Improved dark matter limits from pulse shape discrimination in a low background sodium iodide detector at the Boulby mine

Analysis of alpha-emitting isotopes in an inorganic scintillator

“…Not only are the many X-rays in the actinide decay chains a serious lowenergy background; equally importantly, the characteristic signature of a WIMP interaction is the scintillation pulse pro"le of the recoil nucleus. Comparison [4] of neutron-induced recoils and gamma rays shows that recoil nuclei, though of much lower energy, have pro"les quite similar to alpha pulses.…”

“…A preliminary account has been given by Barton [6]. The technique has been applied to scintillating crystals prepared for the UK Dark Matter Collaboration [4] and subsequently extended to include study of time-correlated pulses and hence obtain quantitative information about non-equilibrium in the actinide decay chains. Most of this work has been carried out using a large (3.6 kg) single crystal of NaI(Tl) grown and encapsulated by Quartz et Silice.…”

First results from dark matter search experiment with LiF bolometer at Kamioka underground laboratory

“…5, the allowed regions for the (a): sufficiently light WIMPs for which 127 I loses the sensitivity and NaI effectively becomes a detector with one nuclide, (b): WIMPs with mass near the center value of DAMA's annual modulation signal, and (c): WIMPs heavy enough for which 23 Na and 127 I both have good sensitivities, are shown. In the three plots, the limits from Na and I of UKDMC [10] are shown in dotted and dash-dotted lines, respectively, NaI combined limits of UKDMC [10] are shown in thin solid lines and LiF combined limits from this work are shown in thick solid lines. UKDMC published the recalculated data [14] in which only NaI combined limits are shown, and we derived the limits in the a p − a n plane on the assumption that the sensitivity ratios of 23 Na and 127 I are the same as those shown in Ref.…”

“…3[4]. Instead, we compared our results with those of the UKDMC experiments [10,14]. Since UKDMC shows the limits from 23 Na and 127 I independently [10], we can calculate the limits in the a p − a n plane from 23 Na and 127 I and combine them without any assumptions.…”

“…Instead, we compared our results with those of the UKDMC experiments [10,14]. Since UKDMC shows the limits from 23 Na and 127 I independently [10], we can calculate the limits in the a p − a n plane from 23 Na and 127 I and combine them without any assumptions. It should be noted that limits in the a p − a n plane from the NaI detector are largely affected by the sensitivity ratio of 23 Na and 127 I; the threshold of the detector and the quenching factor of 127 I largely change the limits.…”