Tuesday, June 12, 2012

Fermi \(130\GeV\) line claimed to reach 5 sigma

Evidence for WIMP dark matter could have gotten strong

Christoph Weniger's observation of a gamma-ray line in the Fermi photographs of the galaxy has ignited some activity in the astroparticle physics boundary.

In eight weeks, the paper has collected 20 citations. Most of the followups tend to be positive; some papers prefer to claim that "nothing can be seen here". The list of mostly negative papers includes a report by the Fermi collaboration itself.

The newest paper (an astro-ph paper that is one week old)
Strong Evidence for Gamma-ray Lines from the Inner Galaxy
was written by Meng Su and Douglas P. Finkbeiner who are Harvard- and Harvard-Smithsonian-affiliated – and seem kind of trustworthy to me for various reasons. In particular, they're two of the four people who found the Fermi bubbles, see the picture above.

In the new paper, Finkbeiner and Su claim that the line near \(130\GeV\) has a significance of 5.0 sigma, exceeding the previous estimates. With some dilution of the probability, they stand at 3.7 sigma but even this figure could reach 5 sigma by the end of 2013.

The authors also say that a pair of lines, near \(110\) and \(130\GeV\), could provide us with a slightly better fit than a single line although the one-line description isn't bad at all. Even more interestingly, they say that the pair of lines could be compatible with the Higgs in space paradigm.

In that 2009-2010 paper, it was conjectured that the dark matter particles, the WIMPs, may annihilate to \(\gamma Z\), something that e.g. Gordon Kane and others consider the most likely decay channel, but also to \(\gamma h\) where \(h\) is the Higgs boson. The kinematics is compatible with the idea that the two lines come exactly from these two decay channels, using the usual estimates for the masses \(90+\), \(130-\), and \(140+\GeV\) for the Z-boson, Higgs boson, and the WIMP, respectively.

If these lines – and both of them – got indeed stronger and if their energies continued to match the predictions from the decays, it would be quite a galactic test for particle physics, relativistic kinematics, and the masses of the particles originally extracted from the terrestrial colliders.

I think it's clear that not only because of the LHC, we have entered a new era dominated by the experimental data. I don't remember we could have gotten excited by such experimental hints just a few years ago. Of course, most of such hints will go away but some of them may stay with us which would be exciting, indeed.

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