arXiv subjects

N. J. C. Spooner

Publications and source records attributed to N. J. C. Spooner.

At least 109 records · Page 6Linked to original sources

arXiv2006

Measurement of the Scintillation Efficiency of Na Recoils in NaI(Tl) down to 10 keV Nuclear Recoil Energy relevant to Dark Matter Searches

We present preliminary results of measurements of the quenching factor for Na recoils in NaI(Tl) at room temperature, made at a dedicated neutron facility at the University of Sheffield. Measurements have been performed with a 2.45 MeV mono-energetic neutron generator in the energy range from 10 keV to 100 keV nuclear recoil energy. A BC501A liquid scintillator detector was used to tag neutrons. Cuts on pulse-shape discrimination from the BC501A liquid scintillator detector and neutron time-of-flight were performed on pulses recorded by a digitizer with a 2 ns sampling time. Measured quenching factors range from 19% to 26%, in agreement with other experiments. From pulse-shape analysis, a mean time of pulses from electron and nuclear recoils are compared down to 2 keV electron equivalent energy.

physics.ins-det↗

arXiv2006

A two-phase argon avalanche detector operated in a single electron counting mode

The performance of a two-phase Ar avalanche detector in a single electron counting mode was studied, with regard to potential application in coherent neutrino-nucleus scattering and dark matter search experiments. The detector comprised of a 1 cm thick liquid Ar layer and a triple-GEM multiplier operated in the saturated vapour above the liquid phase. Successful operation of the detector in single electron counting mode, in the gain range from 6000 to 40000, has for the first time been demonstrated.

physics.ins-det↗

arXiv2006

The ZEPLIN-III dark matter detector: instrument design, manufacture and commissioning

We present details of the technical design and manufacture of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase xenon detector which measures both the scintillation light and the ionisation charge generated in the liquid by interacting particles and radiation. The instrument design is driven by both the physics requirements and by the technology requirements surrounding the use of liquid xenon. These include considerations of key performance parameters, such as the efficiency of scintillation light collection, restrictions placed on the use of materials to control the inherent radioactivity levels, attainment of high vacuum levels and chemical contamination control. The successful solution has involved a number of novel design and manufacturing features which will be of specific use to future generations of direct dark matter search experiments as they struggle with similar and progressively more demanding requirements.

astro-ph↗

arXiv2006

The ZEPLIN-III dark matter detector: performance study using an end-to-end simulation tool

We present results from a GEANT4-based Monte Carlo tool for end-to-end simulations of the ZEPLIN-III dark matter experiment. ZEPLIN-III is a two-phase detector which measures both the scintillation light and the ionisation charge generated in liquid xenon by interacting particles and radiation. The software models the instrument response to radioactive backgrounds and calibration sources, including the generation, ray-tracing and detection of the primary and secondary scintillations in liquid and gaseous xenon, and subsequent processing by data acquisition electronics. A flexible user interface allows easy modification of detector parameters at run time. Realistic datasets can be produced to help with data analysis, an example of which is the position reconstruction algorithm developed from simulated data. We present a range of simulation results confirming the original design sensitivity of a few times $10^{-8}$ pb to the WIMP-nucleon cross-section.

astro-ph↗

arXiv2006

Low energy neutron propagation in MCNPX and GEANT4

Simulations of neutron background from rock for underground experiments are presented. Neutron propagation through two types of rock, lead and hydrocarbon material is discussed. The results show a reasonably good agreement between GEANT4, MCNPX and GEANT3 in transporting low-energy neutrons.

hep-ex↗

arXiv2005

Reduction of Coincident Photomultiplier Noise Relevant to Astroparticle Physics Experiment

