5,916 research outputs found
Ion Temperatures in the Low Solar Corona: Polar Coronal Holes at Solar Minimum
In the present work we use a deep-exposure spectrum taken by the SUMER
spectrometer in a polar coronal hole in 1996 to measure the ion temperatures of
a large number of ions at many different heights above the limb between 0.03
and 0.17 solar radii. We find that the measured ion temperatures are almost
always larger than the electron temperatures and exhibit a non-monotonic
dependence on the charge-to-mass ratio. We use these measurements to provide
empirical constraints to a theoretical model of ion heating and acceleration
based on gradually replenished ion-cyclotron waves. We compare the wave power
required to heat the ions to the observed levels to a prediction based on a
model of anisotropic magnetohydrodynamic turbulence. We find that the empirical
heating model and the turbulent cascade model agree with one another, and
explain the measured ion temperatures, for charge-to-mass ratios smaller than
about 0.25. However, ions with charge-to-mass ratios exceeding 0.25 disagree
with the model; the wave power they require to be heated to the measured ion
temperatures shows an increase with charge-to-mass ratio (i.e., with increasing
frequency) that cannot be explained by a traditional cascade model. We discuss
possible additional processes that might be responsible for the inferred
surplus of wave power.Comment: 11 pages (emulateapj style), 10 figures, ApJ, in press (v. 691,
January 20, 2009
Practical Statistics for the LHC
This document is a pedagogical introduction to statistics for particle
physics. Emphasis is placed on the terminology, concepts, and methods being
used at the Large Hadron Collider. The document addresses both the statistical
tests applied to a model of the data and the modeling itself.Comment: presented at the 2011 European School of High-Energy Physics, Cheile
Gradistei, Romania, 7-20 September 2011 I expect to release updated versions
of this document in the futur
Statistical Challenges for Searches for New Physics at the LHC
Because the emphasis of the LHC is on 5 sigma discoveries and the LHC
environment induces high systematic errors, many of the common statistical
procedures used in High Energy Physics are not adequate. I review the basic
ingredients of LHC searches, the sources of systematics, and the performance of
several methods. Finally, I indicate the methods that seem most promising for
the LHC and areas that are in need of further study.Comment: 12 pages, 7 figures, proceedings of PhyStat2005, Oxford. To be
published by Imperial College Press. See
http://www.physics.ox.ac.uk/phystat05/index.ht
Frequentist Hypothesis Testing with Background Uncertainty
We consider the standard Neyman-Pearson hypothesis test of a
signal-plus-background hypothesis and background-only hypothesis in the
presence of uncertainty on the background-only prediction. Surprisingly, this
problem has not been addressed in the recent conferences on statistical
techniques in high-energy physics -- although the its confidence-interval
equivalent has been. We discuss the issues of power, similar tests, coverage,
and ordering rules. The method presented is compared to the Cousins-Highland
technique, the ratio of Poisson means, and ``profile'' method.Comment: Talk from PhyStat2003, Stanford, Ca, USA, September 2003, 4 pages,
LaTeX, 2 eps figures. PSN WEMT00
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