300 research outputs found
Fast algorithm for calculating two-photon absorption spectra
We report a numerical calculation of the two-photon absorption coefficient of
electrons in a binding potential using the real-time real-space higher-order
difference method. By introducing random vector averaging for the intermediate
state, the task of evaluating the two-dimensional time integral is reduced to
calculating two one-dimensional integrals. This allows the reduction of the
computation load down to the same order as that for the linear response
function. The relative advantage of the method compared to the straightforward
multi-dimensional time integration is greater for the calculation of non-linear
response functions of higher order at higher energy resolution.Comment: 4 pages, 2 figures. It will be published in Phys. Rev. E on 1, March,
199
Constraints on neutrino oscillation parameters from the measurement of day-night solar neutrino fluxes at Super-Kamiokande
A search for day-night variations in the solar neutrino flux resulting from
neutrino oscillations has been carried out using the 504 day sample of solar
neutrino data obtained at Super-Kamiokande. The absence of a significant
day-night variation has set an absolute flux independent exclusion region in
the two neutrino oscillation parameter space.Comment: 11 pages, 3 figures, submitted to PRL, single-spacin
Constraints on Neutrino Oscillations Using 1258 Days of Super-Kamiokande Solar Neutrino Data
We report the result of a search for neutrino oscillations using precise
measurements of the recoil electron energy spectrum and zenith angle variations
of the solar neutrino flux from 1258 days of neutrino-electron scattering data
in Super-Kamiokande. The absence of significant zenith angle variation and
spectrum distortion places strong constraints on neutrino mixing and mass
difference in a flux-independent way. Using the Super-Kamiokande flux
measurement in addition, two allowed regions at large mixing are found.Comment: 6 pages, 4 figures, submitted to PR
Solar 8B and hep Neutrino Measurements from 1258 Days of Super-Kamiokande Data
Solar neutrino measurements from 1258 days of data from the Super-Kamiokande
detector are presented. The measurements are based on recoil electrons in the
energy range 5.0-20.0MeV. The measured solar neutrino flux is 2.32 +-
0.03(stat.) +0.08-0.07(sys.)*10^6cm^{-2}s^{-1}, which is
45.1+-0.5(stat.)+1.6-1.4(sys.)% of that predicted by the BP2000 SSM. The day vs
night flux asymmetry is 0.033+-0.022(stat.)+0.013-0.012(sys.). The recoil
electron energy spectrum is consistent with no spectral distortion
(\chi^2/d.o.f. = 19.0/18). The seasonal variation of the flux is consistent
with that expected from the eccentricity of the Earth's orbit (\chi^2/d.o.f. =
3.7/7). For the hep neutrino flux, we set a 90% C.L. upper limit of 40
*10^3cm^{-2}s^{-1}, which is 4.3 times the BP2000 SSM prediction.Comment: 7 pages, 5 figures, submitted to PRL (part of this paper
Light emission from a scanning tunneling microscope: Fully retarded calculation
The light emission rate from a scanning tunneling microscope (STM) scanning a
noble metal surface is calculated taking retardation effects into account. As
in our previous, non-retarded theory [Johansson, Monreal, and Apell, Phys. Rev.
B 42, 9210 (1990)], the STM tip is modeled by a sphere, and the dielectric
properties of tip and sample are described by experimentally measured
dielectric functions. The calculations are based on exact diffraction theory
through the vector equivalent of the Kirchoff integral. The present results are
qualitatively similar to those of the non-retarded calculations. The light
emission spectra have pronounced resonance peaks due to the formation of a
tip-induced plasmon mode localized to the cavity between the tip and the
sample. At a quantitative level, the effects of retardation are rather small as
long as the sample material is Au or Cu, and the tip consists of W or Ir.
However, for Ag samples, in which the resistive losses are smaller, the
inclusion of retardation effects in the calculation leads to larger changes:
the resonance energy decreases by 0.2-0.3 eV, and the resonance broadens. These
changes improve the agreement with experiment. For a Ag sample and an Ir tip,
the quantum efficiency is 10 emitted photons in the visible
frequency range per tunneling electron. A study of the energy dissipation into
the tip and sample shows that in total about 1 % of the electrons undergo
inelastic processes while tunneling.Comment: 16 pages, 10 figures (1 ps, 9 tex, automatically included); To appear
in Phys. Rev. B (15 October 1998
Evidence for an oscillatory signature in atmospheric neutrino oscillation
Muon neutrino disappearance probability as a function of neutrino flight
length L over neutrino energy E was studied. A dip in the L/E distribution was
observed in the data, as predicted from the sinusoidal flavor transition
probability of neutrino oscillation. The observed L/E distribution constrained
nu_mu nu_tau neutrino oscillation parameters; 1.9x10^-3 < Delta m^2 <
3.0x10^-3 eV^2 and \sin^2(2theta) > 0.90 at 90% confidence level.Comment: 5 pages, 5 figures, submitted to PR
Search for nucleon decay via modes favored by supersymmetric grand unification models in Super-Kamiokande-I
We report the results for nucleon decay searches via modes favored by
supersymmetric grand unified models in Super-Kamiokande. Using 1489 days of
full Super-Kamiokande-I data, we searched for , , and modes. We found no
evidence for nucleon decay in any of these modes. We set lower limits of
partial nucleon lifetime 2.3, 1.3,
1.3 and 1.0 years at 90% confidence level for , , and modes, respectively. These results give a strong constraint on
supersymmetric grand unification models.Comment: 14 pages, 13 figure
Tau Neutrinos Favored over Sterile Neutrinos in Atmospheric Muon Neutrino Oscillations
The previously published atmospheric neutrino data did not distinguish
whether muon neutrinos were oscillating into tau neutrinos or sterile
neutrinos, as both hypotheses fit the data. Using data recorded in 1100
live-days of the Super-Kamiokande detector, we use three complementary data
samples to study the difference in zenith angle distribution due to neutral
currents and matter effects. We find no evidence favoring sterile neutrinos,
and reject the hypothesis at the 99% confidence level. On the other hand, we
find that oscillation between muon and tau neutrinos suffices to explain all
the results in hand.Comment: 9 pages with 2 figures, submitted to PR
Search for Supernova Relic Neutrinos at Super-Kamiokande
A search for the relic neutrinos from all past core-collapse supernovae was
conducted using 1496 days of data from the Super-Kamiokande detector. This
analysis looked for electron-type anti-neutrinos that had produced a positron
with an energy greater than 18 MeV. In the absence of a signal, 90% C.L. upper
limits on the total flux were set for several theoretical models; these limits
ranged from 20 to 130 nu_e bar cm^-2 s^-1. Additionally, an upper bound of 1.2
nu_e bar cm^-2 s^-1 was set for the supernova relic neutrino flux in the energy
region E_nu > 19.3 MeV.Comment: 4 pages, 2 figures. Submitted to Physical Review Letters. New version
includes corrections to Figure 1. Also, text has been shortened to conform
with the space limitations of PR
- …