896 research outputs found
Inhomogeneous diffusion model for recent data on high-energy cosmic rays
The AMS Collaboration has recently released precision data on cosmic ray (CR)
leptons and protons at high energies. Interesting progresses have also been
made on the measurement of CR nuclei, such as the boron-to-carbon ratio or the
lithium spectrum, up to TeV/nucleon energies. In order to provide a description
these data, I consider a diffusion model of CR propagation which allows for
latitudinal variations of the CR diffusion properties in the Galactic halo. I
discuss the role of high-precision data on light CR nuclei in resolutely
testing this model and the key propagation parameters.Comment: 7 pages, 2 figures - Proceeding of the 34th International Cosmic Ray
Conferenc
Cosmic-ray protons, nuclei, electrons, and antiparticles under a two-halo scenario of diffusive propagation
We report calculations of cosmic-ray proton, nuclei, antiproton, electron and
positron energy spectra within a "two-halo model" of diffusive transport. The
two halos represent a simple, physically consistent generalization of the
standard diffusion models, which assume a unique type of diffusion for cosmic
rays in the whole Galactic halo. We believe instead that cosmic rays may
experience a smaller energy dependence of diffusion when they are in proximity
of the Galactic disk. Our scenario is supported by recent observations of
cosmic-ray protons, nuclei, anisotropy, and gamma-rays. We predict remarkably
hard antiparticle spectra at high energy. In particular, at E>10 GeV, the
antiproton/proton ratio is expected to flatten, while the positron fraction is
found to increase with energy. We discuss the implications for cosmic-ray
physics and dark matter searches via antimatter.Comment: 5 pages, 4 figures, matches version published in PRD - Rapid
Communicatio
Examination of uncertainties in nuclear data for cosmic ray physics with the AMS experiment
High-energy Li-Be-B nuclei in cosmic rays are being measured with unprecedent
accuracy by the AMS experiment. These data bring valuable information to the
cosmic ray propagation physics. In particular, combined measurements of B/C and
Be/B ratios may allow to break the parameter degeneracy between the cosmic-ray
diffusion coefficient and the size of the propagation region, which is crucial
for dark matter searches. The parameter determination relies in the calculation
of the Be and B production from collisions of heavier nuclei with the gas.
Using the available cross-section data, I present for the first time an
evaluation of the nuclear uncertainties and their impact in constraining the
propagation models. I found that the AMS experiment can provide tight
constraints on the transport parameters allowing to resolutely break the
degeneracy, while nuclear uncertainties in the models are found to be a major
limiting factor. Once these uncertainties are accounted, the degeneracy remains
poorly resolved. In particular, the Be/B ratio at ~1 - 10 GeV/n is found not to
bring valuable information for the parameter extraction. On the other hand,
precise Be/B data at higher energy may be useful to test the nuclear physics
inputs of the models.Comment: 4 figures, 6 pages, matches published versio
Solar Modulation of Galactic Cosmic Rays: Physics Challenges for AMS-02
The Alpha Magnetic Spectrometer (AMS) is a new generation high-energy physics
experiment installed on the International Space Station in May 2011 and
operating continuously since then. Using an unprecedently large collection of
particles and antiparticles detected in space, AMS is performing precision
measurements of cosmic ray energy spectra and composition. In this paper, we
discuss the physics of solar modulation in Galactic cosmic rays that can be
investigated with AMS my means of dedicated measurements on the time-dependence
of cosmic-ray proton, helium, electron and positron fluxes.Comment: Proceedings of the 18th Lomonosov Conference - 2017, Moscow, Russi
Origin of the Proton-to-Helium Ratio Anomaly in Cosmic Rays
Recent data on Galactic cosmic rays (CRs) revealed that the helium energy
spectrum is harder than the proton spectrum. The AMS experiment has now
reported that the proton-to-helium ratio as function of rigidity
(momentum-to-charge ratio) falls off steadily as p/He , with
-0.08 between 40 GV and 2 TV. Besides, the single
spectra of proton and helium are found to progressively harden at 100
GV. The p/He anomaly is generally ascribed to particle-dependent acceleration
mechanisms occurring in Galactic CR sources. However, this explanation poses a
challenge to the known mechanisms of particle acceleration since they are
believed to be "universal", composition blind, rigidity mechanisms. Using the
new AMS data, we show that the p/He anomaly can be simply explained in terms of
a two-component scenario where the GeV-TeV flux is ascribed to a hydrogen-rich
source, possibly a nearby supernova remnant, characterized by a soft
acceleration spectrum. This simple idea provides a common interpretation for
the p/He ratio and for the single spectra of proton and helium: both anomalies
are explained by a flux transition between two components. The "universality"
of particle acceleration in sources is not violated in this model. A
distinctive signature of our scenario is the high-energy flattening of the p/He
ratio at multi-TeV energies, which is hinted at by existing data and will be
resolutely tested by new space experiments ISS-CREAM and CALET.Comment: 5 pages, 4 figures; matches the published versio
Consistent description of leptonic and hadroninc spectra in cosmic rays
The AMS Collaboration has recently released data on cosmic ray (CR) leptons
and hadrons that can shed light on two exciting problems in CR physics: on one
side, the origin of the rise of the CR positron fraction above ~10 GeV of
energy, on the other side, the nature of the spectral features observed in CR
protons and helium at TeV energies. Concerning heavier nuclei, The ATIC-2
experiment has recently reported an puzzling spectral upturn at energy ~50 GeV
per nucleon in several primary/primary ratios involving Iron, such as the O/Fe
or C/Fe ratio. In this work, the AMS data are described using a two-component
scenario, where the total CR flux is provided by a mixture of fluxes
accelerated by sources with different properties. Within this picture, the role
of secondary CR production inside nearby supernova remnants is discussed. In
particular, we present the predictions of our model for the C/Fe and O/Fe
ratios, in connection with the spectral anomalies found by the ATIC-2
experiment.Comment: 8 pages, 2 figures - Proceeding of the 34th International Cosmic Ray
Conference. PoS(2015) 55
Production of cosmic-ray antinuclei in the Galaxy and background for dark matter searches
Antimatter nuclei in cosmic rays (CR) represent a promising discovery channel
for the indirect search of dark matter. We present astrophysical background
calculations of CR antideuteron () and antihelium
(). These particles are produced by high-energy collisions of CR
protons and nuclei with the gas nuclei of the interstellar medium. In our
calculations, we also consider production and shock acceleration of antinuclei
in the shells of supernova remnants (SNRs). The total flux of
and particles is constrained using new AMS measurements on the
boron/carbon (B/C) and antiproton/proton () ratios. The two ratios
leads to different antiparticle fluxes in the high-energy regime 10
GeV/n where, in particular, -driven calculations leads to a
significantly larger antiparticle flux in comparison to predictions from
conventional B/C-driven constraints. On the other hand, both approaches provide
consistent results in the sub-GeV/n energy window, which is where dark matter
induced signal may exceed the astrophysical background. In this region, the
total antinuclei flux, from interaction in the insterstellar gas and inside
SNRs, is tightly bounded by the data. Shock-acceleration of antiparticles in
SNRs has a minor influence in the astrophysical background for dark matter
searches.Comment: Proceedings of the EPS Conference on High Energy Physics EPS-HEP
2017, Venic
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