242 research outputs found
A model independent safeguard for unbinned Likelihood
We present a universal method to include residual un-modeled background shape
uncertainties in likelihood based statistical tests for high energy physics and
astroparticle physics. This approach provides a simple and natural protection
against mismodeling, thus lowering the chances of a false discovery or of an
over constrained confidence interval, and allows a natural transition to
unbinned space. Unbinned likelihood allows optimal usage of information for the
data and the models, and enhances the sensitivity.
We show that the asymptotic behavior of the test statistic can be regained in
cases where the model fails to describe the true background behavior, and
present 1D and 2D case studies for model-driven and data-driven background
models. The resulting penalty on sensitivities follows the actual discrepancy
between the data and the models, and is asymptotically reduced to zero with
increasing knowledge
From Final Dark Matter Results and Background Shape Uncertainties in XENON100 to First Light in XENON1T
The quest to directly detect dark matter, in particular weakly interactive massive particles (WIMP), lead to a development of a plethora of detector technologies. Since 2007 dual-phase time-projection chambers exploiting liquid xenon performed superior to all other technologies at WIMP masses above a few GeV/c^2. Among them, the XENON100 experiment shows the longest measurement with a combined live time of 477 days. An analysis to probe spin independent and spin dependent WIMP interactions is presented in this thesis, setting an upper limit on the WIMP-nucleon spin independent cross section at 1.1Ă10â45 cm^2 for a 50 GeV/c^2 WIMP mass. Furthermore, potential improvements are identified in the conventional XENON100 analysis and the outlined solution allows to consider shape uncertainties of non-parametric probability density functions by means of a profile likelihood analysis. The applicability of the method is shown by constraining the WIMP model in an astrophysical independent approach with XENON100 data. Finally, performance tests of the Hamamatsu R11410-21 3â photomultiplier tubes (PMT) are presented which are employed in the next generation experiment XENON1T. First results from the commissioning of the XENON1T detector with respect to the PMT performance are shown with a special focus on the impact of light emitting tubes
Detection of Xe from the Fukushima nuclear power plant in the upper troposphere above Germany
After the accident in the Japanese Fukushima Dai-ichi nuclear power plant in
March 2011 large amounts of radioactivity were released and distributed in the
atmosphere. Among them were also radioactive noble gas isotopes which can be
used as tracers to test global atmospheric circulation models. This work
presents unique measurements of the radionuclide Xe from Fukushima in
the upper troposphere above Germany. The measurements involve air sampling in a
research jet aircraft followed by chromatographic xenon extraction and
ultra-low background gas counting with miniaturized proportional counters. With
this technique a detection limit of the order of 100 Xe atoms in
litre-scale air samples (corresponding to about 100 mBq/m) is achievable.
Our results provide proof that the Xe-rich ground level air layer from
Fukushima was lifted up to the tropopause and distributed hemispherically.
Moreover, comparisons with ground level air measurements indicate that the
arrival of the radioactive plume at high altitude over Germany occurred several
days before the ground level plume.Comment: 8 pages, 5 figure
Dynamical Semigroup Description of Coherent and Incoherent Particle-Matter Interaction
The meaning of statistical experiments with single microsystems in quantum
mechanics is discussed and a general model in the framework of non-relativistic
quantum field theory is proposed, to describe both coherent and incoherent
interaction of a single microsystem with matter. Compactly developing the
calculations with superoperators, it is shown that the introduction of a time
scale, linked to irreversibility of the reduced dynamics, directly leads to a
dynamical semigroup expressed in terms of quantities typical of scattering
theory. Its generator consists of two terms, the first linked to a coherent
wavelike behaviour, the second related to an interaction having a measuring
character, possibly connected to events the microsystem produces propagating
inside matter. In case these events breed a measurement, an explicit
realization of some concepts of modern quantum mechanics ("effects" and
"operations") arises. The relevance of this description to a recent debate
questioning the validity of ordinary quantum mechanics to account for such
