172 research outputs found
Magnetic field stabilization for high-accuracy mass measurements on exotic nuclides
The magnetic-field stability of a mass spectrometer plays a crucial role in
precision mass measurements. In the case of mass determination of short-lived
nuclides with a Penning trap, major causes of instabilities are temperature
fluctuations in the vicinity of the trap and pressure fluctuations in the
liquid helium cryostat of the superconducting magnet. Thus systems for the
temperature and pressure stabilization of the Penning trap mass spectrometer
ISOLTRAP at the ISOLDE facility at CERN have been installed. A reduction of the
fluctuations by at least one order of magnitude downto dT=+/-5mK and
dp=+/-50mtorr has been achieved, which corresponds to a relative frequency
change of 2.7x10^{-9} and 1.5x10^{-10}, respectively. With this stabilization
the frequency determination with the Penning trap only shows a linear temporal
drift over several hours on the 10 ppb level due to the finite resistance of
the superconducting magnet coils.Comment: 23 pages, 13 figure
Search for nucleon decays with EXO-200
A search for instability of nucleons bound in Xe nuclei is reported
with 223 kgyr exposure of Xe in the EXO-200 experiment. Lifetime
limits of 3.3 and 1.9 yrs are established for
nucleon decay to Sb and Te, respectively. These are the most
stringent to date, exceeding the prior decay limits by a factor of 9 and 7,
respectively
Deep Neural Networks for Energy and Position Reconstruction in EXO-200
We apply deep neural networks (DNN) to data from the EXO-200 experiment. In
the studied cases, the DNN is able to reconstruct the relevant parameters -
total energy and position - directly from raw digitized waveforms, with minimal
exceptions. For the first time, the developed algorithms are evaluated on real
detector calibration data. The accuracy of reconstruction either reaches or
exceeds what was achieved by the conventional approaches developed by EXO-200
over the course of the experiment. Most existing DNN approaches to event
reconstruction and classification in particle physics are trained on Monte
Carlo simulated events. Such algorithms are inherently limited by the accuracy
of the simulation. We describe a unique approach that, in an experiment such as
EXO-200, allows to successfully perform certain reconstruction and analysis
tasks by training the network on waveforms from experimental data, either
reducing or eliminating the reliance on the Monte Carlo.Comment: Accepted version. 33 pages, 28 figure
The evolution of the luminosity functions in the FORS Deep Field from low to high redshift: I. The blue bands
We use the very deep and homogeneous I-band selected dataset of the FORS Deep
Field (FDF) to trace the evolution of the luminosity function over the redshift
range 0.5 < z < 5.0. We show that the FDF I-band selection down to I(AB)=26.8
misses of the order of 10 % of the galaxies that would be detected in a K-band
selected survey with magnitude limit K(AB)=26.3 (like FIRES). Photometric
redshifts for 5558 galaxies are estimated based on the photometry in 9 filters
(U, B, Gunn g, R, I, SDSS z, J, K and a special filter centered at 834 nm). A
comparison with 362 spectroscopic redshifts shows that the achieved accuracy of
the photometric redshifts is (Delta z / (z_spec+1)) < 0.03 with only ~ 1 %
outliers. This allows us to derive luminosity functions with a reliability
similar to spectroscopic surveys. In addition, the luminosity functions can be
traced to objects of lower luminosity which generally are not accessible to
spectroscopy. We investigate the evolution of the luminosity functions
evaluated in the restframe UV (1500 Angstroem and 2800 Angstroem), u', B, and
g' bands. Comparison with results from the literature shows the reliability of
the derived luminosity functions. Out to redshifts of z ~ 2.5 the data are
consistent with a slope of the luminosity function approximately constant with
redshift, at a value of -1.07 +- 0.04 in the UV (1500 Angstroem, 2800
Angstroem) as well as u', and -1.25 +- 0.03 in the blue (g', B). We do not see
evidence for a very steep slope (alpha < -1.6) in the UV at z ~ 3.0 and z ~ 4.0
favoured by other authors. There may be a tendency for the faint-end slope to
become shallower with increasing redshift but the effect is marginal. We find a
brightening of M_star and a decrease of Phi_star with redshift for all analyzed
wavelengths. [abridged]Comment: 30 pages, re-submitted to A&A after referee comments have been taken
into account, full-resolution version available at
http://www.usm.uni-muenchen.de/people/gabasch/publications/gabasch_lfblue.p
Measurement of the Spectral Shape of the beta-decay of 137Xe to the Ground State of 137Cs in EXO-200 and Comparison with Theory
We report on a comparison between the theoretically predicted and
experimentally measured spectra of the first-forbidden non-unique -decay
transition ^{137}\textrm{Xe}(7/2^-)\to\,^{137}\textrm{Cs}(7/2^+). The
experimental data were acquired by the EXO-200 experiment during a deployment
of an AmBe neutron source. The ultra-low background environment of EXO-200,
together with dedicated source deployment and analysis procedures, allowed for
collection of a pure sample of the decays, with an estimated
signal-to-background ratio of more than 99-to-1 in the energy range from 1075
to 4175 keV. In addition to providing a rare and accurate measurement of the
first-forbidden non-unique -decay shape, this work constitutes a novel
test of the calculated electron spectral shapes in the context of the reactor
antineutrino anomaly and spectral bump.Comment: Version as accepted by PR
Characterization of an Ionization Readout Tile for nEXO
A new design for the anode of a time projection chamber, consisting of a
charge-detecting "tile", is investigated for use in large scale liquid xenon
detectors. The tile is produced by depositing 60 orthogonal metal
charge-collecting strips, 3~mm wide, on a 10~\si{\cm} 10~\si{\cm}
fused-silica wafer. These charge tiles may be employed by large detectors, such
as the proposed tonne-scale nEXO experiment to search for neutrinoless
double-beta decay. Modular by design, an array of tiles can cover a sizable
area. The width of each strip is small compared to the size of the tile, so a
Frisch grid is not required. A grid-less, tiled anode design is beneficial for
an experiment such as nEXO, where a wire tensioning support structure and
Frisch grid might contribute radioactive backgrounds and would have to be
designed to accommodate cycling to cryogenic temperatures. The segmented anode
also reduces some degeneracies in signal reconstruction that arise in
large-area crossed-wire time projection chambers. A prototype tile was tested
in a cell containing liquid xenon. Very good agreement is achieved between the
measured ionization spectrum of a Bi source and simulations that
include the microphysics of recombination in xenon and a detailed modeling of
the electrostatic field of the detector. An energy resolution =5.5\%
is observed at 570~\si{keV}, comparable to the best intrinsic ionization-only
resolution reported in literature for liquid xenon at 936~V/\si{cm}.Comment: 18 pages, 13 figures, as publishe
Sensitivity and discovery potential of the proposed nEXO experiment to neutrinoless double beta decay
The next-generation Enriched Xenon Observatory (nEXO) is a proposed
experiment to search for neutrinoless double beta () decay in
Xe with a target half-life sensitivity of approximately years
using kg of isotopically enriched liquid-xenon in a time
projection chamber. This improvement of two orders of magnitude in sensitivity
over current limits is obtained by a significant increase of the Xe
mass, the monolithic and homogeneous configuration of the active medium, and
the multi-parameter measurements of the interactions enabled by the time
projection chamber. The detector concept and anticipated performance are
presented based upon demonstrated realizable background rates.Comment: v2 as publishe
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