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Nature
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An anomalous positron abundance in cosmic rays with energies 1.5–100 GeV

Naturevolume 458, pages607–609 (2009)Cite this article

Abstract

Antiparticles account for a small fraction of cosmic rays and are known to be produced in interactions between cosmic-ray nuclei and atoms in the interstellar medium1, which is referred to as a ‘secondary source’. Positrons might also originate in objects such as pulsars2 and microquasars3 or through dark matter annihilation4, which would be ‘primary sources’. Previous statistically limited measurements5,6,7 of the ratio of positron and electron fluxes have been interpreted as evidence for a primary source for the positrons, as has an increase in the total electron+positron flux at energies between 300 and 600 GeV (ref.8). Here we report a measurement of the positron fraction in the energy range 1.5–100 GeV. We find that the positron fraction increases sharply over much of that range, in a way that appears to be completely inconsistent with secondary sources. We therefore conclude that a primary source, be it an astrophysical object or dark matter annihilation, is necessary.

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Figure 1:Calorimeter energy fraction, .
Figure 2:PAMELA positron fraction with other experimental data and with secondary production model.

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Acknowledgements

We thank D. Marinucci for discussions concerning statistical methods, D. Müller, S. Swordy and their group at University of Chicago, G. Bellettini and G. Chiarelli for discussions about the data analysis and L. Bergström for comments on the interpretation of our results. We acknowledge support from The Italian Space Agency (ASI), Deutsches Zentrum für Luftund Raumfahrt (DLR), The Swedish National Space Board, The Swedish Research Council, The Russian Space Agency (Roscosmos) and The Russian Foundation for Basic Research.

Author information

Authors and Affiliations

  1. Department of Physics, University of Florence, Via Sansone 1, I-50019 Sesto Fiorentino, Florence, Italy,

    O. Adriani, L. Bonechi & P. Spillantini

  2. INFN, Sezione di Florence, Via Sansone 1, I-50019 Sesto Fiorentino, Florence, Italy ,

    O. Adriani, L. Bonechi, M. Bongi, S. Bottai, P. Papini, S. B. Ricciarini, P. Spillantini & E. Vannuccini

  3. Department of Physics, University of Naples “Federico II”, Via Cintia, I-80126 Naples, Italy,

    G. C. Barbarino

  4. INFN, Sezione di Naples, Via Cintia, I-80126 Naples, Italy ,

    G. C. Barbarino, D. Campana, G. De Rosa & G. Osteria

  5. Lebedev Physical Institute, Leninsky Prospekt 53, RU-119991 Moscow, Russia ,

    G. A. Bazilevskaya, A. N. Kvashnin & Y. I. Stozhkov

  6. Department of Physics, University of Bari, Via Amendola 173, I-70126 Bari, Italy,

    R. Bellotti & A. Bruno

  7. INFN, Sezione di Bari, Via Amendola 173, I-70126 Bari, Italy ,

    R. Bellotti, A. Bruno & F. Cafagna

  8. INFN, Sezione di Trieste, Padriciano 99, I-34012 Trieste, Italy ,

    M. Boezio, V. Bonvicini, E. Mocchiutti, A. Vacchi, G. Zampa & N. Zampa

  9. Ioffe Physical Technical Institute, Polytekhnicheskaya 26, RU-194021 St Petersburg, Russia ,

    E. A. Bogomolov, S. Y. Krutkov & G. Vasilyev

  10. Department of Physics, KTH, AlbaNova University Centre, SE-10691 Stockholm, Sweden

    P. Carlson, P. Hofverberg & S. Orsi

  11. INFN, Sezione di Roma “Tor Vergata”, Via della Ricerca Scientifica 1, I-00133 Rome, Italy ,

    M. Casolino, M. P. De Pascale, N. De Simone, V. Di Felice, V. Malvezzi, L. Marcelli, S. Orsi, P. Picozza & R. Sparvoli

  12. IFAC, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Florence, Italy ,

    G. Castellini

  13. Department of Physics, University of Rome “Tor Vergata”, Via della Ricerca Scientifica 1, I-00133 Rome, Italy,

    M. P. De Pascale, N. De Simone, V. Di Felice, P. Picozza & R. Sparvoli

  14. Moscow Engineering and Physics Institute, Kashirskoe Shosse 31, RU-11540 Moscow, Russia ,

    A. M. Galper, L. Grishantseva, S. V. Koldashov, A. Leonov, V. V. Mikhailov, S. A. Voronov, Y. T. Yurkin & V. G. Zverev

  15. Universität Siegen, D-57068 Siegen, Germany

    W. Menn & M. Simon

  16. Department of Physics and The Oskar Klein Centre for Cosmoparticle Physics, KTH, AlbaNova University Centre, SE-10691 Stockholm, Sweden

    M. Pearce

  17. INFN, Laboratori Nazionali di Frascati, Via Enrico Fermi 40, I-00044 Frascati, Italy ,

    M. Ricci

Authors
  1. O. Adriani

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  2. G. C. Barbarino

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  3. G. A. Bazilevskaya

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  4. R. Bellotti

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  5. M. Boezio

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  6. E. A. Bogomolov

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  7. L. Bonechi

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  8. M. Bongi

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  9. V. Bonvicini

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  10. S. Bottai

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  11. A. Bruno

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  12. F. Cafagna

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  13. D. Campana

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  14. P. Carlson

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  15. M. Casolino

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  16. G. Castellini

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  17. M. P. De Pascale

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  18. G. De Rosa

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  19. N. De Simone

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  20. V. Di Felice

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  21. A. M. Galper

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  22. L. Grishantseva

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  23. P. Hofverberg

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  24. S. V. Koldashov

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  25. S. Y. Krutkov

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  26. A. N. Kvashnin

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  27. A. Leonov

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  28. V. Malvezzi

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  29. L. Marcelli

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  30. W. Menn

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  31. V. V. Mikhailov

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  32. E. Mocchiutti

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  33. S. Orsi

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  34. G. Osteria

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  35. P. Papini

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  36. M. Pearce

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  37. P. Picozza

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  38. M. Ricci

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  39. S. B. Ricciarini

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  40. M. Simon

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  41. R. Sparvoli

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  42. P. Spillantini

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  43. Y. I. Stozhkov

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  44. A. Vacchi

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  45. E. Vannuccini

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  46. G. Vasilyev

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  47. S. A. Voronov

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  48. Y. T. Yurkin

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  49. G. Zampa

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  50. N. Zampa

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  51. V. G. Zverev

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Corresponding author

Correspondence toP. Picozza.

Supplementary information

Supplementary Information

This file contains Supplementary Figures s1-s7 with Legends, Supplementary Methods, Supplementary Data and Supplementary References (PDF 324 kb)

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Adriani, O., Barbarino, G., Bazilevskaya, G.et al. An anomalous positron abundance in cosmic rays with energies 1.5–100 GeV.Nature458, 607–609 (2009). https://doi.org/10.1038/nature07942

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Editorial Summary

A hint of dark matter?

Cosmic ray positrons are known to be produced in interactions in the interstellar medium. As well as originating from this 'secondary source', positrons might also be generated in primary sources such as pulsars and microquasars — or by dark matter annihilation. A new measurement of the positron fraction in the cosmic radiation for the energy range 1.5–100 GeV has been made using data from the PAMELA satellite experiment. Previous measurements, made predominantly by balloon-borne instruments, yield a positron fraction compatible with 'secondary source' production from interactions between cosmic ray nuclei and interstellar matter. Above 10 GeV the new measurements deviate significantly from this expectation, pointing to the presence of a primary source, either a nearby astrophysical object or dark matter particle annihilations.

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