21,274 research outputs found
QED Interconnection Effects on W Momentum Distributions at LEP 2
The process \ee \to \W^+\W^- \to \f_1 \fbar_2 \, \f_3 \fbar_4 contains
charges in the initial, intermediate and final stages. This gives a rich
selection of possible QED interconnection effects. Coulomb interaction is the
simplest of these, and can thus be used to explore consequences. We study a
number of experimental observables, with emphasis on those related to the W
momentum distribution. Second-order Coulomb effects are shown to be practically
negligible. The limited LEP~2 statistics will not allow detailed tests, so any
theory uncertainty will be reflected in the systematic error on the W mass.
Currently the uncertainty from this source may be as high as 20~MeV.Comment: 1+27 pages, including 23 eps figures, use uudecode and gunzip to
restore original file, run LaTeX2epsilon with epsfig package, figures are
included in filecontents environments; alternatively ready-made postscript
file is available at http://thep.lu.se/tf2/staff/torbjorn/Welcome.htm
Self-Calibration of Neutrino Detectors using characteristic Backgrounds
We introduce the possibility to use characteristic natural neutrino
backgrounds, such as Geoneutrinos (\bar{\nu}_e) or solar neutrinos (\nu_e),
with known spectral shape for the energy calibration of future neutrino
detectors, e.g. Large Liquid Scintillator Detectors. This "CalEffect" could be
used without the need to apply any modifications to the experiment in all
situations where one has a suitable background with sufficient statistics.
After deriving the effect analytically using \chi^2 statistics, we show that it
is only tiny for reactor neutrino experiments, but can be applicable in other
situations. As an example, we present its impact on the identification of the
wiggles in the power spectrum of supernova neutrinos caused by Earth matter
effects. The Self-Calibration Effect could be used for cross checking other
calibration methods and to resolve systematical effects in the primary neutrino
interaction processes, in particular in the low energy cross sections.Comment: 6 pages, 4 figure
On the use of C-stat in testing models for X-ray spectra
It has been shown that for the analysis of X-ray spectra the C-statistic,
contrary to the chi^2-statistic, provides unbiased estimates of the model
parameters and their uncertainty ranges. However, it is often stated that the
C-statistic cannot be used to carry out statistical tests on the goodness of
fit of the model, and therefore several investigations are still based on
chi^2-statistics. Here we show that it is straightforward to calculate the
expected value and variance of the C-statistic so that it can be used in tests.
We provide formulae and simple numerical approximations to evaluate these
expected values and variances. We also give examples indicating that tests
based on only the expected value and variance of the C-statistic are reliable
for spectra even with only ~30 counts. Therefore the C-statistic can be used
for statistical tests such as assessing the goodness of fit of a spectral
model.Comment: 4 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
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