Study of the energy calibration of the DEAP-3600 detector using Na-22 source data and simulations

TL;DR

This work addresses the challenge of calibrating the energy response of the DEAP-3600 liquid-argon detector without contaminating the active target by using an external $^{22}$Na source deployed around the detector. A three-gamma tagging scheme with nearby LYSO detectors and RAT-based Monte Carlo simulations is employed to compare data and simulations, focusing on the energy spectrum and the detector's light yield. The analysis reveals that MC spectra require a modest energy shift, corrected by a factor of $1.03$, to align with data, and yields a per-position average light yield of $6.15 \pm 0.02$ PE/keV. The results validate the MC-based energy calibration approach and establish a reliable, position-dependent energy scale for the DEAP-3600 dark matter search.</nobr>

Abstract

DEAP--3600 is a single--phase liquid argon (LAr) direct--detection dark matter experiment operating 2~km underground at SNOLAB (Sudbury, Canada). The detector consists of 3.3~tons of LAr contained in a spherical acrylic vessel. At a WIMP mass of 100~GeV, DEAP--3600 has a projected sensitivity of $10^{-46}\,\mathrm{cm}^{2}$ for the spin--independent elastic scattering cross section of WIMPs. Radioactive sources have been used for the energy calibration and to test the detector performance. One of the most effective calibration runs has been taken with a $^{22}\mathrm{Na}$ source deployed in a tube located around the DEAP--3600 steel shell. The simultaneous emission of three $γ$'s by the source provides an excellent tagging for the $^{22}\mathrm{Na}$ decay. The results concerning the energy response of the detector and the agreement between data and Monte Carlo simulations in DEAP--3600 are investigated in this study.

Figures (4)

• Figure 1: The CAL F calibration tube outside the outer steel shell in DEAP-3600.
• Figure 2: Energy spectrum in LAr for different tagging configurations for position 1.
• Figure 3: Data (black) and MC (red) energy spectra for single tag events for position 1: Figure (a) shows the spectra before any correction applied; Figure (b) shows the spectra after the correction.
• Figure 4: On the left: fits performed on the 511 keV and 1.27 MeV peaks; on the right: a zoom of the fit on 511 keV peak.