Background analysis and status of the ANAIS dark matter project

TL;DR

ANAIS is a NaI(Tl) dark matter detection project at Canfranc aiming to verify DAMA/LIBRA's annual modulation signal, with recent prototypes achieving low background and promising low energy thresholds.

Contribution

The paper reports background modeling, radiopurity achievements, and initial results of improved detectors for the ANAIS dark matter experiment.

Findings

Radiopurity goals for Th-232 and U-238 achieved

Pb-210 contamination identified and studied

Prototype detectors show potential for ~1 keVee energy threshold

Abstract

ANAIS (Annual modulation with NaI Scintillators) is a project aiming to set up at the new facilities of the Canfranc Underground Laboratory (LSC), a large scale NaI(Tl) experiment in order to explore the DAMA/LIBRA annual modulation positive result using the same target and technique. Two 12.5 kg each NaI(Tl) crystals provided by Alpha Spectra took data at the LSC in the ANAIS-25 set-up. The comparison of the background model for the ANAIS-25 prototypes with the experimental results is presented. ANAIS crystal radiopurity goals have been achieved for Th-232 and U-238 chains, but a Pb-210 contamination out-of-equilibrium was identified, whose origin has been studied. The high light collection efficiency obtained with these prototypes allows to anticipate an energy threshold of the order of 1 keVee. A new detector, with improved performances, was received in March 2015 and very preliminary results are shown.