Clarity in dark matter experiments

The experimental status of dark matter searches the last decade has always come down to one point of disagreement: do you believe that the DAMA/LIBRA signal is real or not. If you thought it was real, then you had to come up with dark matter models where a signal would be very apparent (8+ sigma) in DAMA/LIBRA but be non-existent in all the other more sensitive experiments (mostly utilising heavier atoms). If you thought it was not real, you had to really stretch to come up with possible causes that were not "poorly understood systematics" which is experimentalist for "they did not understand their experiment".

A quick note, the signal that DAMA/LIBRA claimed to see was an annual modulation in the very low energy (keV) nuclear recoils. This annual modulation could come from the earth passing through the dark matter halo, due to the alignment of the earth rotation around the sun and the sun rotation around the galaxy.

A new paper out on arxiv gives hypothesis where DAMA/LIBRA did not see a signal of dark matter, but also gives a source for the signal which is not due to a poorly understood systematic. While muons from cosmic rays had been considered as the source of the modulation, the peak from such a signal would be in the wrong place (the modulation would have the wrong phase). However, if the interaction rate of the muons from comic rays is similar to the interaction rate of the highest energy neutrinos from the sun, then the resulting modulation has a shift of phase which ends up being approximately the same as what you would expect from modulation due to dark matter. At the depth of DAMA/LIBRA, the interaction rates are similar.

This hypothesis fits the DAMA/LIBRA data as well as the dark matter hypotheses. Additionally, it fits the total set of direct dark matter searches and is not a claim that the DAMA/LIBRA experiment is poorly performed. These hypotheses can be differentiated and tested in future experiments; this will give direction for the field. And remove a major source of drama.

Those who want to read more can read the paper on the arxiv:

http://arxiv.org/abs/1407.1052