1,562 research outputs found
Measuring the proton spectrum in neutron decay - latest results with aSPECT
The retardation spectrometer aSPECT was built to measure the shape of the
proton spectrum in free neutron decay with high precision. This allows us to
determine the antineutrino electron angular correlation coefficient a. We aim
for a precision more than one order of magnitude better than the present best
value, which is Delta_a /a = 5%.
In a recent beam time performed at the Institut Laue-Langevin during April /
May 2008 we reached a statistical accuracy of about 2% per 24 hours measurement
time. Several systematic effects were investigated experimentally. We expect
the total relative uncertainty to be well below 5%.Comment: Accepted for publication in the Conference Proceedings of the
International Workshop on Particle Physics with Slow Neutrons 2008 held at
the ILL, France. To be published in Nuclear Instruments and Methods in
Physics Research, Section
Characterisation of HTSC ceramics from their resistive transition
The resistivity vs. temperature relation in bulk ceramic HTSC under
self-field conditions as well as in weak external magnetic fields is modelled
by local Lorentz force induced fluxon motion with temperature dependent
pinning. A pinning force density and two viscous drag coefficients in
intergrain and intragrain regions, respectively, can be used as characteristic
parameters describing the temperature, current, and external field dependences
of the sample resistance.Comment: 12 pages, LaTeX2e, 6 figures (epsfig), to be published in Supercond.
Sci. and Techno
A quantum mechanical description of the experiment on the observation of gravitationally bound states
Quantum states in the Earth's gravitational field were observed, when
ultra-cold neutrons fall under gravity. The experimental results can be
described by the quantum mechanical scattering model as it is presented here.
We also discuss other geometries of the experimental setup which correspond to
the absence or the reversion of gravity. Since our quantum mechanical model
describes, particularly, the experimentally realized situation of reversed
gravity quantitatively, we can practically rule out alternative explanations of
the quantum states in terms of pure confinement effects.Comment: LaTeX, 10 pages, 4 figures, v2: references adde
A clean, bright, and versatile source of neutron decay products
We present a case study on a new type of cold neutron beam station for the
investigation of angular correlations in the beta-decay of free neutrons. With
this beam station, called PERC, the 'active decay volume' lies inside the
neutron guide, and the charged neutron decay products are magnetically guided
towards the end of the neutron guide. Hence, the guide delivers at its exit a
beam of decay electrons and protons, under well-defined and precisely variable
conditions, which can be well separated from the cold neutron beam. In this way
a general-purpose source of neutron decay products is obtained which can be
used for various different experiments in neutron decay correlation
spectroscopy. A gain in phase space density of several orders of magnitude can
be achieved with PERC, as compared to existing neutron decay spectrometers.
Neutron beam related background is separately measurable in PERC, and magnetic
mirror effects on the charged neutron decay products and edge effects in the
active neutron beam volume are both strongly suppressed. Therefore the spectra
and angular distributions of the emerging decay particles will be
distortion-free on the level of 10^-4, more than 10 times better than achieved
today.Comment: 20 pages, 6 figure
Vortex dynamics in layered superconductors with correlated defects: influence of interlayer coupling
We report a detailed study of the vortex dynamics and vortex phase diagrams
of two amorphous Ta_0.3Ge_0.7/Ge multilayered films with intrinsic coplanar
defects, but different interlayer coupling. A pinned Bose-glass phase in the
more weakly coupled sample exists only below a cross-over field H* in striking
contrast to the strongly coupled film. Above H* the flux lines are thought to
break up into pancake vortices and the cross-over field is significantly
increased when the field is aligned along the extended defects. The two films
show different vortex creep excitations in the Bose-glass phase.Comment: zip file: 1 RevTex, 5 figures (png
Constrains on non-Newtonian gravity from the experiment on neutron quantum states in the Earth's gravitational field
An upper limit to non-Newtonian attracive forces is obtained from the
measurement of quantum states of neutrons in the Earth's gravitational field.
This limit improves the existing constrains in the nanometer range
Quantum motion of a neutron in a wave-guide in the gravitational field
We study theoretically the quantum motion of a neutron in a horizontal
wave-guide in the gravitational field of the Earth. The wave-guide in question
is equipped with a mirror below and a rough absorber above. We show that such a
system acts as a quantum filter, i.e. it effectively absorbs quantum states
with sufficiently high transversal energy but transmits low-energy states. The
states transmitted are mainly determined by the potential well formed by the
gravitational field of the Earth and the mirror. The formalism developed for
quantum motion in an absorbing wave-guide is applied to the description of the
recent experiment on the observation of the quantum states of neutrons in the
Earth's gravitational field
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