541 research outputs found
A Markov Chain Monte Carlo technique to sample transport and source parameters of Galactic cosmic rays: II. Results for the diffusion model combining B/C and radioactive nuclei
On-going measurements of the cosmic radiation (nuclear, electronic, and
gamma-ray) are shedding new light on cosmic-ray physics. A comprehensive
picture of these data relies on an accurate determination of the transport and
source parameters of propagation models. A Markov Chain Monte Carlo is used to
obtain these parameters in a diffusion model. From the measurement of the B/C
ratio and radioactive cosmic-ray clocks, we calculate their probability density
functions, with a special emphasis on the halo size L of the Galaxy and the
local underdense bubble of size r_h. The analysis relies on the USINE code for
propagation and on a Markov Chain Monte Carlo technique (Putze et al. 2009,
paper I of this series) for the parameter determination. As found in previous
studies, the B/C best-fit model favours diffusion/convection/reacceleration
(Model III) over diffusion/reacceleration (Model II). A combined fit on B/C and
the isotopic ratios (10Be/9Be, 26Al/27Al, 36Cl/Cl) leads to L ~ 8 kpc and r_h ~
120 pc for the best-fit Model III. This value for r_h is consistent with direct
measurements of the local interstallar medium. For Model II, L ~ 4 kpc and r_h
is consistent with zero. We showed the potential and usefulness of the Markov
Chain Monte Carlo technique in the analysis of cosmic-ray measurements in
diffusion models. The size of the diffusive halo depends crucially on the value
of the diffusion slope delta, and also on the presence/absence of the local
underdensity damping effect on radioactive nuclei. More precise data from
on-going experiments are expected to clarify this issue.Comment: 20 pages, 14 figures, minor language corrections to match the A&A
accepted versio
Nuclear Cosmic Rays propagation in the Atmosphere
The transport of the nuclear cosmic ray flux in the atmosphere is studied and
the atmospheric corrections to be applied to the measurements are calculated.
The contribution of the calculated corrections to the accuracy of the
experimental results are discussed and evaluated over the kinetic energy range
10-10 GeV/n. The Boron (B) and Carbon (C) elements system is used as a
test case. It is shown that the required corrections become largely dominant at
the highest energies investigated. The results are discussed.Comment: Proc. of 30th International Cosmic Ray Conference, Merida, Mexico; 4
page
Neutron monitors and muon detectors for solar modulation studies: Interstellar flux, yield function, and assessment of critical parameters in count rate calculations
Particles count rates at given Earth location and altitude result from the
convolution of (i) the interstellar (IS) cosmic-ray fluxes outside the solar
cavity, (ii) the time-dependent modulation of IS into Top-of-Atmosphere (TOA)
fluxes, (iii) the rigidity cut-off (or geomagnetic transmission function) and
grammage at the counter location, (iv) the atmosphere response to incoming TOA
cosmic rays (shower development), and (v) the counter response to the various
particles/energies in the shower. Count rates from neutron monitors or muon
counters are therefore a proxy to solar activity. In this paper, we review all
ingredients, discuss how their uncertainties impact count rate calculations,
and how they translate into variation/uncertainties on the level of solar
modulation (in the simple Force-Field approximation). The main
uncertainty for neutron monitors is related to the yield function. However,
many other effects have a significant impact, at the 5-10\% level on
values. We find no clear ranking of the dominant effects, as some depend on the
station position and/or the weather and/or the season. An abacus to translate
any variation of count rates (for neutron and detectors) to a variation
of the solar modulation is provided.Comment: 28 pages, 16 figures, 9 tables, match accepted version in AdSR (minor
corrections, Dorman (1974,2004,2009) reference textbooks added
Neutron monitors and muon detectors for solar modulation studies: 2. time series
The level of solar modulation at different times (related to the solar
activity) is a central question of solar and galactic cosmic-ray physics. In
the first paper of this series, we have established a correspondence between
the uncertainties on ground-based detectors count rates and the parameter
(modulation level in the force-field approximation) reconstructed from
these count rates. In this second paper, we detail a procedure to obtain a
reference time series from neutron monitor data. We show that we can
have an unbiased and accurate reconstruction (). We also discuss the potential of Bonner spheres spectrometers and muon
detectors to provide time series. Two by-products of this calculation
are updated values for the cosmic-ray database and a web interface to
retrieve and plot from the 50's to today
(\url{http://lpsc.in2p3.fr/crdb}).Comment: 15 pages, 5 figures, 2 tables. AdSR, in press. Web interface to get
modulation parameter phi(t): new tab in http://lpsc.in2p3.fr/crd
Transport parameters from AMS-02 F/Si data and fluorine source abundance
The AMS-02 collaboration recently released cosmic-ray F/Si data of
unprecedented accuracy. CR F is predominantly produced by fragmentation of
heavier progenitors, while Si is mostly accelerated at source. This ratio is
thus maximally sensitive to CR propagation. We study the compatibility of the
transport parameters derived from the F/Si ratio with those obtained from the
lighter Li/C, Be/C, and B/C ratios. We also inspect the CR source abundance of
F, one of the few elements with a high first ionisation potential but only
