200 research outputs found
Thin-disk laser pump schemes for large number of passes and moderate pump source quality
Novel thin-disk laser pump layouts are proposed yielding an increased number
of passes for a given pump module size and pump source quality. These novel
layouts result from a general scheme which bases on merging two simpler pump
optics arrangements. Some peculiar examples can be realized by adapting
standard commercially available pump optics simply by intro ducing an
additional mirror-pair. More pump passes yield better efficiency, opening the
way for usage of active materials with low absorption. In a standard multi-pass
pump design, scaling of the number of beam passes brings ab out an increase of
the overall size of the optical arrangement or an increase of the pump source
quality requirements. Such increases are minimized in our scheme, making them
eligible for industrial applicationsComment: 16 pages, 9 figure
muCool: A novel low-energy muon beam for future precision experiments
Experiments with muons () and muonium atoms () offer
several promising possibilities for testing fundamental symmetries. Examples of
such experiments include search for muon electric dipole moment, measurement of
muon and experiments with muonium from laser spectroscopy to gravity
experiments. These experiments require high quality muon beams with small
transverse size and high intensity at low energy.
At the Paul Scherrer Institute, Switzerland, we are developing a novel device
that reduces the phase space of a standard beam by a factor of
with efficiency. The phase space compression is achieved by
stopping a standard beam in a cryogenic helium gas. The stopped
are manipulated into a small spot with complex electric and magnetic
fields in combination with gas density gradients. From here, the muons are
extracted into the vacuum and into a field-free region. Various aspects of this
compression scheme have been demonstrated. In this article the current status
will be reported.Comment: 8 pages, 5 figures, TCP 2018 conference proceeding
Muonic hydrogen cascade time and lifetime of the short-lived state
Metastable muonic-hydrogen atoms undergo collisional -quenching,
with rates which depend strongly on whether the kinetic energy is above
or below the energy threshold. Above threshold, collisional
excitation followed by fast radiative
deexcitation is allowed. The corresponding short-lived component
was measured at 0.6 hPa room temperature gas pressure, with
lifetime ns (i.e.,
at liquid-hydrogen density) and population
% (per atom). In
addition, a value of the cascade time, ns, was found.Comment: 4 pages, 3 figure
SN 2010jl in UGC 5189: Yet another luminous type IIn supernova in a metal-poor galaxy
We present ASAS data starting 25 days before the discovery of the recent type
IIn SN 2010jl, and we compare its light curve to other luminous IIn SNe,
showing that it is a luminous (M_I ~ -20.5) event. Its host galaxy, UGC 5189,
has a low gas-phase oxygen abundance (12 + log(O/H) = 8.2), which reinforces
the emerging trend that over-luminous core-collapse supernovae are found in the
low-metallicity tail of the galaxy distribution, similar to the known trend for
the hosts of long GRBs. We compile oxygen abundances from the literature and
from our own observations of UGC 5189, and we present an unpublished spectrum
of the luminous type Ic SN 2010gx that we use to estimate its host metallicity.
We discuss these in the context of host metallicity trends for different
classes of core-collapse objects. The earliest generations of stars are known
to be enhanced in [O/Fe] relative to the Solar mixture; it is therefore likely
that the stellar progenitors of these overluminous supernovae are even more
iron-poor than they are oxygen-poor. A number of mechanisms and massive star
progenitor systems have been proposed to explain the most luminous
core-collapse supernovae; any successful theory will need to include the
emerging trend that points towards low-metallicity for the massive progenitor
stars. This trend for very luminous supernovae to strongly prefer
low-metallicity galaxies should be taken into account when considering various
aspects of the evolution of the metal-poor early universe. (abridged)Comment: 27 pages, 7 figures, 2 tables. Accepted for publication in Ap
The proton radius puzzle
High-precision measurements of the proton radius from laser spectroscopy of
muonic hydrogen demonstrated up to six standard deviations smaller values than
obtained from electron-proton scattering and hydrogen spectroscopy. The status
of this discrepancy, which is known as the proton radius puzzle will be
discussed in this paper, complemented with the new insights obtained from
spectroscopy of muonic deuterium.Comment: Moriond 2017 conference, 8 pages, 4 figure
Improved X-ray detection and particle identification with avalanche photodiodes
Avalanche photodiodes are commonly used as detectors for low energy x-rays.
