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Week of June 6, 2010

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"An anomalous positron abundance in cosmic rays with energies 1.5-100 GeV," by O. Adriani and 50 others, Nature, 458(7238): 607-9, 2 April 2009.

[Author's affiilations: 16 institutions worldwide]

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 medium, which is referred to as a 'secondary source'. Positrons might also originate in objects such as pulsars and microquasars or through dark matter annihilation, which would be 'primary sources'. Previous statistically limited measurements 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. 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."

This 2009 report in Nature was cited 35 times in current journal article indexed by Clarivate Analytics during January-February 2010. Only two other physics papers published in the last two years, aside from reviews, attracted higher citation counts during that two-month period. Prior to the most recent bimonthly count, citations to the paper have accrued as follows:

November-December 2009: 28 citations
September-October 2009: 68
July-August 2009: 35
June-July 2009: 18

Total citations to date: 184

SOURCE: Hot Papers Database (Included with a subscription to the print newsletter Science Watch®, available from the Research Services Group of Thomson Reuters. Packaged on a CD that is mailed with each Science Watch issue, the Hot Papers Database contains data on hundreds of highly cited papers published during the last two years. User interface permits searching by author, organization, journal, field, and more. Total citations, as well as citations accrued during successive bimonthly periods, can be assessed and graphed. An updated CD containing the most recent bimonthly data is mailed with every new issue of Science Watch, six times a year. The CD also includes an electronic version of the Science Watch issue in HTML format, for personal desktop access.


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