Letter to the Editor: Winstein and Zurek reply

  • Bruce Winstein and Kathryn M. Zurek, Kavli Institute for Cosmological Physics, The University of Chicago, Chicago, IL 60637, USA and Fermi National Accelerator Laboratory, Batavia, IL 60510, USA
Physics 2, 54
A Viewpoint commentary discussing recent results from the Fermi Gamma-Ray Telescope on cosmic rays from dark matter may have dismissed an unusual spectral feature too soon; the authors respond.

We agree with Martin Israel that, to resolve the discrepancy, both experiments need to work to be sure that the systematic uncertainties are correct. Still, we conclude that the evidence for a prominent feature in the spectrum has been cast in serious doubt. And since our Viewpoint appeared, the HESS team has released a measurement of the e+e- flux in the energy range 400 GeV – 5 TeV [1], overlapping with the Fermi result. HESS and Fermi agree (on the lack of a feature), each with very high statistical significance. It is possible that both HESS and Fermi have treated their systematics incorrectly, causing each to miss the feature observed by ATIC, but the evidence at this point is leaning in the direction of Fermi and now HESS: there is no prominent feature in the 400–800 GeV range. As Israel points out, the most crucial systematic uncertainties involve the behavior of the calorimeters, and those of Fermi and ATIC have relative strengths and weaknesses. Experiments with high statistics are generally better able to probe unforeseen systematic uncertainties than are those with low statistics. We, along with Israel, look forward to having these discrepancies resolved by the experiments in question.

References

  1. F. Aharonian et al., arXiv:0905.0105 (2009)

Recent Articles

Focus: Keeping a Secret for a Whole Day
Interdisciplinary Physics

Focus: Keeping a Secret for a Whole Day

Researchers have securely contained a single bit for a record 24 hours, during which it was inaccessible to both sender and recipient, a technology that could be useful for voting or bidding. Read More »

Synopsis: Proteins as Shock Absorbers
Biological Physics

Synopsis: Proteins as Shock Absorbers

Proteins in nerve cells function like shock absorbers that protect the cells from mechanical stress. Read More »

Viewpoint: Cosmic Clues from Mini Clumps of Dark Matter
Cosmology

Viewpoint: Cosmic Clues from Mini Clumps of Dark Matter

Searches for ultracompact clumps of cold dark matter have come up empty, but these nondetections place new limits on the early expansion history of the Universe. Read More »

More Articles