14 March 2011

The Search For Dark Matter Continues

On Wednesday, the Xenon 100 experiment will report its new experimental boundaries on the mass and interaction scale of possible directly detectable dark matter particles. The trouble is that the experimental boundaries have been tightening since the 1980s and there is still no good evidence of any "signal" of a directly detected dark matter particle.

The most appealing possibility – a weak scale dark matter particle interacting, like neutrinos, via Z-boson exchange - leads to the cross section of order 10^-37 cm^2 which has been excluded in the 80s. There exists another natural possibility for WIMP dark matter: a particle interacting via Higgs boson exchange. This would lead to the cross section in the ballpark of 10^-43cm^2 (however strongly depending on the Higgs mass, and also on the coupling of dark matter to the Higgs) which is currently being probed by experiment.

If Xenon100 see nothing, it is a good moment to seriously start worrying whether the WIMP paradigm corresponds to reality, although models that predict even lower cross sections do exist. In the worst case dark matter may be very weakly interacting (axions, gravitinos) or very light (keV-MeV scale dark matter), in which case the direct detection searches are doomed from the start.

For the next decade or so the direct detection will go in the direction of monster detectors that will allow us to improve the sensitivity down to 10^-47 cm^2. Preparations for a 1 ton xenon detector are already well underway, while 10 ton xenon detectors are on the drawing board. Actually, it’s not the size of the experiment that is the limit here. When the sensitivity reaches 10^-48cm^2, probably sometime in the next decade, these searches will encounter the background of atmospheric neutrinos and diffuse supernova neutrinos. Thus, asymptotically, dark matter detection will merge into neutrino physics[.]

Current boundaries suggest islands of possibility around 10 GeV mass and 80 GeV mass. There are no rumors of ground breaking new discoveries, but are rumors that results from Xenon 100 may be delayed due to difficulties in data analysis.


Peter Fred said...

"If Xenon100 sees nothing, it is a good moment to seriously start worrying whether the WIMP paradigm corresponds to reality"

I have experiments that raise questions about both the dark matter and the dark energy ideas. They imply that luminosity rather is the source of gravitational attraction. A different times test masses have been placed test masses between a 1000 W hot source and containers filled with ice water. After 4 or 5 minutes of impressed power, the weight of these test masses as measured by a thermally isolated force sensor was observed to increase by 1.9%, 8.9%, 9.6% and 16% respectively. Scientist have unhesitantly assumed for 300 years that some yet-to-be-specified, inherent, mysterious property of mass can either warp space or attract mass. If anyone ever bothers to think about it, the assumption that luminosity is the source of gravitation is much more reasonable and plausible than that mass is the source. Luminosity decreases inversely as the square of the distance from the source as does the force of gravity. Furthermore, it is luminosity that is interchanged between gravitationally bound objects such as binary stars, satellites of stars, galaxies and clusters. See my paper for my experiments and a for a plausible solution to the flat rotation curves and cosmic acceleration. http://vixra.org/abs/0907.0018

Andrew Oh-Willeke said...

If luminosity is the source of gravity, how do you explain planetary gravity, which is experimentally established, or the bullet cluster?

Similarly, how do you explain GR gravitational effects?

This is not to diss your experiments. An experimental effect always has to be explained. But, to fit with the data that confirms a current theory that seems mass-energy as the source of gravitational attraction, you have to have a theory that fits all that facts which is simple luminosity model does not.

Peter Fred said...

Planetary data is the easiest to explain with a luminosity-based theory.
The amount of luminosity leaving the sun varies as (10^26 W)/R^2 where R is the distance from the sun. A cross section of this luminosity is absorbed by every planet which is given by pi*r^2 where r is the radius of the planet. My experiments imply that this luminosity is slightly gravitationally attractive. If this is so,then there will be a difference between the planet's dayside surface gravity and its nightside surface gravity. This difference will in turn produce a pressure difference at the planets center. An estimate for the pressure at the center of the planet is given by P =g*rho*r where P is the pressure at the center, g is the surface gravity, rho the density of the planet and r the radius of the planet. Let delta g*rho*r equal the pressure difference between the the opposite hemispheres of the planet. The night side hemisphere will exert a greater force than the day side hemisphere producing a net force directed towards the sun. The product (delta g*rho*r) * (pi*r^2) represents the force that the night side hemisphere exerts on the dayside hemisphere. Plugging in the numbers will get a value of delta g that is within an order of magnitude of the 0.006 m/s^2 needed to centripetally accelerate the earth towards the sun. This is better explained in my paper which no body bothers to read. If anyone ever goes there I hope he or she will also see the graph that shows the close coincidence between the “dimming of the universe” and the onset of "cosmic acceleration". Even if the dark matter is found it will not be able to explain "cosmic acceleration" in a simple and plausible way as my luminosity-based gravity theory. I thought experiments would trump theory even if they are inexpensive table top experiments. But what do I know.