scholarly journals Implications of a possible TeV break in the cosmic-ray electron and positron flux

2021 ◽  
Vol 103 (11) ◽  
Author(s):  
Yu-Chen Ding ◽  
Nan Li ◽  
Chun-Cheng Wei ◽  
Yue-Liang Wu ◽  
Yu-Feng Zhou
Keyword(s):  
Cosmic Ray ◽  
Positron Flux

scholarly journals Properties of Elementary Particle Fluxes in Primary Cosmic Rays Measured with the Alpha Magnetic Spectrometer on the International Space Station

2019 ◽  
Vol 209 ◽  
pp. 01007
Author(s):  
Francesco Nozzoli
Keyword(s):  
Electron Flux ◽  
Space Station ◽  
Cosmic Ray ◽  
High Energy ◽  
Precision Measurements ◽  
High Energy Electrons ◽  
Electrons And Positrons ◽  
Positron Flux ◽  
Rigidity Dependence ◽  
Alpha Magnetic Spectrometer

Precision measurements by AMS of the fluxes of cosmic ray positrons, electrons, antiprotons, protons as well as their rations reveal several unexpected and intriguing features. The presented measurements extend the energy range of the previous observations with much increased precision. The new results show that the behavior of positron flux at around 300 GeV is consistent with a new source that produce equal amount of high energy electrons and positrons. In addition, in the absolute rigidity range 60–500 GV, the antiproton, proton, and positron fluxes are found to have nearly identical rigidity dependence and the electron flux exhibits different rigidity dependence.

scholarly journals The pinching method for Galactic cosmic ray positrons: Implications in the light of precision measurements

2017 ◽  
Vol 605 ◽  
pp. A17 ◽  
Author(s):  
M. Boudaud ◽  
E. F. Bueno ◽  
S. Caroff ◽  
Y. Genolini ◽  
V. Poulin ◽  
...  
Keyword(s):  
Dark Matter ◽  
Cosmic Ray ◽  
High Energy ◽  
Transport Processes ◽  
Secondary Component ◽  
Dark Matter Annihilation ◽  
Propagation Parameters ◽  
Positron Flux ◽  
Galactic Cosmic Ray ◽  
Best Fit

Context. Two years ago, the Ams-02 collaboration released the most precise measurement of the cosmic ray positron flux. In the conventional approach, in which positrons are considered as purely secondary particles, the theoretical predictions fall way below the data above 10 GeV. One suggested explanation for this anomaly is the annihilation of dark matter particles, the so-called weakly interactive massive particles (WIMPs), into standard model particles. Most analyses have focused on the high-energy part of the positron spectrum, where the anomaly lies, disregarding the complicated GeV low-energy region where Galactic cosmic ray transport is more difficult to model and solar modulation comes into play. Aims. Given the high quality of the latest measurements by Ams-02, it is now possible to systematically re-examine the positron anomaly over the entire energy range, this time taking into account transport processes so far neglected, such as Galactic convection or diffusive re-acceleration. These might impact somewhat on the high-energy positron flux so that a complete and systematic estimate of the secondary component must be performed and compared to the Ams-02 measurements. The flux yielded by WIMPs also needs to be re-calculated more accurately to explore how dark matter might source the positron excess. Methods. We devise a new semi-analytical method to take into account transport processes thus far neglected, but important below a few GeV. It is essentially based on the pinching of inverse Compton and synchrotron energy losses from the magnetic halo, where they take place, inside the Galactic disc. The corresponding energy loss rate is artificially enhanced by the so-called pinching factor, which needs to be calculated at each energy. We have checked that this approach reproduces the results of the Green function method at the per mille level. This new tool is fast and allows one to carry out extensive scans over the cosmic ray propagation parameters. Results. We derive the positron flux from sub-GeV to TeV energies for both gas spallation and dark matter annihilation. We carry out a scan over the cosmic ray propagation parameters, which we strongly constrain by requiring that the secondary component does not overshoot the Ams-02 measurements. We find that only models with large diffusion coefficients are selected by this test. We then add to the secondary component the positron flux yielded by dark matter annihilation. We carry out a scan over WIMP mass to fit the annihilation cross-section and branching ratios, successively exploring the cases of a typical beyond-the-standard-model WIMP and an annihilation through light mediators. In the former case, the best fit yields a p-value of 0.4% for a WIMP mass of 264 GeV, a value that does not allow to reproduce the highest energy data points. If we require the mass to be larger than 500 GeV, the best-fit χ2 per degree of freedom always exceeds a value of 3. The case of light mediators is even worse, with a best-fit χ2 per degree of freedom always larger than 15. Conclusions. We explicitly show that the cosmic ray positron flux is a powerful and independent probe of Galactic cosmic ray propagation. It should be used as a complementary observable to other tracers such as the boron-to-carbon ratio. This analysis shows also that the pure dark matter interpretation of the positron excess is strongly disfavoured. This conclusion is based solely on the positron data, and no other observation, such as the antiproton flux or the CMB anisotropies, needs to be invoked.

