Xenon Dark Matter Detectors Research Articles

Using a Wavelength Shifter to Enhance the Sensitivity of Liquid Xenon Dark Matter Detectors

Liquid xenon dark matter detectors have been successfully employed to search for WIMPs, a proposed dark matter candidate. Increasing the scintillation wavelength from 175 nm to 300-400 nm can increase light collection and consequently improve sensitivity to dark matter. Such a shift increases the reflectivity of common reflector materials, decreases the amount of Rayleigh scattering and boosts the quantum efficiency of photomultiplier tubes. In this paper, we show that depositing p-terphenyl (p-TP) solid wavelength shifter on PTFE reflectors and the entrance window of a photomultiplier tube enhanced light-collection efficiency by 21%. We also observed an anti-correlation between the liquid xenon temperature and electron drift length, indicating that the p-TP dissolves into liquid xenon with a temperature dependent solubility. Possible ways to solve the drift length problem are discussed in the paper.

The ZEPLIN II dark matter detector: Data acquisition system and data reduction

ZEPLIN II is a two-phase (liquid/gas) xenon dark matter detector searching for WIMP-nucleon interactions. In this paper we describe the data acquisition system used to record the data from ZEPLIN II and the reduction procedures which parameterise the data for subsequent analysis.

Performance and Fundamental Processes at Low Energy in a Two-Phase Liquid Xenon Dark Matter Detector

We extend the study of the performance of a prototype two-phase liquid xenon WIMP dark matter detector to recoil energies below 20 keV. We demonstrate a new method for obtaining the best estimate of the energies of events using a calibrated sum of charge and light signals and introduce the corresponding discrimination parameter, giving its mean value at 4 kV/cm for electron and nuclear recoils up to 300 and 100 keV, respectively. We show that fluctuations in recombination limit discrimination for most energies, and reveal an improvement in discrimination below 20 keV due to a surprising increase in ionization yield for low energy electron recoils. This improvement is crucial for a high-sensitivity dark matter search.

Performance and fundamental processes at low energy in a two-phase liquid xenon dark matter detector

We extend the study of the performance of a prototype two-phase liquid xenon WIMP dark matter detector to recoil energies below 20 keV. We demonstrate a new method for obtaining the best estimate of the energies of events using a calibrated sum of charge and light signals and introduce the corresponding discrimination parameter, giving its mean value at 4 kV/cm for electron and nuclear recoils up to 100 keV (nuclear recoil energy). We show that fluctuations in recombination limit discrimination for most energies, and reveal an improvement in discrimination below 20 keV due to a surprising increase in ionization yield for low energy electron recoils. This improvement is crucial for a high-sensitivity dark matter search.

Veto performance for large-scale xenon dark matter detectors

Monte Carlo simulations of the veto performance for large-scale liquid xenon dark matter detectors are presented. A number of possible veto configurations are considered with the aim of maximising the neutron and gamma rejection efficiency. Also discussed are the shielding requirements for reducing the external gamma background.

Simulation of neutron background for future large-scale particle dark matter detectors

Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10 −9–10 −10 pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector.

Neutron background in large-scale xenon detectors for dark matter searches

Simulations of the neutron background for future large-scale particle dark matter detectors are presented. Neutrons were generated in rock and detector elements via spontaneous fission and (α,n) reactions, and by cosmic-ray muons. The simulation techniques and results are discussed in the context of the expected sensitivity of a generic liquid xenon dark matter detector. Methods of neutron background suppression are investigated. A sensitivity of 10−9–10−10 pb to WIMP-nucleon interactions can be achieved by a tonne-scale detector.

Simulation and analysis for astroparticle experiments

The simulation of Astroparticle experiments using the Geant4 toolkit is presented with emphasis on the low energy electromagnetic extension and object orientated analysis via AIDA and the ANAPHE package. Comparison is made between simulation and experimental data from a prototype xenon dark matter detector. Pulse shape discrimination between α's and γ's has been demonstrated on the basis of different scintillation time constants of 24 ns and 42 ns, respectively. The LISA gravitational wave spacecraft has been modelled and background charging due to cosmic particle fluxes estimated to be 58 positive charges per second for a 45 second exposure (10 million events). The simulation was run in a distributed environment of 130 processor nodes. Other applications of Geant4 and AIDA to space and underground Astroparticle experiments are identified.

Development of a two-phase xenon dark matter detector

The current status of the development study focused on building a novel two-phase xenon detector for dark matter search is described. Discrimination of the radioactive background is based on particle identification that comes from the analysis of the scintillation-to-ionization ratio. Electroluminescence (proportional scintillation) is used for “amplification” of the ionization signal.

Monte Carlo studies of ZEPLIN III

A Monte Carlo simulation of a two-phase xenon dark matter detector, ZEPLIN III, has been achieved. Results from the analysis of a simulated data set are presented, showing primary and secondary signal distributions from low energy gamma ray events.