Thursday, December 17, 2009

CDMS results in a few hours!

As most of you know, there is a rumor about CDMS getting some of sort of signal from its dark matter search. Well, in a few hours we will know if all the fuzz around it was justified.

CDMS stands for cryogenic dark matter search. It is a solid state detector designed to "listen" the sound made by dark matter particles when they interact with the nucleus of the atoms in the detector. These interactions cause the nucleus to recoil, as a result of that the atoms in the detector (which are arranged in a lattice) vibrate and produce phonons (some sort of quanta of sound). This signal can be measured and used to detect the interactions of weak interacting particles.

Now, this is only a very simplified description of the experiment. The practical difficulties are huge. First of all, random thermal vibrations can wash away very easily any signal, so the detector must be kept at really low temperatures. Then, collisions with cosmic rays will also spark the detector as fireworks, for this reason the detector is located underground in a deep mine in Minessota. But, how about other "backgrounds" like nuclear decay of particles in the rocks surrounding the detector? Well, the study of systematic backgrounds is really an art. One way to calibrate the detector is to place it close to some radioactive source and use the signal gathered this way to callibrate the detector.

Early in the year, I saw the results of the CDMS collaboration and there was no signal (or hint of it), so it is hard to think that the results that are about to be announced will have 5-sigma signal (the usual threshold accepted as a detection), but maybe they got some sort of provocative signal at a smaller sigma level. Or maybe all the fuzz was just that, fuzz.

Anyway, we will know the answer in a few hours!


Anonymous said...

Not justified...generating so much buzz for a 1.epsilon `detection' is a black eye for the particle physics community.

Luis Sanchez said...

Yes, sorta much fuzz for little. But then, the fuzz came from people outside the cdms collaboration, so it is hard to blame them.