Abstract
The ANAIS (Annual modulation with NaI(Tl) Scintillators) experiment aims at the confirmation or refutation of the DAMA/LIBRA positive annual modulation signal in the low energy detection rate, using the same target and technique, at the Canfranc Underground Laboratory (LSC) in Spain. ANAIS-112, consisting of nine 12.5 kg NaI(Tl) modules produced by Alpha Spectra Inc. in a 3 times 3 matrix configuration, is taking data smoothly in “dark matter search” mode since August, 2017, after a commissioning phase and operation of the first detectors during the last years in various set-ups. A large effort has been carried out within ANAIS to characterize the background of sodium iodide detectors, before unblinding the data and performing the first annual modulation analysis. Here, the background models developed for all the nine ANAIS-112 detectors are presented. Measured spectra from threshold to high energy in different conditions are well described by the models based on quantified activities independently estimated following several approaches. In the region from 1 to 6~hbox {keV}_{{ee}} the measured, efficiency corrected background level is 3.58pm 0.02~hbox {keV}^{-1} , hbox {kg}^{-1} , hbox {day}^{-1}; NaI crystal bulk contamination is the dominant background source being ^{210}hbox {Pb}, ^{40}hbox {K}, ^{22}hbox {Na} and ^{3}hbox {H} contributions the most relevant ones. This background level, added to the achieved 1~hbox {keV}_{{ee}} analysis threshold (thanks to the outstanding light collection and robust filtering procedures developed), allow ANAIS-112 to be sensitive to the modulation amplitude measured by DAMA/LIBRA, and able to explore at three sigma level in 5 years the WIMP parameter region singled out by this experiment.
Highlights
Experimental efforts looking for Weakly Interacting Massive Particles (WIMPs), one of the preferred categories of the hypothetical dark matter particles our galactic halo should consist of in order to explain the Milky Way’s rotation curve, date back to the eighties of the last century; sensitivities have been continuously improving since profiting from the application of ultra-low background techniques in the building of the detectors, and the development of new detection schemes
The identification of the annual modulation in the detection rate is a signature of the scattering of the dark matter particles with the detector nuclei [16]; other experiments using different targets have not presented evidence of this effect [17,18,19], some hints were reported [20]
The background of all the nine detectors used in the ANAIS112 set-up has been thoroughly studied using the available data of the dark matter run, together with previous data taken at the smaller set-ups with the first detectors built
Summary
Experimental efforts looking for Weakly Interacting Massive Particles (WIMPs), one of the preferred categories of the hypothetical dark matter particles our galactic halo should consist of in order to explain the Milky Way’s rotation curve, date back to the eighties of the last century; sensitivities have been continuously improving since profiting from the application of ultra-low background techniques in the building of the detectors, and the development of new detection schemes. The identification of the annual modulation in the detection rate is a signature of the scattering of the dark matter particles with the detector nuclei [16]; other experiments using different targets have not presented evidence of this effect [17,18,19], some hints were reported [20]. A model-independent confirmation of the annual modulation positive signal reported by DAMA/LIBRA using the same target and technique, but different experimental conditions, is of utmost impor-. Following the first quantification of cosmogenic radionuclide production and its effects in NaI(Tl) crystals [41] and background assessment using data from the first ANAIS-112 modules produced by Alpha Spectra [42], a complete analysis and quantification of the different background components in the whole ANAIS-112 experiment is presented here.
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