The intriguing signal from the DAMA/LIBRA experiment in Italy has been ruled out as a sign of "normal" dark matter, according to new experimental data by the CoGeNT collaboration.
The DAMA results have long been controversial but the newest result shows an unequivocal sign of something-it's just not clear what that something is and whether it is dark matter. Other dark matter searches have ruled out the kinds of dark matter particles that are consistent with the DAMA results, piece by piece, but there was always an opening for very light dark matter particles.
The CoGeNT results, along with results from the COUPP bubble chamber experiment (more on COUPP in the upcoming print issue of symmetry), rule out the possibility of there being very light dark matter particles spread about in a galactic halo, the "normal" kind of dark matter that is usually proposed, and that would have led to the kind of signal that DAMA/LIBRA observed.
However, the authors of the paper presenting the CoGeNT results point out that there could be some particularly exotic form of dark matter such as axions, Q-balls, or particles predicted by some of the more complicated versions of supersymmetry.
Experiments designed for neutrino detection, such as MAJORANA, should be able to look for some of those exotic dark matter candidates.
All this leaves open the question: "What did DAMA really see?" It now appears unlikely that it was dark matter but there are no other convincing explanations.
