DarkSide Document 2445-v1

The DarkSide-50 Experiment: Electron Recoil Calibrations and A Global Energy Variable

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Brianne R. Hackett
Updated by:
Brianne R. Hackett
Document Created:
09 Jan 2018, 17:46
Contents Revised:
09 Jan 2018, 17:46
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10 Feb 2018, 13:41
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Over the course of decades, there has been mounting astronomical evidence for non-baryonic dark
matter, yet its precise nature remains elusive. A favored candidate for dark matter is the Weakly
Interacting Massive Particle (WIMP) which arises naturally out of extensions to the Standard
Model. WIMPs are expected to occasionally interact with particles of normal matter through
nuclear recoils. DarkSide-50 aims to detect this type of particle through the use of a two-phase
liquid argon time projection chamber. To make a claim of discovery, an accurate understanding
of the background and WIMP search region is imperative. Knowledge of the backgrounds is done
through extensive studies of DarkSide-50’s response to electron and nuclear recoils.
The CALibration Insertion System (CALIS) was designed and built for the purpose of introducing radioactive sources into or near the detector in a joint effort between Fermi National Laboratory
(FNAL) and the University of Hawai’i at M¯ anoa. This work describes the testing, installation, and
commissioning of CALIS at the Laboratori Nazionali del Gran Sasso. CALIS has been used in multiple calibration campaigns with both neutron and γ sources. In this work, DarkSide-50’s response
to electron recoils, which are important for background estimations, was studied through the use
of γ calibration sources by constructing a global energy variable which takes into account the anticorrelation between scintillation and ionization signals produced by interactions in the liquid argon.
Accurately reconstructing the event energy correlates directly with quantitatively understanding
the WIMP sensitivity in DarkSide-50.
This work also validates the theoretically predicted β decay spectrum of 39Ar against 39Ar β
decay data collected in the early days of DarkSide-50 while it was filled with atmospheric argon;
a validation of this type is not readily found in the literature. Finally, we show how well the
constructed energy variable can predict energy spectra for the calibration sources and for 39Ar.
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