moderately volatile, and a potentially key element to study the acceleration
mechanism of CRs. We use the 1D diffusion model implemented in the USINE code
and perform analyses accounting for several systematic effects (energy
correlations in data, nuclear cross sections and solar modulation
uncertainties). We also take advantage of the EXFOR nuclear database to update
the F production cross sections for its most important progenitors (identified
to be 56Fe, 32S, 28Si, 27Al, 24Mg, 22Ne, and 20Ne). The transport parameters
obtained from AMS-02 F/Si data are compatible with those obtained from AMS-02
(Li,Be,B)/C data. The combined fit of all these ratios leads to a
, with adjustments of the B and F
production cross sections (the latter are based on very few nuclear data
points, and would strongly benefit from new measurements). The F/Si ratio is
compatible with a pure secondary origin of F, with a best-fit relative source
abundance 19F/28Si and an upper limit of . Unfortunately, this limit is not sufficient to test global
acceleration models of CR nuclei, for which values at the level of are required. Such levels could be attained with F/Si data of a few
percent accuracy at a few tens of TV, possibly within reach of the next
generation of CR experiments.Comment: 15 pages, 13 figures, 3 table (1 appendix). Submitted to A&
Atmospheric neutrino flux from 3-dimensional simulation
The atmospheric muon and neutrino flux have been simulated using the same
approach which successfully accounted for the recent secondary proton, electron
and positron flux measurements in orbit by the AMS experiment. For the muon
flux, a good agreement is obtained with the CAPRICE and HEAT data for altitudes
ranging from sea level up to about 38 km. The general features of the
calculated atmospheric neutrino flux are reported and discussed. The flux
obtained at the Super-Kamiokande experiment location are reported and compared
with other calculations. For low neutrino energies the flux obtained is
significantly smaller than that used in the data analysis of underground
experiment. The simulation results for the SOUDAN experiment site are also
reported.Comment: 33 pages, 27 figures, 12 tables, final version for Phys. Rev.
Design and construction of a Cherenkov imager for charge measurement of nuclear cosmic rays
A proximity focusing Cherenkov imager called CHERCAM, has been built for the
charge measurement of nuclear cosmic rays with the CREAM instrument. It
consists of a silica aerogel radiator plane across from a detector plane
equipped with 1,600 1" diameter photomultipliers. The two planes are separated
by a ring expansion gap. The Cherenkov light yield is proportional to the
charge squared of the incident particle. The expected relative light collection
accuracy is in the few percents range. It leads to an expected single element
separation over the range of nuclear charge Z of main interest 1 < Z < 26.
CHERCAM is designed to fly with the CREAM balloon experiment. The design of the
instrument and the implemented technical solutions allowing its safe operation
in high altitude conditions (radiations, low pressure, cold) are presented.Comment: 24 pages, 19 figure
AMS-02 antiprotons and dark matter: Trimmed hints and robust bounds
Based on 4 yr AMS-02 antiproton data, we present bounds on the dark matter
(DM) annihilation cross section vs. mass for some representative final state
channels. We use recent cosmic-ray propagation models, a realistic treatment of
experimental and theoretical errors, and an updated calculation of input
antiproton spectra based on a recent release of the PYTHIA code. We find that
reported hints of a DM signal are statistically insignificant; an adequate
treatment of errors is crucial for credible conclusions. Antiproton bounds on
DM annihilation are among the most stringent ones, probing thermal DM up to the
TeV scale. The dependence of the bounds upon propagation models and the DM halo
profile is also quantified. A preliminary estimate reaches similar conclusions
when applied to the 7 years AMS-02 dataset, but also suggests extra caution as
for possible future claims of DM excesses.Comment: v2: 33 pages, 6 figures (two of which in two panels); clarifications
and a couple of references added, conclusions unchange
The rigidity dependence of galactic cosmic-ray fluxes and its connection with the diffusion coefficient
Thanks to tremendous experimental efforts, galactic cosmic-ray fluxes are being measured up to the unprecedented per cent precision level. The logarithmic slope of these fluxes is a crucial quantity that promises us information on the diffusion properties and the primary or secondary nature of the different species. However, these measured slopes are sometimes interpreted in the pure diffusive regime, guiding to misleading conclusions. In this paper, we have studied the propagation of galactic cosmic rays by computing the fluxes of species between H and Fe using the USINE code and considering all the relevant physical processes and an updated set of cross-section data. We show that the slope of the well-studied secondary-to-primary B/C ratio is distinctly different from the diffusion coefficient slope, by an offset of about 0.2 in the rigidity range in which the AMS-02 data reach their best precision (several tens of GV). Furthermore, we have demonstrated that none of the species from H to Fe follows the expectations of the pure-diffusive regime. We argue that these differences arise from propagation processes such as fragmentation, convection, and reacceleration, which cannot be neglected. On this basis, we also provide predictions for the spectral slope of elemental fluxes not yet analysed by the AMS collaboration
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