105 research outputs found
Particle Detection by Evaporation from Superfluid Helium
We report the first experiments in which 5-MeV alpha particles are detected via evaporation from a bath of superfluid helium. The α excites phonons and rotons in the liquid helium, and these excitations are sufficiently energetic to evaporate helium atoms when they reach the free surface of the liquid. The approximate overall efficiency of this process has been determined, and we compare this with expectations. We have also been able to detect evaporation induced by a flux of Îłâs from a 137Cs source
Phonon amplification using evaporation and adsorption of helium
We report the results of experiments designed to investigate the feasibility of amplifying a phonon signal using the evaporation of helium from a superfluid film and its subsequent readsorption onto a helium-free surface. We envision a multistage amplifier in which helium is evaporated from a wafer with a helium film only on one side and then adsorbed onto the film-free surface of a similar wafer. The phonons created by the adsorption reach the film on the opposite side of the wafer and potentially desorb more helium than was evaporated by the first wafer. The amplification would come from the high ratio of the binding energy of a helium atom to a film-free surface relative to the binding energy to the liquid. A number of experiments are reported that investigate the efficiencies of the individual steps of the process. The gain per stage is found to be about 3 for high-energy densities in which multiphonon processes are possible. At low-energy densities, the energy deposited into a film-free wafer is found to be less than the original input energy, with the ratio of output to input energy 0.2. Since in applications requiring amplification the phonon density produced by the adsorption of helium on a wafer will be low, the configuration we have studiedâphonons produced in silicon coated with a saturated He4 filmâwill not result in amplification. However, other configurations might improve the efficiency enough to make an amplifier possible
Angular Distribution of Rotons Generated by Alpha Particles in Superfluid Helium: A Possible Tool for Low Energy Particle Detection
We report measurements of the distribution of rotons generated by α particles interacting in a bath of superfluid helium. The roton flux is found to be anisotropic; it is about 4 times larger transverse to the track direction than along it. This asymmetry may provide a powerful tool in particle and astrophysics experiments where sensitivity to low energy recoil track direction is important
Implications of New Gallex Results for the MSW Solution of the Solar Neutrino Problem
We compare the implications for 7Be and pp neutrinos of the two MSW fits to
the new GALLEX solar neutrino measurements . Small mixing angle solutions tend
to suppress the former as electron-neutrinos, but not the latter, and large
angle solutions tend to reduce both by about a factor of 2. The consequences
for BOREXINO and similar solar neutrino--electron scattering experiments are
discussed.Comment: 7 pages (plus 3 figures available upon request) UTAPHY-HEP-
Solar Neutrinos: Radiative Corrections in Neutrino-Electron Scattering Experiments
Radiative corrections to the electron recoil-energy spectra and to total
cross sections are computed for neutrino-electron scattering by solar
neutrinos. Radiative corrections change monotonically the electron recoil
spectrum for incident \b8 neutrinos, with the relative probability of observing
recoil electrons being reduced by about 4 \% at the highest electron energies.
For and \be7 neutrinos, the recoil spectra are not affected
significantly. Total cross sections for solar neutrino-electron scattering are
reduced by about 2 \% compared to previously computed values. We also calculate
the recoil spectra from N and O neutrinos including radiative
corrections.Comment: 40 pages, uuencoded, Z-compress file
Solar Neutrinos: What We Have Learned
The four operating solar neutrino experiments confirm the hypothesis that the
energy source for solar luminosity is hydrogen fusion. However, the measured
rate for each of the four solar neutrino experiments differs significantly (by
factors of 2.0 to 3.5) from the corresponding theoretical prediction that is
based upon the standard solar model and the simplest version of the standard
electroweak theory. If standard electroweak theory is correct, the energy
spectrum for \b8 neutrinos created in the solar interior must be the same (to
one part in ) as the known laboratory \b8 neutrino energy spectrum.
Direct comparison of the chlorine and the Kamiokande experiments, both
sensitive to \b8 neutrinos, suggests that the discrepancy between theory and
observations depends upon neutrino energy, in conflict with standard
expectations. Monte Carlo studies with 1000 implementations of the standard
solar model confirm that the chlorine and the Kamiokande experiments cannot be
reconciled unless new weak interaction physics changes the shape of the \b8
neutrino energy spectrum. The results of the two gallium solar neutrino
experiments strengthen the conclusion that new physics is required and help
determine a relatively small allowed region for the MSW neutrino parameters.Comment: LaTeX file, 19 pages. For hardcopy with figures contact
[email protected]. Institute for Advanced Study number AST 93/6
Current Status of the Solar Neutrino Problem with Super-Kamiokande
We perform an updated model-independent analysis using the latest solar
neutrino data obtained by Cl and Ga radiochemical experiments,
and most notably by a large water-Cherenkov detector SuperKamiokande with their
504 days of data taking. We confirm that the astrophysical solutions to the
solar neutrino problem are extremely disfavored by the data and a
low-temperature modification of the standard solar model is excluded by more
than 5 . We also propose a new way of illuminating the suppression
pattern of various solar neutrino flux without invoking detailed flavor
conversion mechanisms. It indicates that the strong suppression of Be
neutrinos is no more true when the neutrino flavor conversion is taken into
account.Comment: RevTex file, 10 pages, 7 postscript figure
How Well Do We (and Will We) Know Solar Neutrino Fluxes and Oscillation Parameters?
Assuming neutrino oscillations occur, the pp electron neutrino flux is
uncertain by at least a factor of two, the flux by a factor of
five, and the flux by a factor of forty-five. Calculations of the
expected results of future solar neutrino experiments (SuperKamiokande, SNO,
BOREXINO, ICARUS, HELLAZ, and HERON) are used to illustrate the extent to which
these experiments will restrict the range of the allowed neutrino mixing
parameters. We present an improved formulation of the ``luminosity constraint''
and show that at 95\% confidence limit this constraint establishes the best
available limits on the rate of creation of pp neutrinos in the solar interior
and provides the best upper limit to the neutrino flux.Comment: 37 pages, uuencoded Z-compressed postscript file (with figures);
Submitted to Physical Review
Phenomenology of Maximal and Near-Maximal Lepton Mixing
We study the phenomenological consequences of maximal and near-maximal mixing
of the electron neutrino with other (=tau and/or muon) neutrinos. We
describe the deviations from maximal mixing in terms of a parameter
and quantify the present experimental
status for . We find that the global analysis of solar neutrino
data allows maximal mixing with confidence level better than 99% for
eV^2\lsim\Delta m^2\lsim2\times10^{-7} eV. In the mass ranges \Delta
m^2\gsim 1.5\times10^{-5} eV and eV^2\lsim\Delta
m^2\lsim2\times10^{-7} eV the full interval is allowed
within 4(99.995 % CL). We suggest ways to measure in future
experiments. The observable that is most sensitive to is the rate
[NC]/[CC] in combination with the Day-Night asymmetry in the SNO detector. With
theoretical and statistical uncertainties, the expected accuracy after 5 years
is . We also discuss the effects of maximal and
near-maximal -mixing in atmospheric neutrinos, supernova neutrinos, and
neutrinoless double beta decay.Comment: 49 pages Latex file using RevTeX. 16 postscript figures included. (
Fig.2 and Fig.4 bitmapped for compression,better resolution at
http://ific.uv.es/~pppac/). Improved presentation: some statements included
and labels added in figures. Some misprint corrected. Final version to appear
in Phys. Rev D. Report no: IFIC/00-40, IASSNS-HEP-00-5
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