Fluxes Of Cosmic Ray Nuclei Research Articles

Fresh insights on properties of particle fluxes in cosmic rays measured with the Alpha Magnetic Spectrometer on the international space station

The Alpha Magnetic Spectrometer is a particle physics detector focusing on the search for dark matter, the existence of antimatter, the origin and composition of cosmic rays from primordial sources in the universe and the exploration of new physics in space. Important features of the elementary particle (proton, antiproton, positron and election) fluxes in cosmic rays are presented: (1) The proton spectrum has a smooth hardening from 200 GeV; (2) antiproton and positron spectra show excess from traditional physics background; (3) in particular, the positron flux shows a source term with a cutoff energy of 810 GeV, which raises the question of its source; (4) the origin of the energetic electrons is different from that of positrons and (5) the identical momentum dependence of primary and secondary cosmic ray nuclei fluxes are also reviewed.

Measurements of nuclear interaction cross sections with the Alpha Magnetic Spectrometer on the International Space Station

Precise knowledge of nuclear interactions with the detector materials is crucial for the accurate measurements of cosmic-ray nuclei fluxes. We have measured the interaction cross sections on carbon target for various nuclear species with charge 2≤Z≤16 in a wide rigidity (momentum/charge) range from a few GV to TV, using cosmic-ray nuclei events collected by the Alpha Magnetic Spectrometer. The properties of the measured nuclear interaction cross sections are discussed.

Breaks in interstellar spectra of positrons and electrons derived from time-dependent AMS data

Until fairly recently, it was widely accepted that local cosmic ray spectra were largely featureless power laws, containing limited information on their acceleration and transport. This viewpoint is currently being revised in the light of evidence for a variety of spectral breaks in the fluxes of cosmic ray nuclei. Here, we focus on cosmic ray electrons and positrons which at the highest energies must be of local origin due to strong radiative losses. We consider a pure diffusion model for their Galactic transport and determine its free parameters by fitting data in a wide energy range: measurements of the interstellar spectrum by Voyager at MeV energies, radio synchrotron data (sensitive to GeV electrons and positrons) and local observations by AMS up to ~ 1 TeV. For the first time, we also model the time-dependent fluxes of cosmic ray electrons and positrons at GeV energies recently presented by AMS, treating solar modulation in a simple extension of the widely used force-field approximation. We are able to reproduce all the available measurements to date. Our model of the interstellar spectrum of cosmic ray electrons and positrons requires the presence of a number of spectral breaks, both in the source spectra and the diffusion coefficients. While we remain agnostic as to the origin of these spectral breaks, their presence will inform future models of the microphysics of cosmic ray acceleration and transport.

A System for Generating the Trigger Signals of the Spaceborne GAMMA-400 Telescope

The GAMMA-400 space project is one of the new generation of space observatories designed to search for signs of dark matter in the cosmic gamma emission, and to measure the characteristics of diffuse gamma-ray emission and gamma-rays from the Sun during periods of solar activity; gamma-ray bursts; extended and point gamma-ray sources; and electron, positron, and cosmic-ray nuclei fluxes with energies in the TeV ranges. The GAMMA-400 γ-ray telescope constitutes the core of the scientific instrumentation. The nature of the intended experiments imposes stringent requirements on the gamma telescope’s system of trigger signal formation, now being developed using the state-of-the-art logic devices and fast data links. The design concept of the system is discussed, along with the chosen engineering solutions and some experimental results obtained during the operation of the system prototype using a positron beam with energies of 100–300 MeV from the PAKHRA S-25R synchrotron at the Lebedev Physical Institute.

The structure, logic of operation and distinctive features of the system of triggers and counting signals formation for gamma-telescope GAMMA-400

Scientific project GAMMA-400 (Gamma Astronomical Multifunctional Modular Apparatus) relates to the new generation of space observatories intended to perform an indirect search for signatures of dark matter in the cosmic-ray fluxes, measurements of characteristics of diffuse gamma-ray emission and gamma-rays from the Sun during periods of solar activity, gamma-ray bursts, extended and point gamma-ray sources, electron/positron and cosmic-ray nuclei fluxes up to TeV energy region by means of the GAMMA-400 gamma-ray telescope represents the core of the scientific complex. The system of triggers and counting signals formation of the GAMMA-400 gamma-ray telescope constitutes the pipelined processor structure which collects data from the gamma-ray telescope subsystems and produces summary information used in forming the trigger decision for each event. The system design is based on the use of state-of-the-art reconfigurable logic devices and fast data links. The basic structure, logic of operation and distinctive features of the system are presented.

