ANAIS: Status and prospects

TL;DR

ANAIS is an ongoing dark matter detection experiment using ultrapure NaI(Tl) scintillators aiming to confirm DAMA/LIBRA's positive signal through annual modulation analysis, with improved detector performance and radiopurity.

Contribution

This paper reports the current status, detector performance, radiopurity levels, and future prospects of the ANAIS experiment for dark matter detection.

Findings

High light collection efficiency (12-16 phe/keV) achieved.

Current crystals meet radiopurity goals for 232Th and 238U.

Identified and traced back to origin a 210Pb contamination issue.

Abstract

ANAIS (Annual modulation with NAI Scintillators) experiment aims to look for dark matter annual modulation with 250 kg of ultrapure NaI(Tl) scintillators at the Canfranc Underground Laboratory (LSC), in order to confirm the DAMA/LIBRA positive signal in a model-independent way. The detector will consist in an array of close-packed single modules, each of them coupled to two high efficiency Hamamatsu photomultipliers. Two 12.5 kg each NaI(Tl) crystals provided by Alpha Spectra are currently taking data at the LSC. These modules have shown an outstanding light collection efficiency (12-16 phe/keV), about the double of that from DAMA/LIBRA phase 1 detectors, which could enable reducing the energy threshold down to 1 keVee. ANAIS crystal radiopurity goals are fulfilled for 232Th and 238U chains, assuming equilibrium, and in the case of 40K, present crystals activity (although not at the required 20 ppb level) could be acceptable. However, a 210Pb contamination out-of-equilibrium has been identified and its origin traced back, so we expect it will be avoided in next prototypes. Finally, current status and prospects of the experiment considering several exposure and background scenarios are presented.