experimental situations as, e.g., neutron-interferometry, is briefly discussed.Comment: 22 pages, latex, no figure
a retrospective analysis
Purpose: We looked for any predictive value of change in primary tumor and
metastatic lymph node volumes after induction chemotherapy (IC) on oncologic
outcome in head and neck squamous cell carcinoma (HNSCC). Methods: Nineteen
patients with stage IVA/B HNSCC treated between 2004 and 2010 with at least
one cycle of IC (docetaxel, cisplatin and 5-fluorouracil / TPF) and
concomitant chemoradiotherapy (CRT) with cisplatin were retrospectively
analyzed. Volumes were calculated separately for primary tumor (Vtm), lymph
node metastases (Vln) and their sum (Vsum) on computed tomography (CT) images
before and after IC. The effect of volumetric changes on locoregional failure
(LRF), distant metastasis (DM) and overall survival (OS) was assessed. P
values <0.05 were considered as statistically significant. Results: The median
follow-up of surviving patients was 25 months (range: 10.7-83.3). The median
number of cycles and duration of TPF was 3 (range: 1-4) and 44 days (range:
4-116), respectively. Empirical area under the curve (AUC) analyses for death,
LRF and DM revealed optimal cut-off values of Vtm diminution (30.54%, AUC:
87%) and Vsum decrease (35.45%, AUC: 64.55%) only for OS (p <0.05). Among
those, a reduction in Vsum more than 35.4% between pre- and post-IC was
significantly correlated with better OS (100 vs 43% at 2 years, p <0.05).
Conclusion: Volumetric shrinkage of the tumor load after IC assessed with CT
seems to predict OS. The assessment of volumetric shrinkage upon IC might be
used to decide whether to offer patients alternative strategies like
palliative/de-intensified treatments or more aggressive combined modalities
after IC
Optimization viewpoint on Kalman smoothing, with applications to robust and sparse estimation
In this paper, we present the optimization formulation of the Kalman
filtering and smoothing problems, and use this perspective to develop a variety
of extensions and applications. We first formulate classic Kalman smoothing as
a least squares problem, highlight special structure, and show that the classic
filtering and smoothing algorithms are equivalent to a particular algorithm for
solving this problem. Once this equivalence is established, we present
extensions of Kalman smoothing to systems with nonlinear process and
measurement models, systems with linear and nonlinear inequality constraints,
systems with outliers in the measurements or sudden changes in the state, and
systems where the sparsity of the state sequence must be accounted for. All
extensions preserve the computational efficiency of the classic algorithms, and
most of the extensions are illustrated with numerical examples, which are part
of an open source Kalman smoothing Matlab/Octave package.Comment: 46 pages, 11 figure
Cool, Luminous, and Highly Variable Stars in the Magellanic Clouds. II: Spectroscopic and Environmental Analysis of Thorne-\.Zytkow Object and Super-AGB Star Candidates
In previous work we identified a population of 38 cool and luminous variable
stars in the Magellanic Clouds and examined 11 in detail in order to classify
them as either Thorne-\.Zytkow Objects (T\.ZOs, red supergiants with a neutron
star cores) or super-AGB stars (the most massive stars that will not undergo
core collapse). This population includes HV\,2112, a peculiar star previously
considered in other works to be either a T\.ZO or high-mass AGB star. Here we
continue this investigation, using the kinematic and radio environments and
local star formation history of these stars to place constraints on the age of
the progenitor systems and the presence of past supernovae. These stars are not
associated with regions of recent star formation, and we find no evidence of
past supernovae at their locations. Finally, we also assess the presence of
heavy elements and lithium in their spectra compared to red supergiants. We
find strong absorption in Li and s-process elements compared to RSGs in most of
the sample, consistent with super-AGB nucleosynthesis, while HV\,2112 shows
additional strong lines associated with T\.ZO nucleosynthesis. Coupled with our
previous mass estimates, the results are consistent with the stars being
massive (~4-6.5M) or super-AGB (~6.5-12M) stars in the
thermally pulsing phase, providing crucial observations of the transition
between low- and high-mass stellar populations. HV\,2112 is more ambiguous; it
could either be a maximally massive sAGB star, or a T\.ZO if the minimum mass
for stability extends down to <13 M.Comment: 32 pages, 10 figures, 7 tables, spectroscopic data available at
https://zenodo.org/record/7058608, accepted to The Astrophysical Journa
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