In low background and low threshold particle astrophysics experiments using observation of Cherenkov or scintillation light it is common to use pairs or arrays of photomultipliers operated in coincidence. In such circumstances, for instance in dark matter and neutrino experiments, unexpected PMT noise events have been observed, probably arising from generation of light from one PMT being detected by one or more other PMTs. We describe here experimental investigation of such coincident noise events and development of new techniques to remove them using novel pulse shape discrimination procedures. When applied to data from a low background NaI detector with facing PMTs the new procedures are found to improve noise rejection by a factor of 20 over conventional techniques, with significantly reduced loss of signal events.

physics.ins-det↗

arXiv2005

Muon-induced neutron production and detection with GEANT4 and FLUKA

We report on a comparison study of the Monte Carlo packages GEANT4 and FLUKA for simulating neutron production by muons penetrating deep underground. GEANT4 is found to generate fewer neutrons at muon energies above ~100 GeV, by at most a factor of 2 in some materials, which we attribute mainly to lower neutron production in hadronic cascades. As a practical case study, the muon-induced neutron background expected in a 250 kg liquid-xenon WIMP dark matter detector was calculated and good agreement was found for the recoil event rates. The detailed model of neutron elastic scattering in GEANT4 was also shown to influence the nuclear recoil spectrum observed in the target, which is presently a shortcoming of FLUKA. We conclude that both packages are suited for this type of simulation, although further improvements are desirable in both cases.

hep-ex↗

arXiv2004

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 (alpha,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.

hep-ex↗

arXiv2003

Measurements of muon flux at 1070 metres vertical depth in the Boulby underground laboratory

Measurements of cosmic-ray muon rates and energy deposition spectra in a one tonne liquid scintillator detector at 1070 metres vertical depth in the Boulby underground laboratory are discussed. In addition, the simulations used to model the detector are described. The results of the simulations are compared to the experimental data and conclusions given. The muon flux in the laboratory is found to be (4.09+/-0.15)x10^-8 /cm^2/s.

hep-ex↗

arXiv2003

Simulations of muon-induced neutron flux at large depths underground

The production of neutrons by cosmic-ray muons at large depths underground is discussed. The most recent versions of the muon propagation code MUSIC, and particle transport code FLUKA are used to evaluate muon and neutron fluxes. The results of simulations are compared with experimental data.

hep-ex↗

arXiv2003

The NAIAD experiment for WIMP searches at Boulby mine and recent results

The NAIAD experiment (NaI Advanced Detector) for WIMP dark matter searches at Boulby mine (UK) is described. The detector consists of an array of encapsulated and unencapsulated NaI(Tl) crystals with high light yield. Six crystals are collecting data at present. Data accumulated by four of them (10.6 kg x year exposure) have been used to set upper limits on the WIMP-nucleon spin-independent and WIMP-proton spin-dependent cross-sections. Pulse shape analysis has been applied to discriminate between nuclear recoils, as may be caused by WIMP interactions, and electron recoils due to gamma background. Various calibrations of crystals are presented.

hep-ex↗

arXiv2003

Neutron background at Boulby mine

The neutron background at the underground laboratory at Boulby - a site for several dark matter experiments - is discussed. Special emphasis is put on the neutron background produced by cosmic-ray muons. The most recent versions of the muon propagation code MUSIC, and particle transport code FLUKA are used to evaluate muon and neutron fluxes. The results of simulations are compared with experimental data.

hep-ex↗

arXiv2001

Limits on WIMP Dark Matter

The current state searches for dark matter in the form of Weakly Interacting Massive Particles (WIMPs) using both direct and indirect techniques is reviewed. Advances in recent years by various direct search experiments, utilising technology able to record the nuclear recoil events expected from elastic scattering by WIMPs, have allowed progress towards lower limits to be made. In particular, the Edelweiss and CDMS collaborations are achieving sensitiviy able to challenge data from DAMA interpreted as evidence for WIMPs of mass in the region of 60 GeV. Meanwhile, indirect searches, based on observing the annihilation products of neutralino-neutralino interactions in the Earth, Sun and Galaxy, have produced intriguing results. For instance, analysis by Superkamiokande now suggests limits comparable with the best direct search results.

