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 1keV electron equivalent compared to the previous threshold of 2keV 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 ∼8GeV, disfavored by 5.2σ, or a mass of ∼54GeV, disfavored by 2.5σ. 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 ∼10GeV. We also consider spin-dependent DM-nucleon interactions, which yield good fits for similar DM masses of ∼10GeV or ∼45GeV.