New Paper on Resolving the DAMA/LIBRA Controversy

The KIMS collaboration has a new paper out on looking at nuclear vs electron recoil discrimination using pulse shape analysis in NaI(Tl) crystals. This work looks interesting because NaI is what is used by DAMA/LIBRA in their papers reporting an annually modulating signal that looks like what might be expected from dark matter.

The paper notes that particle discrimination has traditionally been much more difficult in NaI compared to other crystals like CsI(Tl), which is used in most other work by KIMS. No one else has been able to measure the DAMA signal, but various groups have been investigating using NaI detectors to see if they see the same thing. Particle discrimination could be a powerful tool since it can be used to significantly reduce the number of electron events in the data set. In most models, dark matter scatters elastically off nuclei but has an insignificant cross section with electrons.

The analysis here uses a simple pulse shape analysis looking at the “mean decay time” of the pulse, which is somewhat different for electrons compared to nuclei. The difference is quite noticeable by around 3 keV but is still present even in the 1-2 keV energy range. They find that the crystals used in the paper are now even better than CsI at pulse shape discrimination.

The most important thing in the paper comes at the end: a full scale experiment based on the technologies used in the paper could potentially rule out the DAMA/LIBRA signal in as little as a year. Given that DAMA/LIBRA has been reporting a possible dark matter signal for a decade, this might be a great way to resolve the debate for good.