5,546 research outputs found
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
Quiet Sun Magnetic Field Measurements Based on Lines with Hyperfine Structure
The Zeeman pattern of MnI lines is sensitive to hyperfine structure (HFS)
and, they respond to hG magnetic field strengths differently from the lines
used in solar magnetometry. This peculiarity has been employed to measure
magnetic field strengths in quiet Sun regions. However, the methods applied so
far assume the magnetic field to be constant in the resolution element. The
assumption is clearly insufficient to describe the complex quiet Sun magnetic
fields, biasing the results of the measurements. We present the first syntheses
of MnI lines in realistic quiet Sun model atmospheres. The syntheses show how
the MnI lines weaken with increasing field strength. In particular, kG magnetic
concentrations produce NnI 5538 circular polarization signals (Stokes V) which
can be up to two orders of magnitude smaller than the weak magnetic field
approximation prediction. Consequently, (1) the polarization emerging from an
atmosphere having weak and strong fields is biased towards the weak fields, and
(2) HFS features characteristic of weak fields show up even when the magnetic
flux and energy are dominated by kG fields. For the HFS feature of MnI 5538 to
disappear the filling factor of kG fields has to be larger than the filling
factor of sub-kG fields. Stokes V depends on magnetic field inclination
according to the simple consine law. Atmospheres with unresolved velocities
produce asymmetric line profiles, which cannot be reproduced by simple
one-component model atmospheres. The uncertainty of the HFS constants do not
limit the use of MnI lines for magnetometry.Comment: Accepted for publication in ApJ. 10 pages, 14 figure
Prominence plasma diagnostics through EUV absorption
In this paper we introduce a new diagnostic technique that uses prominence
EUV and UV absorption to determine the prominence plasma electron temperature
and column emission measure, as well as He/H relative abundance; if a realistic
assumption on the geometry of the absorbing plasma can be made, this technique
can also yield the absorbing plasma electron density. This technique
capitalizes on the absorption properties of Hydrogen and Helium at different
wavelength ranges and temperature regimes. Several cases where this technique
can be successfully applied are described. This technique works best when
prominence plasmas are hotter than 15,000 K and thus it is ideally suited for
rapidly heating erupting prominences observed during the initial phases of
coronal mass ejections. An example is made using simulated intensities of 4
channels of the SDO/AIA instrument. This technique can be easily applied to
existing observations from almost all space missions devoted to the study of
the solar atmosphere, which we list.Comment: 17 pages, 4 figures, submitted to Ap
Signatures of Incomplete Paschen-Back Splitting in the Polarization Profiles of the He I 10830 multiplet
We investigate the formation of polarization profiles induced by a magnetic
field in the He I multiplet at 1083,0 nm . Our analysis considers the Zeeman
splitting in the incomplete Paschen-Back regime. The effects turn out to be
important and produce measurable signatures on the profiles, even for fields
significantly weaker than the level-crossing field (400 G). When compared
to profiles calculated with the usual linear Zeeman effect, the incomplete
Paschen-Back profiles exhibit the following conspicuous differences: a) a
non-Doppler blueshift of the Stokes V zero-crossing wavelength of the blue
component; b) area and peak asymmetries, even in the absence of velocity and
magnetic gradients; c) a 25% reduction in the amplitude of the red
component. These features do not vanish in the weak field limit. The spectral
signatures that we analyze in this paper may be found in previous observations
published in the literature.Comment: Accepted for publication in The Astrophysical Journa
Polynomial Approximants for the Calculation of Polarization Profiles in the \ion{He}{1} 10830 \AA Multiplet
The \ion{He}{1} multiplet at 10830 \AA is formed in the incomplete
Paschen-Back regime for typical conditions found in solar and stellar
atmospheres. The positions and strengths of the various components that form
the Zeeman structure of this multiplet in the Paschen-Back regime are
approximated here by polynomials. The fitting errors are smaller than
m\AA in the component positions and in the relative
strengths. The approximant polynomials allow for a very fast implementation of
the incomplete Paschen-Back regime in numerical codes for the synthesis and
inversion of polarization profiles in this important multiplet.Comment: ApJ Supplements (in press
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