233,136 research outputs found
CDF Hot Topics
We present recent CDF results based on approximately 1 fb of
collisions at TeV delivered at Fermilab Tevatron. Results
shown include the observation of the oscillation frequency, the first
observation of bottom baryon states, updates on hadrons
lifetimes, and searches for rare decays in the transition
and in charmless two-body B decays.Comment: Flavor Physics & CP Violation Conference, Bled, 200
Superbeams versus Neutrino Factories
We compare the physics potential of planned superbeams with the one of
neutrino factories. Therefore, the experimental setups as well as the most
relevant uncertainties and errors are considered on the same footing as much as
possible. We use an improved analysis including the full parameter
correlations, as well as statistical, systematical, and degeneracy errors.
Especially, degeneracies have so far not been taken into account in a numerical
analysis. We furthermore include external input, such as improved knowledge of
the solar oscillation parameters from the KamLAND experiment. This allows us to
determine the limiting uncertainties in all cases. For a specific comparison,
we choose two representatives of each class: For the superbeam, we take the
first conceivable setup, namely the JHF to SuperKamiokande experiment, as well
as, on a longer time scale, the JHF to HyperKamiokande experiment. For the
neutrino factory, we choose an initially conceivable setup and an advanced
machine. We determine the potential to measure the small mixing angle sin^2 2
theta_{13}, the sign of Delta m^2_{31}, and the leptonic CP phase \deltacp,
which also implies that we compare the limitations of the different setups. We
find interesting results, such as the complete loss of the sensitivity to the
sign of Delta m^2_{31} due to degeneracies in many cases.Comment: Revised version with JHF energy resolution corrected, discussion of
detector issues added (App. B), and references added. Summary and conclusions
unchanged. 51 pages, 28 figures, 4 table
Optimizing momentum resolution with a new fitting method for silicon-strip detectors
A new fitting method is explored for momentum reconstruction of tracks in a
constant magnetic field for a silicon-strip tracker. Substantial increases of
momentum resolution respect to standard fit is obtained. The key point is the
use of a realistic probability distribution for each hit (heteroscedasticity).
Two different methods are used for the fits, the first method introduces an
effective variance for each hit, the second method implements the maximum
likelihood search. The tracker model is similar to the PAMELA tracker. Each
side, of the two sided of the PAMELA detectors, is simulated as momentum
reconstruction device. One of the two is similar to silicon micro-strip
detectors of large use in running experiments. Two different position
reconstructions are used for the standard fits, the -algorithm (the best
one) and the two-strip center of gravity. The gain obtained in momentum
resolution is measured as the virtual magnetic field and the virtual
signal-to-noise ratio required by the two standard fits to reach an overlap
with the best of two new methods. For the best side, the virtual magnetic field
must be increased 1.5 times respect to the real field to reach the overlap and
1.8 for the other. For the high noise side, the increases must be 1.8 and 2.0.
The signal-to-noise ratio has similar increases but only for the
-algorithm. The signal-to-noise ratio has no effect on the fits with the
center of gravity. Very important results are obtained if the number N of
detecting layers is increased, our methods provide a momentum resolution
growing linearly with N, much higher than standard fits that grow as the
.Comment: This article supersedes arXiv:1606.03051, 22 pages and 10 figure
B Physics at the Tevatron: Run II and Beyond
This report provides a comprehensive overview of the prospects for B physics
at the Tevatron. The work was carried out during a series of workshops starting
in September 1999. There were four working groups: 1) CP Violation, 2) Rare and
Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and
Spectroscopy. The report also includes introductory chapters on theoretical and
experimental tools emphasizing aspects of B physics specific to hadron
colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a
Summary.Comment: 583 pages. Further information on the workshops, including
transparencies, can be found at the workshop's homepage:
http://www-theory.lbl.gov/Brun2/. The report is also available in 2-up
http://www-theory.lbl.gov/Brun2/report/report2.ps.gz or chapter-by-chapter
http://www-theory.lbl.gov/Brun2/report
Fundamental limitations of high contrast imaging set by small sample statistics
In this paper, we review the impact of small sample statistics on detection
thresholds and corresponding confidence levels (CLs) in high contrast imaging
at small angles. When looking close to the star, the number of resolution
elements decreases rapidly towards small angles. This reduction of the number
of degrees of freedom dramatically affects CLs and false alarm probabilities.
