Analysis of backgrounds for the ANAIS-112 dark matter experiment

J. Amaré; S. Cebrián; I. Coarasa; C. Cuesta; E. García; M. Martínez; M. A. Oliván; Y. Ortigoza; A. Ortiz de Solórzano; J. Puimedón; A. Salinas; M. L. Sarsa; J. A. Villar; P. Villar

doi:10.1140/epjc/s10052-019-6911-4

2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2019) 79: 412
https://doi.org/10.1140/epjc/s10052-019-6911-4

Regular Article - Experimental Physics

Analysis of backgrounds for the ANAIS-112 dark matter experiment

J. Amaré¹^,2, S. Cebrián¹^,2^*, I. Coarasa¹^,2, C. Cuesta¹^,4, E. García¹^,2, M. Martínez¹^,2^,3, M. A. Oliván¹^,5, Y. Ortigoza¹^,2, A. Ortiz de Solórzano¹^,2, J. Puimedón¹^,2, A. Salinas¹^,2, M. L. Sarsa¹^,2, J. A. Villar¹^,2 and P. Villar¹^,2

¹ Laboratorio de Física Nuclear y Astropartículas, Universidad de Zaragoza, Calle Pedro Cerbuna 12, 50009, Zaragoza, Spain
² Laboratorio Subterráneo de Canfranc, Paseo de los Ayerbe s/n, 22880, Canfranc Estación, Huesca, Spain
³ Fundación Agencia Aragonesa para la Investigación y el Desarrollo, ARAID, Gobierno de Aragón, Avenida de Ranillas 1-D, 50018, Zaragoza, Spain
⁴ Present address: Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, CIEMAT, 28040, Madrid, Spain
⁵ Present address: Fundación CIRCE, 50018, Zaragoza, Spain

^* e-mail: scebrian@unizar.es

Received: 5 December 2018
Accepted: 3 May 2019
Published online: 15 May 2019

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 $3.58\pm 0.02~\hbox {keV}^{-1} \, \hbox {kg}^{-1} \, \hbox {day}^{-1}$ ; 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.