The Prototype of GAMMA-400 Apparatus

Scientific project GAMMA-400 (Gamma-Astronomy Multifunction Modules Apparatus) relates to the new generation of space observatories for investigation of cosmic γ-emission in the energy band from ∼20 MeV up to several TeV, electron/positron fluxes from ∼1GeV up to ∼10 TeV and cosmic-ray nuclei fluxes with energies up to ∼1015 eV by means of GAMMA-400 gamma-telescope represents the core of the scientific complex. The investigation of gamma ray bursts in the energy band of 10 keV–15 MeV are possible too by means of KONUS-FG apparatus included in the complex. For γ-rays in the energy region from 10 to 100GeV expected energy resolution changes from ∼3% to ∼1% and angular resolution from ∼0.1% to ∼ 0.01% respectively, γ/protons rejection factor is ∼5·105. The GAMMA-400 satellite will be launched at the beginning of the next decade on the high apogee orbit with following initial parameters: apogee altitude ∼300000km, perigee altitude ∼500km, rotation period ∼7 days, inclination to the equator plane 51.4°. The active functioning interval will be 7-10 years. The scientific complex will have next main technical parameters: total weight ∼4100kg, power consumption ∼2000W, information quote 100 GByte/day. During the project development, the prototype of apparatus was created for working-off of the main apparatus construction units in laboratory conditions. The main distinctive features of the prototype are presented.

The Application of Sensl Silicon Photomultipliers in GAMMA–400 Satellite Project

Scientific project GAMMA-400 (Gamma-Astronomy Multifunction Modules Apparatus) relates to the new generation of space observatories for investigation of cosmic γ-emission in the energy band from ∼20 MeV up to several TeV, electron/positron fluxes from ∼1 GeV up to ∼10 TeV and cosmic-ray nuclei fluxes with energies up to ∼1015 eV. The core of the scientific complex is gamma-telescope GAMMA-400. It contains a set of detecting systems using so-called “segmentation” principle and consists of a large amount of scintillation elements (∼1200 by current apparatus design). The utilization of vacuum PMT as the light sensors for scintillation elements arouses a number of serious problems connected with the apparatus weight and dimensions restrictions, power consumption, reliability requirements and so on. An alternative solution – the application of silicon photomultipliers as the light sensors for scintillation detectors is considered.

New results on source and diffusion spectral features of Galactic cosmic rays: I $\vec{B/C}$ ratio

In a previous study (Maurin et al., 2001), we explored the set of parameters describing diffusive propagation of cosmic rays (galactic convection, reacceleration, halo thickness, spectral index and normalization of the diffusion coefficient), and we identified those giving a good fit to the measured B/C ratio. This study is now extended to take into account a sixth free parameter, namely the spectral index of sources. We use an updated version of our code where the reacceleration term comes from standard minimal reacceleration models. The goal of this paper is to present a general view of the evolution of the goodness of fit to B/C data with the propagation parameters. In particular, we find that, unlike the well accepted picture, and in accordance with our previous study, a Kolmogorov-like power spectrum for diffusion is strongly disfavored. Rather, the $\chi^2$ analysis points towards $\delta\gtrsim 0.7$ along with source spectra index $\lesssim 2.0$. Two distinct energy dependences are used for the source spectra: the usual power-law in rigidity and a law modified at low energy, the second choice being only slightly preferred. We also show that the results are not much affected by a different choice for the diffusion scheme. Finally, we compare our findings to recent works, using other propagation models. This study will be further refined in a companion paper, focusing on the fluxes of cosmic ray nuclei.

Cosmic Rays belowZ = 30 in a Diffusion Model: New Constraints on Propagation Parameters

Cosmic ray nuclei fluxes are expected to be measured with high precision in the near future. For instance, high quality data on the antiproton component could give important clues about the nature of the astronomical dark matter. A very good understanding of the different aspects of cosmic ray propagation is therefore necessary. In this paper, we use cosmic ray nuclei data to give constraints on the diffusion parameters. Propagation is studied with semi-analytical solutions of a diffusion model, and we give new analytical solutions for radioactively produced species. Our model includes convection and reacceleration as well as the standard energy losses. We perform a $\chi^2$ analysis over B/C data for a large number of configurations obtained by varying the relevant parameters of the diffusion model. A very good agreement with B/C data arises for a number of configurations, all of which are compatible with sub-Fe/Fe data. Different source spectra $Q(E)$ and diffusion coefficients $K(E)$ have been tried, but for both parameters only one form gives a good fit. Another important result is that models without convection or without reacceleration are excluded. We find that the various parameters, i.e. the diffusion coefficient normalisation $K_0$ and spectral index $\delta$, the halo thickness $L$, the Alfv\'en velocity $V_a$, and the convection velocity $V_c$ are strongly correlated. We obtain limits on the spectral index $\delta$ of thediffusion coefficient, and in particular we exclude a Kolmogorov spectrum ($\delta = 1/3$).

Do energetic heavy nuclei penetrate deeply into Earth's atmosphere?

We calculate the expected fluxes of cosmic ray nuclei with charge 5 </= Z </= 28 at various depths in the earth's atmosphere, taking into account the initial charge distribution, ionization loss, and various modes of fragmentation. The flux of surviving heavy nuclei is too low by a factor approximately 10(-10) to account for the ultra-high-energy Centauro events. We describe an experiment to search for highly ionizing particles that may or may not be nuclei.