In this work we report on a fitting technique used to account for different
detector responses resulting from photo absorption in the various APD layers.
The use of this technique results in an improvement of the energy resolution at
8.2 keV by up to a factor of 2, and corrects the timing information by up to 25
ns to account for space dependent electron drift time. In addition, this
waveform analysis is used for particle identification, e.g. to distinguish
between x-rays and MeV electrons in our experiment.Comment: 6 pages, 6 figure
Muon Physics: A Pillar of the Standard Model
Since its discovery in the 1930s, the muon has played an important role in
our quest to understand the sub-atomic theory of matter. The muon was the first
second-generation standard-model particle to be discovered, and its decay has
provided information on the (Vector -Axial Vector) structure of the weak
interaction, the strength of the weak interaction, G_F, and the conservation of
lepton number (flavor) in muon decay. The muon's anomalous magnetic moment has
played an important role in restricting theories of physics beyond the standard
standard model, where at present there is a 3.4 standard-deviation difference
between the experiment and standard-model theory. Its capture on the atomic
nucleus has provided valuable information on the modification of the weak
current by the strong interaction which is complementary to that obtained from
nuclear beta decay.Comment: 8 pages, 9 figures. Invited paper for the Journal of Physical Society
in Japan (JPSJ), Special Topics Issue "Frontiers of Elementary Particle
Physics, The Standard Model and beyond
Optimal design for correlated processes with input-dependent noise
Optimal design for parameter estimation in Gaussian process regression models with input-dependent noise is examined. The motivation stems from the area of computer experiments, where computationally demanding simulators are approximated using Gaussian process emulators to act as statistical surrogates. In the case of stochastic simulators, which produce a random output for a given set of model inputs, repeated evaluations are useful, supporting the use of replicate observations in the experimental design. The findings are also applicable to the wider context of experimental design for Gaussian process regression and kriging. Designs are proposed with the aim of minimising the variance of the Gaussian process parameter estimates. A heteroscedastic Gaussian process model is presented which allows for an experimental design technique based on an extension of Fisher information to heteroscedastic models. It is empirically shown that the error of the approximation of the parameter variance by the inverse of the Fisher information is reduced as the number of replicated points is increased. Through a series of simulation experiments on both synthetic data and a systems biology stochastic simulator, optimal designs with replicate observations are shown to outperform space-filling designs both with and without replicate observations. Guidance is provided on best practice for optimal experimental design for stochastic response models
Characterization of large area avalanche photodiodes in X-ray and VUV-light detection
The present manuscript reviews our R+D studies on the application of large area avalanche photodiodes (LAAPDs) to the detection of X-rays and vacuum ultraviolet (VUV) light. The operational characteristics of LAAPDs manufactured by Advanced Photonix Inc. were investigated for X-ray detection at room temperature. The optimum energy resolution obtained in four LAAPDs investigated was found to be in the range 10-18% for 5.9 keV X-rays. The observed variations are associated with dark current differences between the several prototypes. LAAPDs have demonstrated high counting rate capability (up to about 10â”/s) and applicability in diverse areas, mainly low-energy X-ray detection, where LAAPDs selected for low dark current may achieve better performance than proportional counters. LAAPDs were also investigated as VUV photosensors, presenting advantages compared to photomultiplier tubes. X-rays are often used as a reference in light measurements; this may be compromised by the non-linearity between gains measured for X-rays and VUV-light. The gain was found to be lower for X-rays than for VUV light, especially at higher bias voltages. For 5.9 keV X-rays, gain variations of 10% and 6% were measured relative to VUV light produced in argon ( ⌠128 nm) and xenon ( ⌠172 nm) for gains of about 200. The effect of temperature on the LAAPD performance was investigated for X-ray and VUV-light detection. Gain variations of more than -4% per oC were measured for 5.9 keV X-rays for gains above 200, while for VUV light variations are larger than -5% per oC. The energy resolution was found to improve with decreasing temperature, what is mainly attributed to dark current. The excess noise factor, another contribution to the energy resolution, was experimentally determined and found to be independent of temperature, increasing linearly with gain, from 1.8 to 2.3 for a 50-300 gain range. The LAAPD response under intense magnetic fields up to 5 Tesla was investigated. While for X-ray detection the APD response practically does not vary with the magnetic field, for 172 nm VUV light a significant amplitude reduction of more than 20% was observed
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