Dark Matter implications of DAMA/LIBRA-phase2 results

Abstract

Recently, the DAMA/LIBRA collaboration released updated results from their search for the annual modulation signal from Dark Matter (DM) scattering in the detector. Besides approximately doubling the exposure of the DAMA/LIBRA data set, the updated photomultiplier tubes of the experiment allow a lower recoil energy threshold of 1\,keV electron equivalent compared to the previous threshold of 2 keV electron equivalent. We study the compatibility of the observed modulation signal with DM scattering. Due to a conspiracy of multiple effects, the new data at low recoil energies is very powerful for testing the DM hypothesis. We find that canonical (isospin conserving) spin-independent DM-nucleon interactions are no longer a good fit to the observed modulation signal in the standard halo model. The canonical spin-independent case is disfavored by the new data, with best fit points of a DM mass of $\sim 8\,$GeV, disfavored by $5.2\,\sigma$, or a mass of $\sim 54\,$GeV, disfavored by $2.5\,\sigma$. Allowing for isospin violating spin independent interactions, we find a region with a good fit to the data with suppressed effective couplings to iodine for DM masses of $\sim 10\,$GeV. We also consider spin-dependent DM-nucleon interactions, which yield good fits for similar DM masses of $\sim 10\,$GeV or $\sim 45\,$GeV