Speaker
Description
ANAIS (Annual modulation with NaI Scintillators) is a direct dark matter detection experiment whose goal is to confirm or refute in a model independent way the highly controversial positive annual modulation signal reported by DAMA/LIBRA collaboration for more than twenty cycles. ANAIS-112, consisting of 112.5 kg of NaI(Tl) scintillators, is presently in data taking phase at the Canfranc Underground Laboratory, in Spain, since August 2017. The dark matter interpretation of the modulation signal depends critically on a complete understanding of the detector response to nuclear recoils, which are expected to be induced via elastic scattering of dark matter particles off target nuclei in many of the models considered for such dark matter particles. It is well known that the light output from nuclear recoils is reduced with respect to electrons depositing an equivalent energy by the quenching factor, a parameter which is actually not well known for NaI(Tl) scintillators. Not only recent measurement on the quenching factor of sodium showed significantly different results, but also very few measurements on the quenching factor of iodine have been performed up to now. This magnitude is usually determined by measurements in a monoenergetic neutron beam, requiring small scintillating crystals to avoid multiple scattering. On the other hand, the study presented here relies on a different approach, aiming at the evaluation of the quenching factor by exposing directly the large ANAIS-112 crystals to neutrons from a Cf-252 source. For this purpose, detailed Monte Carlo simulations of the full experimental set-up are required, which should be checked against the experimental measurement. Comparison between measurement and simulation allows testing different quenching factor models and following a best-fit strategy. Moreover, this simulation could be also exploited to improve the ANAIS-112 event selection procedure, helping to identify nuclear recoils-dominated regions and to design an efficiency calibration procedure.
