20,769 research outputs found
An Alternative Parameterization of R-matrix Theory
An alternative parameterization of R-matrix theory is presented which is
mathematically equivalent to the standard approach, but possesses features
which simplify the fitting of experimental data. In particular there are no
level shifts and no boundary-condition constants which allows the positions and
partial widths of an arbitrary number levels to be easily fixed in an analysis.
These alternative parameters can be converted to standard R-matrix parameters
by a straightforward matrix diagonalization procedure. In addition it is
possible to express the collision matrix directly in terms of the alternative
parameters.Comment: 8 pages; accepted for publication in Phys. Rev. C; expanded Sec. IV,
added Sec. VI, added Appendix, corrected typo
Super-resolution imaging of a low frequency levitated oscillator
We describe the measurement of the secular motion of a levitated nanoparticle
in a Paul trap with a CMOS camera. This simple method enables us to reach
signal-to-noise ratios as good as 10 with a displacement sensitivity
better than 10/Hz. This method can be used to extract trap
parameters as well as the properties of the levitated particles. We demonstrate
continuous monitoring of the particle dynamics on timescales of the order of
weeks. We show that by using the improvement given by super-resolution imaging,
a significant reduction in the noise floor can be attained, with an increase in
the bandwidth of the force sensitivity. This approach represents a competitive
alternative to standard optical detection for a range of low frequency
oscillators where low optical powers are require
The B Neutrino Spectrum
Knowledge of the energy spectrum of B neutrinos is an important
ingredient for interpreting experiments that detect energetic neutrinos from
the Sun. The neutrino spectrum deviates from the allowed approximation because
of the broad alpha-unstable Be final state and recoil order corrections to
the beta decay. We have measured the total energy of the alpha particles
emitted following the beta decay of B. The measured spectrum is
inconsistent with some previous measurements, in particular with a recent
experiment of comparable precision. The beta decay strength function for the
transition from B to the accessible excitation energies in Be is fit to
the alpha energy spectrum using the R-matrix approach. Both the positron and
neutrino energy spectra, corrected for recoil order effects, are constructed
from the strength function. The positron spectrum is in good agreement with a
previous direct measurement. The neutrino spectrum disagrees with previous
experiments, particularly for neutrino energies above 12 MeV.Comment: 15 pages, 13 figures, 4 tables, submitted to Phys. Rev. C, typos
correcte
Shaking a Box of Sand
We present a simple model of a vibrated box of sand, and discuss its dynamics
in terms of two parameters reflecting static and dynamic disorder respectively.
The fluidised, intermediate and frozen (`glassy') dynamical regimes are
extensively probed by analysing the response of the packing fraction to steady,
as well as cyclic, shaking, and indicators of the onset of a `glass transition'
are analysed. In the `glassy' regime, our model is exactly solvable, and allows
for the qualitative description of ageing phenomena in terms of two
characteristic lengths; predictions are also made about the influence of grain
shape anisotropy on ageing behaviour.Comment: Revised version. To appear in Europhysics Letter
Cavity cooling of an optically trapped nanoparticle
We study the cooling of a dielectric nanoscale particle trapped in an optical
cavity. We derive the frictional force for motion in the cavity field, and show
that the cooling rate is proportional to the square of oscillation amplitude
and frequency. Both the radial and axial centre-of-mass motion of the trapped
particle, which are coupled by the cavity field, are cooled. This motion is
analogous to two coupled but damped pendulums. Our simulations show that the
nanosphere can be cooled to 1/e of its initial momentum over time scales of
hundredths of milliseconds.Comment: 11 page
Testing collapse models with levitated nanoparticles: the detection challenge
We consider a nanoparticle levitated in a Paul trap in ultrahigh cryogenic
vacuum, and look for the conditions which allow for a stringent
noninterferometric test of spontaneous collapse models. In particular we
compare different possible techniques to detect the particle motion. Key
conditions which need to be achieved are extremely low residual pressure and
the ability to detect the particle at ultralow power. We compare three
different detection approaches based respectively on a optical cavity, optical
tweezer and a electrical readout, and for each one we assess advantages,
drawbacks and technical challenges
Glassy dynamics in granular compaction
Two models are presented to study the influence of slow dynamics on granular
compaction. It is found in both cases that high values of packing fraction are
achieved only by the slow relaxation of cooperative structures. Ongoing work to
study the full implications of these results is discussed.Comment: 12 pages, 9 figures; accepted in J. Phys: Condensed Matter,
proceedings of the Trieste workshop on 'Unifying concepts in glass physics
Astrophysical factor for the reaction from -matrix analysis and asymptotic normalization coefficient for . Is any fit acceptable?
The reaction provides a path from the CN
cycle to the CNO bi-cycle and CNO tri-cycle. The measured astrophysical factor
for this reaction is dominated by resonant capture through two strong
resonances at and 962 keV and direct capture to
the ground state. Recently, a new measurement of the astrophysical factor for
the reaction has been published [P. J.
LeBlanc {\it et al.}, Phys. Rev. {\bf C 82}, 055804 (2010)]. The analysis has
been done using the -matrix approach with unconstrained variation of all
parameters including the asymptotic normalization coefficient (ANC). The best
fit has been obtained for the square of the ANC fm,
which exceeds the previously measured value by a factor of . Here we
present a new -matrix analysis of the Notre Dame-LUNA data with the fixed
within the experimental uncertainties square of the ANC
fm. Rather than varying the ANC we add the contribution from a
background resonance that effectively takes into account contributions from
higher levels. Altogether we present 8 fits, five unconstrained and three
constrained. In all the fits the ANC is fixed at the previously determined
experimental value fm. For the unconstrained fit with
the boundary condition , where is the energy of the
second level, we get keVb and normalized , i.e. the result which is similar to [P. J. LeBlanc {\it et
al.}, Phys. Rev. {\bf C 82}, 055804 (2010)]. From all our fits we get the range
keVb which overlaps with the result of [P. J.
LeBlanc {\it et al.}, Phys. Rev. {\bf C 82}, 055804 (2010)]. We address also
physical interpretation of the fitting parameters.Comment: Submitted to PR
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