New Measurement of the Cosmic-Ray Positron Fraction from 5 to 15 GeV

Beatty, J. J.; Bhattacharyya, Amit; Bower, C.; Coutu, S.; DuVernois, Michael; Kee, S. P. Mc; Minnick, S.; Müller, D.; Musser, J.; Nutter, S.; Labrador, A. W.; Schubnell, M.; Swordy, S. P.; Tarlè, G.; Tomasch, A.

doi:10.1103/physrevlett.93.241102

Cited by 204 publications

(114 citation statements)

References 28 publications

(39 reference statements)

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“…In the bottom right panel of Fig. 14, we have used the data from HEAT (Barwick et al 1997;Beatty et al 2004), AMS-01 (AMS-01 Collaboration et al 2007), and PAMELA (PAMELA Collaboration et al 2010). From this plot, our template calculation turns out to be consistent with the data, especially above 10 GeV.…”

Section: Positron Fractionmentioning

confidence: 99%

Galactic electrons and positrons at the Earth: new estimate of the primary and secondary fluxes

Delahaye

Lavalle

Lineros

et al. 2010

A&A

201

334

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Context. The so-called excess of cosmic ray (CR) positrons observed by the PAMELA satellite up to 100 GeV has led to many interpretation attempts, from standard astrophysics to a possible exotic contribution from dark matter annihilation or decay. The Fermi data subsequently obtained about CR electrons and positrons in the range 0.02-1 TeV, and HESS data above 1 TeV have provided additional information about the leptonic content of local Galactic CRs. Aims. We analyse predictions of the CR lepton fluxes at the Earth of both secondary and primary origins, evaluate the theoretical uncertainties, and determine their level of consistency with respect to the available data. Methods. For propagation, we use a relativistic treatment of the energy losses for which we provide useful parameterizations. We compute the secondary components by improving on the method that we derived earlier for positrons. For primaries, we estimate the contributions from astrophysical sources (supernova remnants and pulsars) by considering all known local objects within 2 kpc and a smooth distribution beyond. Results. We find that the electron flux in the energy range 5-30 GeV is well reproduced by a smooth distant distribution of sources with index γ ∼ 2.3−2.4, while local sources dominate the flux at higher energy. For positrons, local pulsars have an important effect above 5-10 GeV. Uncertainties affecting the source modeling and propagation are degenerate and each translates into about one order of magnitude error in terms of local flux. The spectral shape at high energy is weakly correlated with the spectral indices of local sources, but more strongly with the hierarchy in their distance, age and power. Despite the large theoretical errors that we describe, our global and self-consistent analysis can explain all available data without over-tuning the parameters, and therefore without the need to consider any exotic physics. Conclusions. Though a standard paradigm of Galactic CRs is well established, our results show that we can hardly talk about any standard model of CR leptons, because of the very large theoretical uncertainties. Our analysis provides details about the impact of these uncertainties, thereby sketching a roadmap for future improvements.

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Section: Positron Fractionmentioning

confidence: 99%

Galactic electrons and positrons at the Earth: new estimate of the primary and secondary fluxes

Delahaye

Lavalle

Lineros

et al. 2010

A&A

201

334

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“…Observations by the HighEnergy Antimatter Telescope (HEAT) collaboration (Barwick et al 1997;DuVernois et al 2001;Beatty et al 2004) already hinted at a slight deviation of the flux with respect to a pure secondary component. The anomaly was clearly established…”