NEW MEASUREMENTS OF COSMIC RAY POSITRONS

1995 ◽  
Vol 10 (36) ◽  
pp. 2727-2732
Author(s):  
K.K. TANG
Keyword(s):  
Interstellar Medium ◽  
Secondary Production ◽  
Cosmic Ray ◽  
Simple Interpretation ◽  
Positron Fraction ◽  
Decay Products ◽  
Positron Flux ◽  
Balloon Experiments ◽  
Simple Picture ◽  
Existing Data

Cosmic ray electrons consists of mostly negative electrons and a relatively smaller flux of positrons. A simple interpretation is that all the positrons, together with an approximately equal flux of negative electrons, are decay products of pions created in the interaction of cosmic ray protons with the interstellar medium, and the remaining negative electrons are produced in primary cosmic ray sources. However, the existing data on the positron fraction (e+/e++e−) does not support this simple picture. While the positron flux around a few GeV can be explained by the secondary production, there are apparently excesses of positrons both at lower and higher energies. This has stimulated many interpretation and conjectures of new astrophysical sources of positrons. Recently, there are new measurements from four different balloon experiments. They begin to show some discrepancy with the old data. A brief summary of the new results and their impact is given here.

scholarly journals Cosmic-ray positrons strongly constrain leptophilic dark matter

2021 ◽  
Vol 2021 (12) ◽  
pp. 007
Author(s):  
Isabelle John ◽  
Tim Linden
Keyword(s):  
Dark Matter ◽  
Cross Section ◽  
Cosmic Ray ◽  
Propagation Model ◽  
Annihilation Cross Section ◽  
Secondary Component ◽  
Spectral Features ◽  
Dark Matter Annihilation ◽  
Positron Fraction ◽  
Positron Flux

Abstract Cosmic-ray positrons have long been considered a powerful probe of dark matter annihilation. In particular, myriad studies of the unexpected rise in the positron fraction have debated its dark matter or pulsar origins. In this paper, we instead examine the potential for extremely precise positron measurements by AMS-02 to probe hard leptophilic dark matter candidates that do not have spectral features similar to the bulk of the observed positron excess. Utilizing a detailed cosmic-ray propagation model that includes a primary positron flux generated by Galactic pulsars in addition to a secondary component constrained by He and proton measurements, we produce a robust fit to the local positron flux and spectrum. We find no evidence for a spectral bump correlated with leptophilic dark matter, and set strong constraints on the dark matter annihilation cross-section that fall below the thermal annihilation cross-section for dark matter masses below 60 GeV and 380 GeV for annihilation into τ+τ- and e+e-, respectively, in our default model.

Electron component in primary cosmic rays. II. Theory

1968 ◽  
Vol 46 (10) ◽  
pp. S533-S535
Author(s):  
A. Danjo ◽  
S. Hayakawa ◽  
F. Makino ◽  
H. Obayashi
Keyword(s):  
Cosmic Rays ◽  
Scattering Length ◽  
Cosmic Ray ◽  
Critical Energy ◽  
Galactic Cosmic Rays ◽  
Particle Diffusion ◽  
Electron Component ◽  
Positron Flux ◽  
Energy Formula ◽  
The Mean