Naively using the same ideal hypothesis and methods as for larger separations,
which are well understood and commonly assume Gaussian noise, can yield up to
one order of magnitude error in contrast estimations at fixed CL. The
statistical penalty exponentially increases towards very small inner working
angles. Even at 5-10 resolution elements from the star, false alarm
probabilities can be significantly higher than expected. Here we present a
rigorous statistical analysis which ensures robustness of the CL, but also
imposes a substantial limitation on corresponding achievable detection limits
(thus contrast) at small angles. This unavoidable fundamental statistical
effect has a significant impact on current coronagraphic and future high
contrast imagers. Finally, the paper concludes with practical recommendations
to account for small number statistics when computing the sensitivity to
companions at small angles and when exploiting the results of direct imaging
planet surveys.Comment: 12 pages, 10 figures, accepted to Ap
Recommended from our members
A content-aware quantisation mechanism for transform domain distributed video coding
The discrete cosine transform (DCT) is widely applied in modern codecs to remove spatial redundancies, with the resulting DCT coefficients being quantised to achieve compression as well as bit-rate control. In distributed video coding (DVC) architectures like DISCOVER, DCT coefficient quantisation is traditionally performed using predetermined quantisation matrices (QM), which means the compression is heavily dependent on the sequence being coded. This makes bit-rate control challenging, with the situation exacerbated in the coding of high resolution sequences due to QM scarcity and the non-uniform bit-rate gaps between them. This paper introduces a novel content-aware quantisation (CAQ) mechanism to overcome the limitations of existing quantisation methods in transform domain DVC. CAQ creates a frame-specific QM to reduce quantisation errors by analysing the distribution of DCT coefficients. In contrast to the predetermined QM that is applicable to only 4x4 block sizes, CAQ produces QM for larger block sizes to enhance compression at higher resolutions. This provides superior bit-rate control and better output quality by seeking to fully exploit the available bandwidth, which is especially beneficial in bandwidth constrained scenarios. In addition, CAQ generates superior perceptual results by innovatively applying different weightings to the DCT coefficients to reflect the human visual system. Experimental results corroborate that CAQ both quantitatively and qualitatively provides enhanced output quality in bandwidth limited scenarios, by consistently utilising over 90% of available bandwidth
Fundamental Imaging Limits of Radio Telescope Arrays
The fidelity of radio astronomical images is generally assessed by practical
experience, i.e. using rules of thumb, although some aspects and cases have
been treated rigorously. In this paper we present a mathematical framework
capable of describing the fundamental limits of radio astronomical imaging
problems. Although the data model assumes a single snapshot observation, i.e.
variations in time and frequency are not considered, this framework is
sufficiently general to allow extension to synthesis observations. Using tools
from statistical signal processing and linear algebra, we discuss the
tractability of the imaging and deconvolution problem, the redistribution of
noise in the map by the imaging and deconvolution process, the covariance of
the image values due to propagation of calibration errors and thermal noise and
the upper limit on the number of sources tractable by self calibration. The
combination of covariance of the image values and the number of tractable
sources determines the effective noise floor achievable in the imaging process.
The effective noise provides a better figure of merit than dynamic range since
it includes the spatial variations of the noise. Our results provide handles
for improving the imaging performance by design of the array.Comment: 12 pages, 8 figure
Neutrino Beams From Electron Capture at High Gamma
We investigate the potential of a flavor pure high gamma electron capture
electron neutrino beam directed towards a large water cherenkov detector with
500 kt fiducial mass. The energy of the neutrinos is reconstructed by the
position measurement within the detector and superb energy resolution
capabilities could be achieved. We estimate the requirements for such a
scenario to be competitive to a neutrino/anti-neutrino running at a neutrino
factory with less accurate energy resolution. Although the requirements turn
out to be extreme, in principle such a scenario could achieve as good abilities
to resolve correlations and degeneracies in the search for sin^2(2 theta_13)
and delta_CP as a standard neutrino factory experiment.Comment: 21 pages, 7 figures, revised version, to appear in JHEP, Fig.7
extended, minnor changes, results unchange
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