Wednesday, April 18, 2012

Dark-matter-exists general: our foes have found DM at 5.7 sigma, too

Remotely related breaking news: A team of Chilean astronomers behind the ESO telescope claims that there's no dark matter in the Solar System's vicinity. If true, the direct searches such as those described in the article below should be very hard.

One more: IceCube found too few neutrinos, causing trouble to the "proton acceleration" theory of the gamma ray bursts' origin.
This blog regularly covers the newest developments in the ongoing war on existence of the dark matter. In some sense, yesterday's proposed 130 GeV gamma-ray line glimpsed by Fermi may be another salvo in the war but when I talk about the war, I mainly talk about the direct searches that try to detect the collisions of dark matter with our nuclear matter.

CDMS' bombs

In one way or another, the coalition of the willing that claims "dark matter is seen" (DMIS) has been helped by numerous experiments, especially DAMA/LIBRA, PAMELA, CoGeNT, CRESST-II, and perhaps Fermi. The "dark matter isn't seen" (DMINS) axis forms around CDMS and XENON10/100.

What is new at the battlefront?

In normal wars, one uses his own bombs to destroy the enemy. However, Juan Collar of CoGeNT, a general of the DMIS forces, together with N. E. Fields did something else. They used their enemies' own bombs against them. The new preprint is called
A Maximum Likelihood Analysis of Low-Energy CDMS Data
They invaded the data of their key enemy, the CDMS experiment from DMINS, and found a bombshell over there. At least, Collar and Fields think that what they found is a bomb whose detonation power is 5.7 sigma standard deviations.

They tried to model the CDMS' low-energy data, especially those in the nuclear recoil band, and compared two models to describe these data. The model with an extra exponentially distributed component is heavily favored over "no dark matter" null hypothesis, they claim, and this preference may be quantified as 5.7 sigma.

Collar and Fields give some brief reasons why the neutron scattering shouldn't be the right explanation for the excess. They believe that with this finding, the properties of the hypothetical weakly interacting massive particle (WIMP) are compatible with those seen in the DMIS experiments.

They propose to conquer CDMS that would become a protectorate of DMIS and they encourage the members of CDMS to keep on learning basic things on backgrounds, detectors, energy scales, and the multiplication table up to 10 × 10. While the mere counting of papers and collaborations suggests that they must be seeing dark matter, many people remain extremely skeptical. While many results in the DMIS coalition may look remotely compatible with each other, don't try to overlook their significant differences (Figure 4 in the Collar-Fields paper) and the fact that the WIMP mass is claimed to be around 10 GeV (or 7-20 GeV), well below 130 or 144 GeV suggested by the Fermi's gamma-ray line (and by the sensible SUSY phenomenology, too).

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