Author: Marc WeberPublisher:
ISBN:
Category :
Languages : en
Pages : 135
Book Description
Gentle Neutron Signals and Noble Background in the XENON100 Dark Matter Search Experiment
Author: Marc WeberStudy on Neutron-induced Background in the Dark Matter Experiment CRESST
Author: Hesti R. T. WulandariPublisher:
ISBN: 9783897913196
Category :
Languages : en
Pages : 246
Book Description
Commissioning of the World's First Water Cherenkov Neutron Veto and First WIMP Dark Matter Search Results of the XENONnT Experiment
Author: Daniel WenzPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
A rich number of astronomical and cosmological observations suggest the existence of a massive, non-luminous, and non-relativistic, matter component in the universe which is five times more abundant than baryonic matter and is commonly referred as to dark matter (DM). Although so far eluding from detection, one class of promising DM candidates are weakly interacting massive particles (WIMPs) which arise naturally from many beyond the Standard Model (BSM) theories. The XENON Dark Matter Project aims to directly detect WIMPs, and other kinds of rare event signals, by utilizing large-scale liquid xenon (LXe) dual-phase time projection chambers (TPCs). The newest generation of experiment, called XENONnT, utilizes a TPC with a total sensitive LXe mass of 5.9 t, and was designed as a fast upgrade of its predecessor XENON1T. In addition to its larger TPC, XENONnT was augmented with the world's first water Cherenkov neutron veto (NV), which was mounted inside the already existing water Cherenkov muon veto water tank of XENON1T. Neutrons emitted by detector materials can undergo a single back-scatter inside the TPC producing a signal which is indistinguishable from WIMPs. The NV has the task to mitigate this potential threat for the scientific reach of the experiment by tagging these escaping neutrons through their delayed neutron capture on hydrogen. In the presented work, the results of the first weakly interacting massive particle (WIMP) search science run, called SR0, are discussed. SR0 features a blind analysis between 3.3 keV and 60.5 keV nuclear recoils energies with a total exposure of about 1.1 tonne-year, utilizing the lowest ever achieved electronic recoil background of (15.8 ± 1.3) events/(t · y · keV) in a LXe. No significant excess was found in the data, setting the lowest upper limit of 2.58 · 10-47 cm2 for spin-independent (SI) interactions of 28 GeV/c2 WIMPs at a 90% confidence level. These results have also been published in [Apr+23b] as part of the presented work. To obtain these results, this thesis discusses the commissioning of the XENONnT neutron veto (NV), and the calibration of its neutron tagging efficiency. The tagging efficiency was found to be (53.1±2.8)% which is the highest efficiency ever measured in a water Cherenkov detector. The efficiency of the NV, as well as the nuclear recoil (NR) response of the time projection chamber (TPC), were calibrated using tagged neutrons from an Americium-Beryllium (AmBe) neutron source. This technique was deployed for the first time in a liquid xenon (LXe) TPC. It enables a calibration of the NR response with high purity and a remaining pollution of less than 0.1 %. Further, the same calibration data was used to determine the thermal neutron capture cross section of hydrogen which was found to be 336.7 ± 0.4 (stat.)+2.0 -0.0 (sys.) mb. All these analyses are based on the data provided by XENONnT's new processing framework called STRAXEN. As part of the lead developing team, the entire processing chain for the two veto systems of XENONnT was developed, and many additional tools have been implemented. Finally, to enhance the neutron tagging efficiency of the NV even further, the water inside the water tank is going to be doped with Gd-sulfate. As part of the presented work, different Gd-salt samples of the manufacturer Treibacher were analyzed regarding their suitability for the experiment.
A Study of Nuclear Recoil Backgrounds in Dark Matter Detectors
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 394
Book Description
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 from 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 ($\alpha$, 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 e_ciency to allow DarkSide-50 to run background-free for three years.
Dark Matter Search with the XENON100 Experiment
Author: Alexander KishCharacterization of Neutron Backgrounds for Direct Dark Matter Searches
Author: Melinda Dominique SweanyPublisher:
ISBN: 9781267029393
Category :
Languages : en
Pages :
Book Description
Direct dark matter experiments generally cannot distinguish between nuclear recoils caused by Weakly Interacting Massive Particles (WIMPs) and those caused by neutron backgrounds. It is therefore crucial that all sources of neutron background are well understood and accounted for when claiming a discovery or reporting limits on the WIMP-nucleon cross section. One source of neutrons that is not well understood results from cosmogenic muon interactions in the material surrounding a detector. The Neutron Multiplicity Meter in the Soudan cavern is a gadolinium-doped water Cherenkov detector capable of detecting high multiplicity neutron showers resulting from fast neutrons incident on a lead target. This measurement is the first such measurement obtained without a liquid scintillator detector medium; muon and neutron spallation is media-dependent, and because neutron shield technology for dark matter detectors is moving towards water, this is an important measurement. The integrated fast neutron flux in the Soudan cavern is reported as a linear function of the power, [alpha], of the neutron angular distribution with the zenith angle: [Fourier transform] = 4.8x10−9 ± 3.5x10−10 + (5.4x10−10 ± 1.5x10−10)[alpha]. Technological studies of neutron detection with gadolinium-doped water are also reported here. The neutron detection efficiency of a cylindrical 3.5 kL detector is measured at 70% for neutrons in the center of the detector. In addition, other improvements to water Cherenkov technology are explored, namely the addition of water-soluble wavelength-shifting chemicals. The wavelength-shifting chemical 4-Methylumbelliferone has been shown here to increase the measured light output of Cherenkov radiation resulting from neutron capture showers by a factor of 1.7.