astro-ph↗

arXiv2001

Study and suppression of anomalous fast events in inorganic scintillators for dark matter searches

The status of dark matter searches with inorganic scintillator detectors at Boulby mine is reviewed and the results of tests with a CsI(Tl) crystal are presented. The objectives of the latter experiment were to study anomalous fast events previously observed and to identify ways to remove this background. Clear indications were found that these events were due to surface contamination of crystals by alphas, probably from radon decay. A new array of unencapsulated NaI(Tl) crystals immersed either in liquid paraffin or pure nitrogen atmosphere is under construction at Boulby. Such an approach allows complete control of the surface of the crystals and the ability to remove any surface contamination. First data from the unencapsulated NaI(Tl) do not show the presence of anomalous fast events.

hep-ex↗

arXiv2001

Measurements of Scintillation Efficiency and Pulse-Shape for Low Energy Recoils in Liquid Xenon

Results of observations of low energy nuclear and electron recoil events in liquid xenon scintillator detectors are given. The relative scintillation efficiency for nuclear recoils is 0.22 +/- 0.01 in the recoil energy range 40 keV - 70 keV. Under the assumption of a single dominant decay component to the scintillation pulse-shape the log-normal mean parameter T0 of the maximum likelihood estimator of the decay time constant for 6 keV < Eee < 30 keV nuclear recoil events is equal to 21.0 ns +/- 0.5 ns. It is observed that for electron recoils T0 rises slowly with energy, having a value ~ 30 ns at Eee ~ 15 keV. Electron and nuclear recoil pulse-shapes are found to be well fitted by single exponential functions although some evidence is found for a double exponential form for the nuclear recoil pulse-shape.

hep-ex↗

arXiv2000

Energy calibration of large underwater detectors using stopping muons

We propose to use stopping cosmic-ray muons in the energy calibration of planned and deployed large underwater detectors. The method is based on the proportionality between the incident muon energy and the length of the muon path before it stops. Simultaneous measurements of the muon path and the amplitude of the signal from the photomultiplier tubes allow a relation between the energy deposited in the sensitive volume of the detector and the observed signal to be derived, and also provide a test of detector simulations. We describe the proposed method and present the results of simulations.

hep-ex↗

arXiv2000

CsI(Tl) for WIMP dark matter searches

We report a study of CsI(Tl) scintillator to assess its applicability in experiments to search for dark matter particles. Measurements of the mean scintillation pulse shapes due to nuclear and electron recoils have been performed. We find that, as with NaI(Tl), pulse shape analysis can be used to discriminate between electron and nuclear recoils down to 4 keV. However, the discrimination factor is typically (10-15)% better than in NaI(Tl) above 4 keV. The quenching factor for caesium and iodine recoils was measured and found to increase from 11% to ~17% with decreasing recoil energy from 60 to 12 keV. Based on these results, the potential sensitivity of CsI(Tl) to dark matter particles in the form of neutralinos was calculated. We find an improvement over NaI(Tl) for the spin independent WIMP-nucleon interactions up to a factor of 5 assuming comparable electron background levels in the two scintillators.

hep-ex↗

arXiv1999

Narrow muon bundles from muon pair production in rock

We revise the process of muon pair production by high-energy muons in rock using the recently published cross-section. The three-dimensional Monte Carlo code MUSIC has been used to obtain the characteristics of the muon bundles initiated via this process. We have compared them with those of conventional muon bundles initiated in the atmosphere and shown that large underground detectors, capable of collecting hundreds of thousands of multiple muon events, can discriminate statistically muon induced bundles from conventional ones. However, we find that the enhancement of the measured muon decoherence function over that predicted at small distances, recently reported by the MACRO experiment, cannot be explained by the effect of muon pair production alone, unless its cross-section is underestimated by a factor of 3.

hep-ph↗