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XENON100 is certain about its uncertainty

Part of the XENON100 experiment (Courtesy: XENON100 collaboration)

By Hamish Johnston

Is the XENON100 collaboration in the dark about dark matter, or will its critics see the light? The latest installment of this debate has appeared on the arXiv preprint server.

On 6 May Jon Cartwright reported on a furore that has broken out in the dark-matter detection community.

Earlier that week the XENON100 collaboration posted a preprint with an analysis of the first experimental results from its dark-matter detector. It didn’t see any of the dark stuff, which means that the positive sightings reported by two other experiments (DAMA and CoGeNT) could be false.

But then two US-based physicists – Juan Collar and Dan McKinsey — posted a preprint that took XENON100 physicists to task on their analysis of the data. In particular, Collar and McKinsey believe that the XENON100 team is overconfident about how it extrapolated the known response of the detector to high-energy particles to lower energies – where the response is unknown.

This low-energy response is crucial because that is where XENON100, DAMA and CoGeNT have all looked for dark matter.

Now, XENON100 has responded with yet another preprint defending its analysis and claiming that it has “properly taken into account the uncertainty” in the low-energy response.

I can’t wait for the next preprint in this dark-matter “he said, she said”!

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  1. John Duffield

    This is getting unseemly, and it’s turning into more than just a spat. The Xenon guys have got the honesty to report a null result, and the other guys just won’t have it. And yet everybody can read The Foundation of the General Theory of Relativity and look at page 185 where Einstein says “the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy”. This is spatial energy, it is not in the form of particles. And it’s a reminder that a non-uniform energy distribution results in gravity, and that matter only causes gravity because of the energy content. Are we to ignore relativity? Are we to ignore Einstein’s 1920 Leyden Address where he described a gravitational field as inhomogeneous space? Are we to ignore the raisins-in-the-cake analogy of the expanding universe, wherein the space between the galaxies expands, but not within? The obvious result of this, is inhomogeneous space, a halo of it around each and every galaxy. That’s a gravitational field, just the thing to cause flat galactic rotation curves, only there isn’t any matter on the end of it. Not in the usual sense. Because space isn’t nothing, it has its vacuum energy. This has a mass-equivalence. And look up to the clear night sky. Space, is dark.

  2. The finding may imply that cold dark matter does not exist. A credible new scenario already exist. It appears that lensing data of a galaxy cluster can be modeled by 1.5 eV neutrinos. So the most obvious dark matter candidate is back in business. To have to some 20% dark matter, the right handed (sterile) modes should be occupied too, due to a meV Majorana mass matrix, next to the 1.5 eV Dirac matrix. Another important point is that dark matter is not (!!!) needed for large scale structure formation, because gravitational hydrodynamics explains hitherto overlooked structure formation due to viscosity, in a top-down scenario. So the most modest scenario is back on the table, just neutrinos and a better hydrodynamics. The mass of the electron anti neutrino will be measured in Katrin 2015. The gravitational hydrodynamics already explains many features such as size of cosmic voids, flattening of rotation curves, the Tully Fisher relation as well as various observed events in microlensing and radio.


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