The energy spectrum of cosmic-ray electrons can be represented by a power law with a single exponent between 3 and 50 GeV, and a break in the spectrum due to the energy loss of electrons could appear at about 50 GeV or higher. It is necessary to reconcile this high value of the critical energy [Formula: see text] with the effective thickness of matter traversed [Formula: see text] as estimated from the positron flux) and with the small amplitude of anisotropy [Formula: see text]. Hence rather severe conditions are imposed on the properties of the region in which cosmic rays are stored. We have carried out an investigation of the two-component model for storing galactic cosmic rays, which consists of disk and halo components. Assuming the intensity ratio (η) of the halo to the disk components to be nearly unity, one can assign parameters explaining various properties of cosmic rays consistently. For the case of a vanishing halo component (η = 0), the mean scattering length for particle diffusion becomes about 1018 cm.

scholarly journals Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth

Science ◽  
2017 ◽  
Vol 358 (6365) ◽  
pp. 911-914 ◽  
Author(s):  
A. U. Abeysekara ◽  
A. Albert ◽  
R. Alfaro ◽  
C. Alvarez ◽  
J. D. Álvarez ◽  
...  
Keyword(s):  
Dark Matter ◽  
High Altitude ◽  
Secondary Production ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Flux ◽  
Emission Profile ◽  
Electron Volt ◽  
Local Sources ◽  
Positron Flux

The unexpectedly high flux of cosmic-ray positrons detected at Earth may originate from nearby astrophysical sources, dark matter, or unknown processes of cosmic-ray secondary production. We report the detection, using the High-Altitude Water Cherenkov Observatory (HAWC), of extended tera–electron volt gamma-ray emission coincident with the locations of two nearby middle-aged pulsars (Geminga and PSR B0656+14). The HAWC observations demonstrate that these pulsars are indeed local sources of accelerated leptons, but the measured tera–electron volt emission profile constrains the diffusion of particles away from these sources to be much slower than previously assumed. We demonstrate that the leptons emitted by these objects are therefore unlikely to be the origin of the excess positrons, which may have a more exotic origin.

scholarly journals Dissecting cosmic-ray electron-positron data with Occam’s razor: the role of known pulsars

Open Physics ◽  
2012 ◽  
Vol 10 (1) ◽  
pp. 1-31 ◽  
Author(s):  
Stefano Profumo
Keyword(s):  
Gamma Ray ◽  
Decisive Role ◽  
Cosmic Ray ◽  
High Energy ◽  
Current Data ◽  
Energy Output ◽  
Total Electron ◽  
Positron Fraction ◽  
Electron Positron ◽  
Positron Flux

AbstractWe argue that both the positron fraction measured by PAMELA and the peculiar spectral features reported in the total electron-positron flux measured by ATIC have a very natural explanation in electron-positron pairs produced by nearby pulsars. While this possibility was pointed out a long time ago, the greatly improved quality of current data potentially allow to reverse-engineer the problem: given the regions of pulsar parameter space favored by PAMELA and by ATIC, are there known pulsars that explain the data with reasonable assumptions on the injected electron-positron pairs? In the context of simple benchmark models for estimating the electron-positron output, we consider all known pulsars, as listed in the most complete available catalogue. We find that it is unlikely that a single pulsar be responsible for both the PAMELA positron fraction anomaly and for the ATIC excess, although two single sources are in principle enough to explain both experimental results. The PAMELA excess positrons likely come from a set of mature pulsars (age ∼ × 106 yr), with a distance of 0.8–1 kpc, or from a single, younger and closer source like Geminga. The ATIC data require a larger (and less plausible) energy output, and favor an origin associated to powerful, more distant (1–2 kpc) and younger (age ∼ × 5 × 105 yr) pulsars. We list several candidate pulsars that can individually or coherently contribute to explain the PAMELA and ATIC data. Although generally suppressed, we find that the contribution of pulsars more distant than 1–2 kpc could contribute for the ATIC excess. Finally, we stress the multi-faceted and decisive role that Fermi-LAT will play in the very near future by (1) providing us with an exquisite measurement of the electron-positron flux, (2) unveiling the existence of as yet undetected gamma-ray pulsars, and (3) searching for anisotropies in the arrival direction of high-energy electrons and positrons.

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