Characterizing the Peripheral Dynamics of Xenon Dark Matter Detectors
Author: Jacob Edward CutterPublisher:
ISBN:
Category :
Languages : en
Pages : 0
Book Description
One of the most important fundamental problems in physics today is to understand the nature of dark matter. The landscape of explanations for observed dark matter phenomena is vast and still expanding, and an impressive number of experiments have been built to probe the dark sector of the universe. A prominent class of detectors is aimed at discovering (or excluding) a particular kind of dark matter: the Weakly Interacting Massive Particle (WIMP). Searching for this popular dark matter candidate requires an ultra-sensitive, low-background target; xenon detectors serve as such a target for dark matter interactions. The Large Underground Xenon (LUX) detector is a dual-phase xenon time-projection chamber (TPC) which was operated underground at the Homestake Mine in Lead, South Dakota from 2013 to 2016, and was able to achieve the world's leading WIMP exclusion limit. However, successful reconstruction of WIMP-nucleus scatters in such detectors requires thorough understanding of the detection medium, which is made difficult by various confounding effects near the detector walls. Field-fringing is a major component of confusion in the periphery, and the large electric field non-uniformities in Run 4 of LUX provided a significant challenge in the dark matter analysis. Here is presented an algorithm to bijectively map between reconstructed event positions and true spatial coordinates, which serves as an important tool for studying field effects and fiducialization in LUX. Additionally, a successful dark matter search must model interfering background events in the WIMP search region which can't be directly vetoed. One class of unavoidable backgrounds comes from nuclear decay chain daughters in detector materials themselves, which may produce WIMP-like signals (an effect which is amplified due to various detector effects). The Davis Xenon (DAX) test bed system and a dual-phase TPC have been assembled and operated at UC Davis to characterize these common "wall backgrounds", as well as perform other R&D studies for the next-generation LUX-ZEPLIN (LZ) experiment. The DAX TPC specifically measures the xenon response to heavy nuclei produced by custom [alpha] decay sources created using novel chemical deposition procedures. In this thesis, results will be presented for the light and charge yields of immersed localized sources of 206Pb ions in liquid xenon, as well as a method for tagging such recoil events in situ by using PIN diodes as charged particle detectors to capture the correlated [alpha] particles. We also compare our isolated 206Pb events with previous WIMP search data from LUX, and discuss the significance of 206Pb as a WIMP background. Such information is most useful to future experiments if it can improve existing background models and simulations. The Noble Element Simulation Technique (NEST) is the ultimate software package for calculating expected signal yields in xenon detectors, but is an empirical framework that relies on experimental data to inform the models. We discuss the development of current NEST v2 models, specifically the heavy nuclear recoil models, as well as our current understanding of the xenon microphysics. We also show NEST predictions for mono-energetic 206Pb recoils, and discuss how our most recent DAX 206Pb measurements may inform NEST models in future work.
Search for Low Mass Dark Matter with the XENON100 Experiment and Simulations for 1 Ton and 10 Ton Dark Matter Detectors
Author: Ethan Craig BrownSimulations of the Muon-induced Neutron Background of the EDELWEISS-II Experiment for Dark Matter Search
Author: Oliver Markus HornStudy of Neutrino Background for the Low-mass Dark Matter Search in Future Neutrino Experiments
Author: Aayush BhattaraiPublisher:
ISBN:
Category :
Languages : en
Pages : 30
Book Description
With high-intensity neutrino beams and large mass detectors, neutrino physics has entered the high precision measurement era. Accelerator experiments that use highintensity proton beams impinging on a fixed target could produce dark matter along with neutrinos. DUNE, one of the most extensive neutrino experiments under construction, has similar prospects of looking for low-mass dark matter (LDM) produced in the proton interactions with the target. With the possibility of charge-neutral LDM production in the target, numerous neutrinos will be generated alongside it, which will be the primary background to the LDM signal. To understand these neutrino backgrounds, we studied two “modified DUNE” frameworks: Neutral Rich Horn Focusing (NRHF) System and Targetless DUNE. These systems help us reduce background neutrinos in search of LDM signals. These configurations also enhance the signal-to-background ratio by several orders of magnitude.