are seen but hardly any are seen from beryllium-7, without which the observed boron-8 cannot be made. The only apparent way to avoid a paradoxical "missing link" in the sun's energy chain is a nonzero neutrino mass, an idea that can be tested in future experiments.     

中微子振荡与太阳中微子问题

认为太阳中微子问题主要是标准太阳模型没有考虑 7Be( 3He,p) 9B核反应道的竞争 ,并且在计算 7Be中微子和 pep中微子时 ,并没有考虑到太阳电子温度与离子温度的差异 .如果考虑了这种差异 ,则太阳中微子问题可以得到很好地解决 ,而不需要修改太阳的其它重要参数     

Solar neutrino production of long-lived isotopes and secular variations in the sun

Long-lived isotopes produced in the earth's crust by solar neutrinos may provide a method of probing secular variations in the rate of energy production in the sun's core. Only one isotope, calcium-41, appears to be suitable from the dual stand-points of reliable nuclear physics and manageable backgrounds. The proposed measurement also may be interesting in view of recent evidence for neutrino oscillations.     

Implications of Solar Evolution for the Earth's Early Atmosphere

The roughly 25 percent increase in luminosity over the life of the sun shared by many different solar models is shown to be a very general result, independent of the uncertainties suggested by the solar neutrino experiment. Superficially, this leads to a conflict with the climatic history of the earth, and if basic concepts of stellar evolution are not fundamentally in error, compensating effects must have occurred, as first pointed out by Sagan and Mullen. One possible interpretation supported by recent detailed models of the earth's atmosphere is that the greenhouse effect was substantially more important than at present even as recently as 1 billion to 2 billion years ago.     

UV Spectrum and Proposed Role of Diethylberyllium in a 7Li-7Be Solar Neutrino Experiment

Although measurement of the solar neutrino flux via the (7)Li(v(e),e(-))(7)Be reaction was proposed many years ago, no experiment has been implemented since it has been difficult to identify a sensitive (7)Be detection technique. Here it is proposed that the (7)Be atom be incorporated into a volatile molecule, placed in a buffer-gas-filled cell, and then extracted by photodissociation; after excitation by a tunable laser, bursts of photons would be detected. The absorption spectrum of the molecular candidate diethylberyllium has been measured between 186 and 270 nanometers in a spectrophotometer to determine the required photodissociation laser wavelength and intensity.     

The first high-energy neurtrino experiment

This article describes the state of knowledge of weak interactions in 1960, the conception and implementation of the first high-energy neutrino experiment, and the not altogether unexpected result that the muon neutrino is different from the electron neutrino.     

Detectability of supernova neutrinos with an existing proton decay detector

The 8000-ton water IMB nucleon decay detector has good sensitivity to the neutrino burst associated with the collapse of stars. It is particularly sensitive to the v(e) charged current interactions with protons but can also record other neutrino interactions through ve scattering. Signal, noise, physics objectives, and detector modifications that would enhance burst detection are discussed. The objectives include astrophysical questions about the pulse structure and power. It also may be possible with a distant source to study neutrino masses and neutrino oscillations.     

Neutrino astrophysics experiments beneath the sea and ice

Neutrino astronomy beyond the Sun was first imagined in the late 1950s. A neutrino detector at the bottom of Lake Baikal, the deployment of detectors in the Mediterranean Sea, and the construction of a kilometer-scale neutrino telescope at the South Pole exemplify current efforts to realize this dream.     

PARTICLE PHYSICS: Elusive Particle Leaves Telltale Trace

Nearly massless and incredibly rare, the tau neutrino seldom interacts with more common matter, making it difficult to detect. Now, an international team of physicists has laid claim to the first "direct" detection of the tau neutrino.     

Neutrino astrophysics: a new tool for exploring the universe

In the past four decades a new type of astronomy has emerged, where instead of looking up into the sky, "telescopes" are buried miles underground or deep under water or ice and search not for photons (that is, light), but rather for particles called neutrinos. Neutrinos are nearly massless particles that interact very weakly with matter. The detection of neutrinos emitted by the Sun and by a nearby supernova provided direct tests of the theory of stellar evolution and led to modifications of the standard model describing the properties of elementary particles. At present, several very large neutrino detectors are being constructed, aiming at the detection of the most powerful sources of energy and particles in the universe. The hope is that the detection of neutrinos from these sources, which are extra-Galactic and are most likely powered by mass accretion onto black holes, will not only allow study of the sources, but, much like solar neutrinos, will also provide new information about fundamental properties of matter.     

Observations in particle physics from two neutrinos to the standard model

The two-neutrino experiment established a relationship between particles, muon and muon neutrino, electron and electron neutrino, which evolved into the standard model of particle physics. The theme of this article is a personal one, which reviews a series of experiments at the Columbia Synchrocyclotron, the Brookhaven Cosmotron, the Alternating Gradient Synchrotron, the CERN intersecting storage rings, the Fermilab 400-gigavolt proton synchrotron, and the Cornell electron storage rings, all of which were important in the evolution of the standard model. In some cases the fermion particles were discovered (the second neutrino vmicro, b quark); in other cases fields of research were opened (muon spin resonance, neutral kaons and charge-parity violation, dimuons and the Drell-Yan process), which led to further development of the standard model. Finally, the current ignorance about the properties of now three neutrinos is reviewed.     

The early days of experimental neutrino physics

The neutrino hypothesis, put forward by Pauli to account for the apparent loss of energy and momentum in beta decay, was verified by a series of measurements at a nuclear reactor nearly 25 years ago. An account is given of the first observations of the interaction of neutrinos in a target remote from the fission process that produced them. These experiments completed the observations of the particles involved in beta decay and paved the way for use of the free neutrino to probe the nature of the weak interaction.     

Physicists rock the standard model in dallas

The 1400 physicists who converged on Dallas 2 weeks ago for the International High Energy Physics meeting came from all over. Ask them about the state of their field, however, and you'll find a common dream-to go beyond the standard model of particles and forces. For physicists "searching for chinks in the model's armor," as several put it, the elusive, unobtrusive neutrino is a promising object of study. And while the meeting saw the possibility of a superheavy "17-keV" neutrino fade, cosmic ray-produced neutrinos gave new hints of physics in that over-the-rainbow region beyond the standard model.     

Cosmic Neutrino Radiation

New and more powerful methods for eliminating background intensity are needed in order to make possible the development of neutrino astronomy into a new, far-reaching branch of science.     

Telecommunication with neutrino beams

Collimated neutrino beams in the energy range 1 to 100 gigaelectron volts, now available from high-energy proton accelerators, are proposed as a potential means for telecommunication over global distances. Quantitative estimates of the feasibility of this proposal based on a particular detector configuration are presented.