Designing and testing the neutron source deployment system and calibration plan for a dark matter detector

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, June 2011."June 2010." Cataloged from PDF version of thesis.Includes bibliographical references (p. 113-116).In this thesis, we designed and tested a calibration and deployment system for the MiniCLEAN dark matter detector. The deployment system uses a computer controlled winch to lower a canister containing a neutron source into the detector where the neutron source pulses to produce calibration data. The winch then pulls the neutron source back out of the detector. We found that the deployment system position is precise to under 0.05 cm, one tenth of the minimum required precision. We designed a canister that will hold the neutron source during the calibration process. The canister will contain a dielectric gel to thermally and electrically insulate the high voltage electronics and the neutron source from the rest of the detector. We calculated the equilibrium temperature change of the calibration neutron source when it is turned on and found that the temperature increases by 92.6+isi K, corresponding to a rise in the dielectric gel height of 1.501i.9 cm. This temperature change is within the service temperature range of the dielectric gel; however, a more thermally conductive gel could still be used to reduce the temperature increase. We simulate the background external neutrons in MiniCLEAN and find that the addition of an air-filled calibration tube to the basic MiniCLEAN design has little effect on the external neutron background rate. Lastly, we simulate the calibration process in order to determine how long we must calibrate MiniCLEAN in order to obtain the desired 5% statistical precision on measurements of the calibration neutron-induced recoil spectrum. We found that a minimum of 2.48x 106 neutrons are needed to measure the total counts in the region of interest in energy to 5% (corresponding to a pulse mode calibration time of 124 seconds assuming that neutrons are produced at a rate of 105 per second), and 2.02x 107 neutrons are needed to achieve 5% measurements of the energy spectrum with 2 KeVee binning in the region of interest (corresponding to a time of 1005 seconds).by Shawn Westerdale.S.B

Scintillation efficiency measurement of Na recoils in NaI(Tl) below the DAMA/LIBRA energy threshold

The dark matter interpretation of the DAMA modulation signal depends on the NaI(Tl) scintillation efficiency of nuclear recoils. Previous measurements for Na recoils have large discrepancies, especially in the DAMA/LIBRA modulation energy region. We report a quenching effect measurement of Na recoils in NaI(Tl) from 3keV$_{\text{nr}}$ to 52keV$_{\text{nr}}$, covering the whole DAMA/LIBRA energy region for light WIMP interpretations. By using a low-energy, pulsed neutron beam, a double time-of-flight technique, and pulse-shape discrimination methods, we obtained the most accurate measurement of this kind for NaI(Tl) to date. The results differ significantly from the DAMA reported values at low energies, but fall between the other previous measurements. We present the implications of the new quenching results for the dark matter interpretation of the DAMA modulation signal

A Study of Nuclear Recoil Backgrounds in Dark Matter Detectors

Despite the great success of the Standard Model of particle physics, a preponderance of astrophysical evidence suggests that it cannot explain most of the matter in the universe. This so-called dark matter has eluded direct detection, though many theoretical extensions to the Standard Model predict the existence of particles with a mass on the 1–1000 GeV scale that interact only via the weak nuclear force. Particles in this class are referred to as Weakly Interacting Massive Particles (WIMPs), and their high masses and low scattering cross sections make them viable dark matter candidates. The rarity of WIMP-nucleus interactions makes them challenging to detect: any background can mask the signal they produce. Background rejection is therefore a major problem in dark matter detection. Many experiments greatly reduce their backgrounds by employing techniques to reject electron recoils. However, nuclear recoil backgrounds, which produce signals similar to what we expect from WIMPs, remain problematic. There are two primary sources of such backgrounds: surface backgrounds and neutron recoils. Surface backgrounds result from radioactivity on the inner surfaces of the detector sending recoiling nuclei into the detector. These backgrounds can be removed with fiducial cuts, at some cost to the experiment’s exposure. In this dissertation we briefly discuss a novel technique for rejecting these events based on signals they make in the wavelength shifter coating on the inner surfaces of some detectors. Neutron recoils result from neutrons scattering off of nuclei in the detector. These backgrounds may produce a signal identical to what we expect from WIMPs and are extensively discussed here. We additionally present a new tool for calculating (α, n) yields in various materials. We introduce the concept of a neutron veto system designed to shield against, measure, and provide an anti-coincidence veto signal for background neutrons. We discuss the research and development that informed the design of the DarkSide-50 boron-loaded liquid scintillator neutron veto. We describe the specific implementation of this veto system in DarkSide-50, including a description of its performance, and show that it can reject neutrons with a high enough efficiency to allow DarkSide-50 to run background-free for three years

Snowmass2021 cosmic frontier white paper: Ultraheavy particle dark matter

We outline the unique opportunities and challenges in the search for "ultraheavy" dark matter candidates with masses between roughly 10 TeV and the Planck scale $m_{\rm pl} ≈ 10^{16}$ TeV. This mass range presents a wide and relatively unexplored dark matter parameter space, with a rich space of possible models and cosmic histories. We emphasize that both current detectors and new, targeted search techniques, via both direct and indirect detection, are poised to contribute to searches for ultraheavy particle dark matter in the coming decade. We highlight the need for new developments in this space, including new analyses of current and imminent direct and indirect experiments targeting ultraheavy dark matter and development of new, ultra-sensitive detector technologies like next-generation liquid noble detectors, neutrino experiments, and specialized quantum sensing techniques

Snowmass2021 Cosmic Frontier White Paper: Ultraheavy particle dark matter

We outline the unique opportunities and challenges in the search for "ultraheavy" dark matter candidates with masses between roughly $10~{\rm TeV}$ and the Planck scale $m_{\rm pl} \approx 10^{16}~{\rm TeV}$. This mass range presents a wide and relatively unexplored dark matter parameter space, with a rich space of possible models and cosmic histories. We emphasize that both current detectors and new, targeted search techniques, via both direct and indirect detection, are poised to contribute to searches for ultraheavy particle dark matter in the coming decade. We highlight the need for new developments in this space, including new analyses of current and imminent direct and indirect experiments targeting ultraheavy dark matter and development of new, ultra-sensitive detector technologies like next-generation liquid noble detectors, neutrino experiments, and specialized quantum sensing techniques