Section: Introductionmentioning

confidence: 99%

A new look at the cosmic ray positron fraction

Boudaud

Aupetit

Caroff

et al. 2015

A&A

130

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Context. The positron fraction in cosmic rays has recently been measured with improved accuracy up to 500 GeV, and it was found to be a steadily increasing function of energy above ∼10 GeV. This behaviour contrasts with standard astrophysical mechanisms, in which positrons are secondary particles, produced in the interactions of primary cosmic rays during their propagation in the interstellar medium. The observed anomaly in the positron fraction triggered a lot of excitement, as it could be interpreted as an indirect signature of the presence of dark matter species in the Galaxy, the so-called weakly interacting massive particles (WIMPs). Alternatively, it could be produced by nearby sources, such as pulsars. Aims. These hypotheses are probed in light of the latest AMS-02 positron fraction measurements. As regards dark matter candidates, regions in the annihilation cross section to mass plane, which best fit the most recent data, are delineated and compared to previous measurements. The explanation of the anomaly in terms of a single nearby pulsar is also explored. Methods. The cosmic ray positron transport in the Galaxy is described using a semi-analytic two-zone model. Propagation is described with Green functions as well as with Bessel expansions. For consistency, the secondary and primary components of the positron flux are calculated together with the same propagation model. The above mentioned explanations of the positron anomaly are tested using χ 2 fits. The numerical package MicrOMEGAs is used to model the positron flux generated by dark matter species. The description of the positron fraction from conventional astrophysical sources is based on the pulsar observations included in the Australia Telescope National Facility (ATNF) catalogue. Results. The masses of the favoured dark matter candidates are always larger than 500 GeV, even though the results are very sensitive to the lepton flux. The Fermi measurements point systematically to much heavier candidates than the recently released AMS-02 observations. Since the latter are more precise, they are much more constraining. A scan through the various individual annihilation channels disfavours leptons as the final state. On the contrary, the agreement is excellent for quark, gauge boson, or Higgs boson pairs, with best-fit masses in the 10 to 40 TeV range. The combination of annihilation channels that best matches the positron fraction is then determined at fixed WIMP mass. A mixture of electron and tau lepton pairs is only acceptable around 500 GeV. Adding b-quark pairs significantly improves the fit up to a mass of 40 TeV. Alternatively, a combination of the four-lepton channels provides a good fit between 0.5 and 1 TeV, with no muons in the final state. Concerning the pulsar hypothesis, the region of the distance-to-age plane that best fits the positron fraction for a single source is determined. Conclusions. The only dark matter species that fulfils the stringent gamma ray and cosmic microwave background bounds is a particle annihilating into...

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“…The HEAT experiment (Barwick et al 1997;Beatty et al 2004) showed that the positron fraction (the ratio of the positron to the total electron-positron fluxes) possibly exhibits an unexpected bump in the 10 GeV region of the spectrum. Although this bump could be due to some unknown systematic effect, the HEAT result has triggered many explanations.…”

Section: Introductionmentioning

confidence: 99%

Galactic secondary positron flux at the Earth

Delahaye

Lineros²,

Donato³

et al. 2009

A&A

217

308

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Context. Secondary positrons are produced by spallation of cosmic rays within the interstellar gas. Measurements have been typically expressed in terms of the positron fraction, which exhibits an increase above 10 GeV. Many scenarios have been proposed to explain this feature, among them some additional primary positrons originating from dark matter annihilation in the Galaxy. Aims. The PAMELA satellite has provided high quality data that has enabled high accuracy statistical analyses to be made, showing that the increase in the positron fraction extends up to about 100 GeV. It is therefore of paramount importance to constrain theoretically the expected secondary positron flux to interpret the observations in an accurate way. Methods. We focus on calculating the secondary positron flux by using and comparing different up-to-date nuclear cross-sections and by considering an independent model of cosmic ray propagation. We carefully study the origins of the theoretical uncertainties in the positron flux. Results. We find the secondary positron flux to be reproduced well by the available observations, and to have theoretical uncertainties that we quantify to be as large as about one order of magnitude. We also discuss the positron fraction issue and find that our predictions may be consistent with the data taken before PAMELA. For PAMELA data, we find that an excess is probably present after considering uncertainties in the positron flux, although its amplitude depends strongly on the assumptions made in relation to the electron flux. By fitting the current electron data, we show that when considering a soft electron spectrum, the amplitude of the excess might be far lower than usually claimed. Conclusions. We provide fresh insights that may help to explain the positron data with or without new physical model ingredients. PAMELA observations and the forthcoming AMS-02 mission will allow stronger constraints to be aplaced on the cosmic-ray transport parameters, and are likely to reduce drastically the theoretical uncertainties.

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New Measurement of the Cosmic-Ray Positron Fraction from 5 to 15 GeV

Cited by 204 publications

References 28 publications

Galactic electrons and positrons at the Earth: new estimate of the primary and secondary fluxes

Galactic electrons and positrons at the Earth: new estimate of the primary and secondary fluxes

A new look at the cosmic ray positron fraction

Galactic secondary positron flux at the Earth

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